| Message ID | 20180912121955.33048-2-cychiang@chromium.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [1/2] ASoC: max9892x: Add documentation for reset-gpio support | expand |
On 9/12/2018 5:49 PM, Cheng-Yi Chiang wrote: > Toggle reset line in max98927_i2c_probe. > Use a list to store max98927 instances so we do not toggle reset line > again if more than one instances share the same reset line. > > Signed-off-by: Cheng-Yi Chiang <cychiang@chromium.org> Reviewed-and-tested-by: Rohit kumar <rohitkr@codeaurora.org> > --- > sound/soc/codecs/max98927.c | 78 +++++++++++++++++++++++++++++++++++++++++++++ > sound/soc/codecs/max98927.h | 2 ++ > 2 files changed, 80 insertions(+) > > diff --git a/sound/soc/codecs/max98927.c b/sound/soc/codecs/max98927.c > index 941712058a8f5..789b27cdfd9e0 100644 > --- a/sound/soc/codecs/max98927.c > +++ b/sound/soc/codecs/max98927.c > @@ -11,6 +11,7 @@ > */ > > #include <linux/acpi.h> > +#include <linux/delay.h> > #include <linux/i2c.h> > #include <linux/module.h> > #include <linux/regmap.h> > @@ -24,6 +25,11 @@ > #include <sound/tlv.h> > #include "max98927.h" > > +#define MAX98927_MIN_RESET_US 1 > +#define MAX98927_RELEASE_RESET_DELAY_US 500 > + > +static LIST_HEAD(reset_list); > + > static struct reg_default max98927_reg[] = { > {MAX98927_R0001_INT_RAW1, 0x00}, > {MAX98927_R0002_INT_RAW2, 0x00}, > @@ -877,6 +883,54 @@ static void max98927_slot_config(struct i2c_client *i2c, > max98927->i_l_slot = 1; > } > > +static int max98927_i2c_toggle_reset(struct device *dev, > + struct max98927_priv *max98927) > +{ > + /* > + * If we do not have reset gpio, assume platform firmware > + * controls the regulator and toggles it for us. > + */ > + if (!max98927->reset_gpio) > + return 0; > + > + gpiod_set_value_cansleep(max98927->reset_gpio, 1); > + > + /* > + * We need to wait a bit before we are allowed to release reset GPIO. > + */ > + usleep_range(MAX98927_MIN_RESET_US, MAX98927_MIN_RESET_US + 5); > + > + gpiod_set_value_cansleep(max98927->reset_gpio, 0); > + > + /* > + * We need to wait a bit before I2C communication is available. > + */ > + usleep_range(MAX98927_RELEASE_RESET_DELAY_US, > + MAX98927_RELEASE_RESET_DELAY_US + 5); > + > + /* > + * Release reset GPIO because we are not going to use it. > + */ > + devm_gpiod_put(dev, max98927->reset_gpio); > + > + return 0; > +} > + > +static bool max98927_is_first_to_reset(struct max98927_priv *max98927) > +{ > + struct max98927_priv *p; > + > + if (!max98927->reset_gpio) > + return false; > + > + list_for_each_entry(p, &reset_list, list) { > + if (max98927->reset_gpio == p->reset_gpio) > + return false; > + } > + > + return true; > +} > + > static int max98927_i2c_probe(struct i2c_client *i2c, > const struct i2c_device_id *id) > { > @@ -904,6 +958,28 @@ static int max98927_i2c_probe(struct i2c_client *i2c, > } else > max98927->interleave_mode = 0; > > + /* Gets optional GPIO for reset line. */ > + max98927->reset_gpio = devm_gpiod_get_optional( > + &i2c->dev, "reset", GPIOD_OUT_LOW); > + if (IS_ERR(max98927->reset_gpio)) { > + ret = PTR_ERR(max98927->reset_gpio); > + dev_err(&i2c->dev, "error getting reset gpio: %d\n", ret); > + return ret; > + } > + > + /* > + * Only toggle reset line for the first instance when the > + * reset line is shared among instances. For example, > + * left and right amplifier share the same reset line, and > + * we should only toggle the reset line once. > + */ > + if (max98927_is_first_to_reset(max98927)) { > + dev_info(&i2c->dev, "%s: toggle reset line\n", __func__); > + ret = max98927_i2c_toggle_reset(&i2c->dev, max98927); > + if (ret) > + return ret; > + } > + > /* regmap initialization */ > max98927->regmap > = devm_regmap_init_i2c(i2c, &max98927_regmap); > @@ -934,6 +1010,8 @@ static int max98927_i2c_probe(struct i2c_client *i2c, > if (ret < 0) > dev_err(&i2c->dev, "Failed to register component: %d\n", ret); > > + list_add(&max98927->list, &reset_list); > + > return ret; > } > > diff --git a/sound/soc/codecs/max98927.h b/sound/soc/codecs/max98927.h > index 538992a238b28..d48f61f6c3ba5 100644 > --- a/sound/soc/codecs/max98927.h > +++ b/sound/soc/codecs/max98927.h > @@ -275,5 +275,7 @@ struct max98927_priv { > unsigned int master; > unsigned int digital_gain; > bool tdm_mode; > + struct gpio_desc *reset_gpio; > + struct list_head list; > }; > #endif
Hi Mark, Do you have any concern about this patch ? Thanks! On Thu, Sep 13, 2018 at 12:47 AM Rohit Kumar <rohitkr@codeaurora.org> wrote: > > > > On 9/12/2018 5:49 PM, Cheng-Yi Chiang wrote: > > Toggle reset line in max98927_i2c_probe. > > Use a list to store max98927 instances so we do not toggle reset line > > again if more than one instances share the same reset line. > > > > Signed-off-by: Cheng-Yi Chiang <cychiang@chromium.org> > Reviewed-and-tested-by: Rohit kumar <rohitkr@codeaurora.org> > > > --- > > sound/soc/codecs/max98927.c | 78 +++++++++++++++++++++++++++++++++++++++++++++ > > sound/soc/codecs/max98927.h | 2 ++ > > 2 files changed, 80 insertions(+) > > > > diff --git a/sound/soc/codecs/max98927.c b/sound/soc/codecs/max98927.c > > index 941712058a8f5..789b27cdfd9e0 100644 > > --- a/sound/soc/codecs/max98927.c > > +++ b/sound/soc/codecs/max98927.c > > @@ -11,6 +11,7 @@ > > */ > > > > #include <linux/acpi.h> > > +#include <linux/delay.h> > > #include <linux/i2c.h> > > #include <linux/module.h> > > #include <linux/regmap.h> > > @@ -24,6 +25,11 @@ > > #include <sound/tlv.h> > > #include "max98927.h" > > > > +#define MAX98927_MIN_RESET_US 1 > > +#define MAX98927_RELEASE_RESET_DELAY_US 500 > > + > > +static LIST_HEAD(reset_list); > > + > > static struct reg_default max98927_reg[] = { > > {MAX98927_R0001_INT_RAW1, 0x00}, > > {MAX98927_R0002_INT_RAW2, 0x00}, > > @@ -877,6 +883,54 @@ static void max98927_slot_config(struct i2c_client *i2c, > > max98927->i_l_slot = 1; > > } > > > > +static int max98927_i2c_toggle_reset(struct device *dev, > > + struct max98927_priv *max98927) > > +{ > > + /* > > + * If we do not have reset gpio, assume platform firmware > > + * controls the regulator and toggles it for us. > > + */ > > + if (!max98927->reset_gpio) > > + return 0; > > + > > + gpiod_set_value_cansleep(max98927->reset_gpio, 1); > > + > > + /* > > + * We need to wait a bit before we are allowed to release reset GPIO. > > + */ > > + usleep_range(MAX98927_MIN_RESET_US, MAX98927_MIN_RESET_US + 5); > > + > > + gpiod_set_value_cansleep(max98927->reset_gpio, 0); > > + > > + /* > > + * We need to wait a bit before I2C communication is available. > > + */ > > + usleep_range(MAX98927_RELEASE_RESET_DELAY_US, > > + MAX98927_RELEASE_RESET_DELAY_US + 5); > > + > > + /* > > + * Release reset GPIO because we are not going to use it. > > + */ > > + devm_gpiod_put(dev, max98927->reset_gpio); > > + > > + return 0; > > +} > > + > > +static bool max98927_is_first_to_reset(struct max98927_priv *max98927) > > +{ > > + struct max98927_priv *p; > > + > > + if (!max98927->reset_gpio) > > + return false; > > + > > + list_for_each_entry(p, &reset_list, list) { > > + if (max98927->reset_gpio == p->reset_gpio) > > + return false; > > + } > > + > > + return true; > > +} > > + > > static int max98927_i2c_probe(struct i2c_client *i2c, > > const struct i2c_device_id *id) > > { > > @@ -904,6 +958,28 @@ static int max98927_i2c_probe(struct i2c_client *i2c, > > } else > > max98927->interleave_mode = 0; > > > > + /* Gets optional GPIO for reset line. */ > > + max98927->reset_gpio = devm_gpiod_get_optional( > > + &i2c->dev, "reset", GPIOD_OUT_LOW); > > + if (IS_ERR(max98927->reset_gpio)) { > > + ret = PTR_ERR(max98927->reset_gpio); > > + dev_err(&i2c->dev, "error getting reset gpio: %d\n", ret); > > + return ret; > > + } > > + > > + /* > > + * Only toggle reset line for the first instance when the > > + * reset line is shared among instances. For example, > > + * left and right amplifier share the same reset line, and > > + * we should only toggle the reset line once. > > + */ > > + if (max98927_is_first_to_reset(max98927)) { > > + dev_info(&i2c->dev, "%s: toggle reset line\n", __func__); > > + ret = max98927_i2c_toggle_reset(&i2c->dev, max98927); > > + if (ret) > > + return ret; > > + } > > + > > /* regmap initialization */ > > max98927->regmap > > = devm_regmap_init_i2c(i2c, &max98927_regmap); > > @@ -934,6 +1010,8 @@ static int max98927_i2c_probe(struct i2c_client *i2c, > > if (ret < 0) > > dev_err(&i2c->dev, "Failed to register component: %d\n", ret); > > > > + list_add(&max98927->list, &reset_list); > > + > > return ret; > > } > > > > diff --git a/sound/soc/codecs/max98927.h b/sound/soc/codecs/max98927.h > > index 538992a238b28..d48f61f6c3ba5 100644 > > --- a/sound/soc/codecs/max98927.h > > +++ b/sound/soc/codecs/max98927.h > > @@ -275,5 +275,7 @@ struct max98927_priv { > > unsigned int master; > > unsigned int digital_gain; > > bool tdm_mode; > > + struct gpio_desc *reset_gpio; > > + struct list_head list; > > }; > > #endif >
On Mon, Sep 17, 2018 at 05:00:28PM +0800, Cheng-yi Chiang wrote: > Hi Mark, > Do you have any concern about this patch ? Please don't send content free pings and please allow a reasonable time for review. People get busy, go on holiday, attend conferences and so on so unless there is some reason for urgency (like critical bug fixes) please allow at least a couple of weeks for review. If there have been review comments then people may be waiting for those to be addressed. Sending content free pings just adds to the mail volume (if they are seen at all) and if something has gone wrong you'll have to resend the patches anyway.
Hi Cheng-Yi,
Thank you for the patch! Yet something to improve:
[auto build test ERROR on asoc/for-next]
[also build test ERROR on v4.19-rc4 next-20180919]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]
url: https://github.com/0day-ci/linux/commits/Cheng-Yi-Chiang/ASoC-max9892x-Add-documentation-for-reset-gpio-support/20180914-010006
base: https://git.kernel.org/pub/scm/linux/kernel/git/broonie/sound.git for-next
config: x86_64-randconfig-s3-09201857 (attached as .config)
compiler: gcc-7 (Debian 7.3.0-1) 7.3.0
reproduce:
# save the attached .config to linux build tree
make ARCH=x86_64
All errors (new ones prefixed by >>):
sound/soc/codecs/max98927.c: In function 'max98927_i2c_toggle_reset':
>> sound/soc/codecs/max98927.c:884:2: error: implicit declaration of function 'gpiod_set_value_cansleep'; did you mean 'gpio_set_value_cansleep'? [-Werror=implicit-function-declaration]
gpiod_set_value_cansleep(max98927->reset_gpio, 1);
^~~~~~~~~~~~~~~~~~~~~~~~
gpio_set_value_cansleep
>> sound/soc/codecs/max98927.c:902:2: error: implicit declaration of function 'devm_gpiod_put'; did you mean 'devm_gpio_free'? [-Werror=implicit-function-declaration]
devm_gpiod_put(dev, max98927->reset_gpio);
^~~~~~~~~~~~~~
devm_gpio_free
sound/soc/codecs/max98927.c: In function 'max98927_i2c_probe':
>> sound/soc/codecs/max98927.c:950:25: error: implicit declaration of function 'devm_gpiod_get_optional'; did you mean 'devm_gpio_request_one'? [-Werror=implicit-function-declaration]
max98927->reset_gpio = devm_gpiod_get_optional(
^~~~~~~~~~~~~~~~~~~~~~~
devm_gpio_request_one
>> sound/soc/codecs/max98927.c:951:24: error: 'GPIOD_OUT_LOW' undeclared (first use in this function); did you mean 'GPIOF_INIT_LOW'?
&i2c->dev, "reset", GPIOD_OUT_LOW);
^~~~~~~~~~~~~
GPIOF_INIT_LOW
sound/soc/codecs/max98927.c:951:24: note: each undeclared identifier is reported only once for each function it appears in
cc1: some warnings being treated as errors
vim +884 sound/soc/codecs/max98927.c
873
874 static int max98927_i2c_toggle_reset(struct device *dev,
875 struct max98927_priv *max98927)
876 {
877 /*
878 * If we do not have reset gpio, assume platform firmware
879 * controls the regulator and toggles it for us.
880 */
881 if (!max98927->reset_gpio)
882 return 0;
883
> 884 gpiod_set_value_cansleep(max98927->reset_gpio, 1);
885
886 /*
887 * We need to wait a bit before we are allowed to release reset GPIO.
888 */
889 usleep_range(MAX98927_MIN_RESET_US, MAX98927_MIN_RESET_US + 5);
890
891 gpiod_set_value_cansleep(max98927->reset_gpio, 0);
892
893 /*
894 * We need to wait a bit before I2C communication is available.
895 */
896 usleep_range(MAX98927_RELEASE_RESET_DELAY_US,
897 MAX98927_RELEASE_RESET_DELAY_US + 5);
898
899 /*
900 * Release reset GPIO because we are not going to use it.
901 */
> 902 devm_gpiod_put(dev, max98927->reset_gpio);
903
904 return 0;
905 }
906
907 static bool max98927_is_first_to_reset(struct max98927_priv *max98927)
908 {
909 struct max98927_priv *p;
910
911 if (!max98927->reset_gpio)
912 return false;
913
914 list_for_each_entry(p, &reset_list, list) {
915 if (max98927->reset_gpio == p->reset_gpio)
916 return false;
917 }
918
919 return true;
920 }
921
922 static int max98927_i2c_probe(struct i2c_client *i2c,
923 const struct i2c_device_id *id)
924 {
925
926 int ret = 0, value;
927 int reg = 0;
928 struct max98927_priv *max98927 = NULL;
929
930 max98927 = devm_kzalloc(&i2c->dev,
931 sizeof(*max98927), GFP_KERNEL);
932
933 if (!max98927) {
934 ret = -ENOMEM;
935 return ret;
936 }
937 i2c_set_clientdata(i2c, max98927);
938
939 /* update interleave mode info */
940 if (!of_property_read_u32(i2c->dev.of_node,
941 "interleave_mode", &value)) {
942 if (value > 0)
943 max98927->interleave_mode = 1;
944 else
945 max98927->interleave_mode = 0;
946 } else
947 max98927->interleave_mode = 0;
948
949 /* Gets optional GPIO for reset line. */
> 950 max98927->reset_gpio = devm_gpiod_get_optional(
> 951 &i2c->dev, "reset", GPIOD_OUT_LOW);
952 if (IS_ERR(max98927->reset_gpio)) {
953 ret = PTR_ERR(max98927->reset_gpio);
954 dev_err(&i2c->dev, "error getting reset gpio: %d\n", ret);
955 return ret;
956 }
957
958 /*
959 * Only toggle reset line for the first instance when the
960 * reset line is shared among instances. For example,
961 * left and right amplifier share the same reset line, and
962 * we should only toggle the reset line once.
963 */
964 if (max98927_is_first_to_reset(max98927)) {
965 dev_info(&i2c->dev, "%s: toggle reset line\n", __func__);
966 ret = max98927_i2c_toggle_reset(&i2c->dev, max98927);
967 if (ret)
968 return ret;
969 }
970
971 /* regmap initialization */
972 max98927->regmap
973 = devm_regmap_init_i2c(i2c, &max98927_regmap);
974 if (IS_ERR(max98927->regmap)) {
975 ret = PTR_ERR(max98927->regmap);
976 dev_err(&i2c->dev,
977 "Failed to allocate regmap: %d\n", ret);
978 return ret;
979 }
980
981 /* Check Revision ID */
982 ret = regmap_read(max98927->regmap,
983 MAX98927_R01FF_REV_ID, ®);
984 if (ret < 0) {
985 dev_err(&i2c->dev,
986 "Failed to read: 0x%02X\n", MAX98927_R01FF_REV_ID);
987 return ret;
988 }
989 dev_info(&i2c->dev, "MAX98927 revisionID: 0x%02X\n", reg);
990
991 /* voltage/current slot configuration */
992 max98927_slot_config(i2c, max98927);
993
994 /* codec registeration */
995 ret = devm_snd_soc_register_component(&i2c->dev,
996 &soc_component_dev_max98927,
997 max98927_dai, ARRAY_SIZE(max98927_dai));
998 if (ret < 0)
999 dev_err(&i2c->dev, "Failed to register component: %d\n", ret);
1000
1001 list_add(&max98927->list, &reset_list);
1002
1003 return ret;
1004 }
1005
---
0-DAY kernel test infrastructure Open Source Technology Center
https://lists.01.org/pipermail/kbuild-all Intel Corporation
On Wed, Sep 12, 2018 at 08:19:55PM +0800, Cheng-Yi Chiang wrote: > + /* > + * Release reset GPIO because we are not going to use it. > + */ > + devm_gpiod_put(dev, max98927->reset_gpio); There is no need to do this, it's still potentially useful information for userspace and it's also going to surprise anyone who tries to modify the code to use this function at some other time (eg, when coming out of suspend sometimes it's useful to reset the device). > @@ -934,6 +1010,8 @@ static int max98927_i2c_probe(struct i2c_client *i2c, > if (ret < 0) > dev_err(&i2c->dev, "Failed to register component: %d\n", ret); > > + list_add(&max98927->list, &reset_list); > + I'm not seeing any locking of this list. This also feels like something that shouldn't be in this driver but should be pushed up a level - it's only going to do the right thing if the reset line is only shared with other devices using this driver, if someone does something like put the CODEC and an external speaker amp on the same reset pin then it won't work. I'm not sure where the best place to do that is; drivers/reset isn't really for this use case but feels right perhaps? Can you perhaps split the basic reset handling out from this list handling as a separate patch?
+reset controller maintainer Philipp
Hi Mark,
Sorry for the late reply. It took me a while to investigate reset
controller and its possible usage. I would like to figure out the
proper way of reset handling because it is common to have a shared
reset line for two max98927 codecs for left and right channels.
Without supporting this usage, a simple reset-gpios change for single
codec would not be useful, and perhaps will be duplicated if reset
controller is a better way.
Hi Philipp,
I would like to seek your advice about whether we can use reset
controller to support the use case where multiple devices share the
same reset line.
Let me summarize the use case:
There are two max98927 codecs sharing the same reset line.
The reset line is controlled by a GPIO.
The goal is to toggle reset line once and only once.
There was a similar scenario in tlv320aic3x codec driver [1].
A static list is used in the codec driver so probe function can know
whether it is needed to toggle reset line.
Mark pointed out that it is not suitable to handle the shared reset
line inside codec driver.
A point is that this only works for multiple devices using the same
device driver.
He suggested to look into reset controller so I searched through the
usage for common reset line.
Here I found a shared reset line use case [2].
With the patch [2], reset_control_reset can support this “reset once
and for all” use case.
However, I found that there are some missing pieces:
Let’s assume there are two codecs c1 and c2 sharing a reset line
controlled by GPIO.
c1’s spec:
Hold time: The minimum time to assert the reset line is t_a1.
Release time: The minimum time to access the chip after deassert of
the reset line is t_d1.
c2’s spec:
Hold time: The minimum time to assert the reset line is t_a2.
Release time: The minimum time to access the chip after deassert of
the reset line is t_d2.
For both c1 and c2 to work properly, we need a reset controller that
can assert the reset line for
T = max(t_a1, t_a2).
1. We need reset controller to support GPIO.
2. We need to specify hold time T to reset controller in device tree
so it knows that it needs hold reset line for that long in its
implementation of reset_control_reset.
3. Assuming we have 1 and 2 in place. In codec driver of c1, it can
call reset_control_reset and wait for t_a1 + t_d1. In codec driver of
c2, it can call reset_control_reset and wait for t_a2 + t_d2.
We need to wait for hold time + release time because
triggered_count is increased before reset ops is called. When the
second driver finds that triggered_count is 1 and skip the real reset
operation, reset ops might just begin doing its work a short time ago.
I am not sure whether we would need a flag in reset controller to
mark that "reset is done". When driver sees this flag is done, it can
just wait for release time instead of hold time + release time.
And I found that you already solved 1 and mentioned the
possible usage of 2 in [3].
There were discussion about letting device driver to deal with
reset-gpios by itself in [4], but it seems that reset controller can
better deal with the shared reset line situation.
Maybe we could revive the patch of GPIO support for reset controller ?
Please let me know what direction I should look into.
Thanks a lot!
[1] http://mailman.alsa-project.org/pipermail/alsa-devel/2010-November/033246.html
https://patchwork.kernel.org/patch/9424123/
[2] https://patchwork.kernel.org/patch/9424123/
[3] https://lore.kernel.org/patchwork/patch/455839/
[4] https://patchwork.kernel.org/patch/3978121/
On Fri, Sep 21, 2018 at 12:19 AM Mark Brown <broonie@kernel.org> wrote:
>
> On Wed, Sep 12, 2018 at 08:19:55PM +0800, Cheng-Yi Chiang wrote:
>
> > + /*
> > + * Release reset GPIO because we are not going to use it.
> > + */
> > + devm_gpiod_put(dev, max98927->reset_gpio);
>
> There is no need to do this, it's still potentially useful information
> for userspace and it's also going to surprise anyone who tries to modify
> the code to use this function at some other time (eg, when coming out of
> suspend sometimes it's useful to reset the device).
>
> > @@ -934,6 +1010,8 @@ static int max98927_i2c_probe(struct i2c_client *i2c,
> > if (ret < 0)
> > dev_err(&i2c->dev, "Failed to register component: %d\n", ret);
> >
> > + list_add(&max98927->list, &reset_list);
> > +
>
> I'm not seeing any locking of this list. This also feels like something
> that shouldn't be in this driver but should be pushed up a level - it's
> only going to do the right thing if the reset line is only shared with
> other devices using this driver, if someone does something like put the
> CODEC and an external speaker amp on the same reset pin then it won't
> work. I'm not sure where the best place to do that is; drivers/reset
> isn't really for this use case but feels right perhaps?
>
> Can you perhaps split the basic reset handling out from this list
> handling as a separate patch?
Hi Cheng-yi, [adding Maxime, devicetree to Cc:, the old discussion about GPIO resets in [4] has never been resolved] On Tue, 2018-10-09 at 21:46 +0800, Cheng-yi Chiang wrote: > +reset controller maintainer Philipp > > Hi Mark, > Sorry for the late reply. It took me a while to investigate reset > controller and its possible usage. I would like to figure out the > proper way of reset handling because it is common to have a shared > reset line for two max98927 codecs for left and right channels. > Without supporting this usage, a simple reset-gpios change for single > codec would not be useful, and perhaps will be duplicated if reset > controller is a better way. > > Hi Philipp, > I would like to seek your advice about whether we can use reset > controller to support the use case where multiple devices share the > same reset line. > > Let me summarize the use case: > There are two max98927 codecs sharing the same reset line. > The reset line is controlled by a GPIO. > The goal is to toggle reset line once and only once. > > There was a similar scenario in tlv320aic3x codec driver [1]. > A static list is used in the codec driver so probe function can know > whether it is needed to toggle reset line. > Mark pointed out that it is not suitable to handle the shared reset > line inside codec driver. > A point is that this only works for multiple devices using the same > device driver. > He suggested to look into reset controller so I searched through the > usage for common reset line. > > Here I found a shared reset line use case [2]. > With the patch [2], reset_control_reset can support this “reset once > and for all” use case. This patch was applied as 7da33a37b48f. So the reset framework has support for shared reset controls where only the first reset request actually causes a reset pulse, and all others are no-ops. > However, I found that there are some missing pieces: > > Let’s assume there are two codecs c1 and c2 sharing a reset line > controlled by GPIO. > > c1’s spec: > Hold time: The minimum time to assert the reset line is t_a1. > Release time: The minimum time to access the chip after deassert of > the reset line is t_d1. > > c2’s spec: > Hold time: The minimum time to assert the reset line is t_a2. > Release time: The minimum time to access the chip after deassert of > the reset line is t_d2. > > For both c1 and c2 to work properly, we need a reset controller that > can assert the reset line for > T = max(t_a1, t_a2). > > 1. We need reset controller to support GPIO. I still don't like the idea of describing a separate gpio reset controller "device" in DT very much, as this is really just a software abstraction, not actual hardware. For example: gpio_reset: reset-controller { compatible = "gpio-reset"; reset-gpios = <&gpio0 15 GPIO_ACTIVE_LOW>, <&gpio1 16 GPIO_ACTIVE_HIGH>; reset-delays-us = <10000>, <500>; }; c1 { resets = <&gpio_reset 0>; /* maps to <&gpio0 15 ...> */ }; c2 { resets = <&gpio_reset 0>; }; What I would like better would be to let the consumers keep their reset- gpios bindings, but add an optional hold time override in the DT: c1 { reset-gpios = <&gpio0 15 GPIO_ACTIVE_LOW>; reset-delays-us = <10000>; }; c2 { reset-gpios = <&gpio0 15 GPIO_ACTIVE_LOW>; re set-delays-us = <10000>; }; The reset framework could create a reset_control backed by a gpio instead of a rcdev. I have an unfinished patch for this, but without the sharing requirement adding the reset framework abstraction between gpiod and drivers never seemed really worth it. > 2. We need to specify hold time T to reset controller in device tree > so it knows that it needs hold reset line for that long in its > implementation of reset_control_reset. Agreed. Ideally, I'd like to make this optional, and have the drivers continue to provide the hold time if they think they know it. > 3. Assuming we have 1 and 2 in place. In codec driver of c1, it can > call reset_control_reset and wait for t_a1 + t_d1. In codec driver of > c2, it can call reset_control_reset and wait for t_a2 + t_d2. The reset framework should wait for the configured assertion time, max(t_a1, t_a2). The drivers only should only have to wait for t_d1 / t_d2 after reset_control_reset returns. > We need to wait for hold time + release time because > triggered_count is increased before reset ops is called. When the > second driver finds that triggered_count is 1 and skip the real reset > operation, reset ops might just begin doing its work a short time ago. That is a good point. Maybe the reset framework should just wait for the hold time even for the second reset. Another possibility would be to serialize them with a mutex. > I am not sure whether we would need a flag in reset controller to > mark that "reset is done". When driver sees this flag is done, it can > just wait for release time instead of hold time + release time. Let's not complicate the drivers with this too much. I think reset_control_reset should guarantee that the reset line is not asserted anymore upon return. > And I found that you already solved 1 and mentioned the > possible usage of 2 in [3]. > There were discussion about letting device driver to deal with > reset-gpios by itself in [4], but it seems that reset controller can > better deal with the shared reset line situation. > Maybe we could revive the patch of GPIO support for reset controller ? The discussion with Maxime in [4] hasn't really been resolved. I still think the reset-gpios property should be kept, and the reset framework could adapt to it. This is something the device tree maintainers' input would be welcome on. > Please let me know what direction I should look into. > Thanks a lot! > > [1] http://mailman.alsa-project.org/pipermail/alsa-devel/2010-November/033246.html > https://patchwork.kernel.org/patch/9424123/ > > [2] https://patchwork.kernel.org/patch/9424123/ > > [3] https://lore.kernel.org/patchwork/patch/455839/ > > [4] https://patchwork.kernel.org/patch/3978121/ regards Philipp
On Fri, Oct 12, 2018 at 12:05:16PM +0200, Philipp Zabel wrote: > Hi Cheng-yi, > > [adding Maxime, devicetree to Cc:, the old discussion about GPIO resets > in [4] has never been resolved] > > On Tue, 2018-10-09 at 21:46 +0800, Cheng-yi Chiang wrote: > > +reset controller maintainer Philipp > > > > Hi Mark, > > Sorry for the late reply. It took me a while to investigate reset > > controller and its possible usage. I would like to figure out the > > proper way of reset handling because it is common to have a shared > > reset line for two max98927 codecs for left and right channels. > > Without supporting this usage, a simple reset-gpios change for single > > codec would not be useful, and perhaps will be duplicated if reset > > controller is a better way. > > > > Hi Philipp, > > I would like to seek your advice about whether we can use reset > > controller to support the use case where multiple devices share the > > same reset line. > > > > Let me summarize the use case: > > There are two max98927 codecs sharing the same reset line. > > The reset line is controlled by a GPIO. > > The goal is to toggle reset line once and only once. > > > > There was a similar scenario in tlv320aic3x codec driver [1]. > > A static list is used in the codec driver so probe function can know > > whether it is needed to toggle reset line. > > Mark pointed out that it is not suitable to handle the shared reset > > line inside codec driver. > > A point is that this only works for multiple devices using the same > > device driver. > > He suggested to look into reset controller so I searched through the > > usage for common reset line. > > > > Here I found a shared reset line use case [2]. > > With the patch [2], reset_control_reset can support this “reset once > > and for all” use case. > > This patch was applied as 7da33a37b48f. So the reset framework has > support for shared reset controls where only the first reset request > actually causes a reset pulse, and all others are no-ops. > > > However, I found that there are some missing pieces: > > > > Let’s assume there are two codecs c1 and c2 sharing a reset line > > controlled by GPIO. > > > > c1’s spec: > > Hold time: The minimum time to assert the reset line is t_a1. > > Release time: The minimum time to access the chip after deassert of > > the reset line is t_d1. > > > > c2’s spec: > > Hold time: The minimum time to assert the reset line is t_a2. > > Release time: The minimum time to access the chip after deassert of > > the reset line is t_d2. > > > > For both c1 and c2 to work properly, we need a reset controller that > > can assert the reset line for > > T = max(t_a1, t_a2). > > > > 1. We need reset controller to support GPIO. > > I still don't like the idea of describing a separate gpio reset > controller "device" in DT very much, as this is really just a software > abstraction, not actual hardware. For example: > > gpio_reset: reset-controller { > compatible = "gpio-reset"; > reset-gpios = <&gpio0 15 GPIO_ACTIVE_LOW>, > <&gpio1 > 16 GPIO_ACTIVE_HIGH>; > reset-delays-us = <10000>, <500>; > }; > > c1 { > resets = <&gpio_reset 0>; /* maps to <&gpio0 15 ...> */ > }; > > c2 { > resets = <&gpio_reset 0>; > }; > > What I would like better would be to let the consumers keep their reset- > gpios bindings, but add an optional hold time override in the DT: > > c1 { > reset-gpios = <&gpio0 15 GPIO_ACTIVE_LOW>; > reset-delays-us = <10000>; > }; > > c2 { > reset-gpios = <&gpio0 15 GPIO_ACTIVE_LOW>; > reset-delays-us = <10000>; > }; > > The reset framework could create a reset_control backed by a gpio > instead of a rcdev. I have an unfinished patch for this, but without the > sharing requirement adding the reset framework abstraction between gpiod > and drivers never seemed really worth it. I don't remember the exact details of our past discussion, but I (still) don't really think that this would work well. I see two main shortcomings with that approach: - I guess that the main reason you want to do that would be to have easy DT backward compatibility. Yet, the addition of the reset-delay-us would break that compatibility, since drivers that would have been converted now need to have it somehow, but older DTs wouldn't have it - There's so many variations of the reset-gpios property name that you wouldn't be able to cover all the cases anyhow, at least without breaking the compatibility (again). But I also see your point, and you're right that converting everyone to a gpio-reset node will not happen (even though I'd still really like to have that binding). What about having a function that would be called by the consumer to instantiate that reset controller from a GPIO for us, instead of trying to do it automatically? That function could take the property name that holds the GPIO, which would cover the second drawback, and the delay, which would cover the first. And in order to cover shared GPIO reset lines, we could just look at the one already created by other drivers, and if one has been created, we just give the reference to that one instead of creating it. Does that make sense? Maxime
Hi Maxime, On Fri, 2018-10-12 at 15:46 +0200, Maxime Ripard wrote: > On Fri, Oct 12, 2018 at 12:05:16PM +0200, Philipp Zabel wrote: [...] > > What I would like better would be to let the consumers keep their reset- > > gpios bindings, but add an optional hold time override in the DT: > > > > c1 { > > reset-gpios = <&gpio0 15 GPIO_ACTIVE_LOW>; > > reset-delays-us = <10000>; > > }; > > > > c2 { > > reset-gpios = <&gpio0 15 GPIO_ACTIVE_LOW>; > > reset-delays-us = <10000>; > > }; > > > > The reset framework could create a reset_control backed by a gpio > > instead of a rcdev. I have an unfinished patch for this, but without the > > sharing requirement adding the reset framework abstraction between gpiod > > and drivers never seemed really worth it. > > I don't remember the exact details of our past discussion, but I > (still) don't really think that this would work well. It has been a while :) Thanks for jumping back in. > I see two main shortcomings with that approach: > > - I guess that the main reason you want to do that would be to have > easy DT backward compatibility. Yes, that is true. The other reason is that I'd like devices to have a single binding, regardless of whether somebody decided to put them onto a board with shared reset lines. I'd find it hard to advocate for changing the thankfully common case of device-exclusive reset gpios from: some-device { reset-gpios = <&gpiox y>; }; to: rstc: reset-controller { compatible = "gpio-reset"; reset-gpios <&gpiox y>; }; some-device { resets = <&rstc 0>; }; even for new bindings. If the reset framework only supports the latter, and not the former, drivers for devices which already have reset-gpios would have to handle both reset_control and gpiod functionality, which I think should not be necessary. Note that this is not really an argument against a "gpio-reset" controller driver, but an argument for reset-gpios support integrated into the reset framework. My argument against a "gpio-reset" device node in the DT is only that it is basically a virtual device that would only be used to work around missing reset-gpios support in the reset framework. Physically, this "device" consists of no more than a few PCB traces. > Yet, the addition of the > reset-delay-us would break that compatibility, since drivers that > would have been converted now need to have it somehow, but older > DTs wouldn't have it That is why such a property would have to be optional, and the drivers would have to keep providing the reset delay themselves, as they currently do when handling GPIOs directly. It would only serve to override the driver default in case of additional delay requirements due to board specifics (such as delay elements, or shared resets). > - There's so many variations of the reset-gpios property name that > you wouldn't be able to cover all the cases anyhow, at least > without breaking the compatibility (again). This is true, and I do not have a solution for this. Especially for those cases that don't use gpiod yet. of_get_named_gpio(node, "reset-gpio") is still quite common, but I'd really like on gpiolib for polarity support. > But I also see your point, and you're right that converting everyone > to a gpio-reset node will not happen (even though I'd still really > like to have that binding). See above. I'd be a lot less reluctant to support this binding if somebody could demonstrate a real gpio controlled reset controller device of some kind. And even then I would not want to have to use this device just to connect a single GPIO with a single reset input. > What about having a function that would be called by the consumer to > instantiate that reset controller from a GPIO for us, instead of > trying to do it automatically? That function could take the property > name that holds the GPIO, which would cover the second drawback, and > the delay, which would cover the first. I like this idea. I'd like to avoid having to fall back from gpiod to of_get_named_gpio if possible, so maybe we'd have to extend gpiolib-of.c with an of_find_reset_gpio function, as is done for SPI and regulators already. We probably would have to support delay ranges. I see a lot of usleep_range calls between reset GPIO toggles in the drivers. > And in order to cover shared GPIO reset lines, we could just look at > the one already created by other drivers, and if one has been created, > we just give the reference to that one instead of creating it. > > Does that make sense? I'm not quite sure how to match an already requested reset control from the list given of_node and gpio property name at the moment - this might involve exporting gpiod_find from gpiolib, but API wise I think this is a sane proposal. I would not want to add reset controller devices for each of these GPIO reset controls, but rather store the gpio_desc reference in the reset_control instead of the rcdev reference. regards Philipp
Hi Philipp, On Thu, Oct 18, 2018 at 1:02 AM Philipp Zabel <p.zabel@pengutronix.de> wrote: > > Hi Maxime, > > On Fri, 2018-10-12 at 15:46 +0200, Maxime Ripard wrote: > > On Fri, Oct 12, 2018 at 12:05:16PM +0200, Philipp Zabel wrote: > [...] > > > What I would like better would be to let the consumers keep their reset- > > > gpios bindings, but add an optional hold time override in the DT: > > > > > > c1 { > > > reset-gpios = <&gpio0 15 GPIO_ACTIVE_LOW>; > > > reset-delays-us = <10000>; > > > }; > > > > > > c2 { > > > reset-gpios = <&gpio0 15 GPIO_ACTIVE_LOW>; > > > reset-delays-us = <10000>; > > > }; > > > > > > The reset framework could create a reset_control backed by a gpio > > > instead of a rcdev. I have an unfinished patch for this, but without the > > > sharing requirement adding the reset framework abstraction between gpiod > > > and drivers never seemed really worth it. > > > > I don't remember the exact details of our past discussion, but I > > (still) don't really think that this would work well. > > It has been a while :) Thanks for jumping back in. > > > I see two main shortcomings with that approach: > > > > - I guess that the main reason you want to do that would be to have > > easy DT backward compatibility. > > Yes, that is true. The other reason is that I'd like devices to have a > single binding, regardless of whether somebody decided to put them onto > a board with shared reset lines. > > I'd find it hard to advocate for changing the thankfully common case > of device-exclusive reset gpios from: > > some-device { > reset-gpios = <&gpiox y>; > }; > > to: > > rstc: reset-controller { > compatible = "gpio-reset"; > reset-gpios <&gpiox y>; > }; > > some-device { > resets = <&rstc 0>; > }; > > even for new bindings. > > If the reset framework only supports the latter, and not the former, > drivers for devices which already have reset-gpios would have to handle > both reset_control and gpiod functionality, which I think should not be > necessary. > > Note that this is not really an argument against a "gpio-reset" > controller driver, but an argument for reset-gpios support integrated > into the reset framework. > My argument against a "gpio-reset" device node in the DT is only that it > is basically a virtual device that would only be used to work around > missing reset-gpios support in the reset framework. Physically, this > "device" consists of no more than a few PCB traces. > > > Yet, the addition of the > > reset-delay-us would break that compatibility, since drivers that > > would have been converted now need to have it somehow, but older > > DTs wouldn't have it > > That is why such a property would have to be optional, and the drivers > would have to keep providing the reset delay themselves, as they > currently do when handling GPIOs directly. > It would only serve to override the driver default in case of additional > delay requirements due to board specifics (such as delay elements, or > shared resets). > > > - There's so many variations of the reset-gpios property name that > > you wouldn't be able to cover all the cases anyhow, at least > > without breaking the compatibility (again). > > This is true, and I do not have a solution for this. Especially for > those cases that don't use gpiod yet. > > of_get_named_gpio(node, "reset-gpio") > > is still quite common, but I'd really like on gpiolib for polarity > support. > > > But I also see your point, and you're right that converting everyone > > to a gpio-reset node will not happen (even though I'd still really > > like to have that binding). > > See above. I'd be a lot less reluctant to support this binding if > somebody could demonstrate a real gpio controlled reset controller > device of some kind. And even then I would not want to have to use > this device just to connect a single GPIO with a single reset input. > > > What about having a function that would be called by the consumer to > > instantiate that reset controller from a GPIO for us, instead of > > trying to do it automatically? That function could take the property > > name that holds the GPIO, which would cover the second drawback, and > > the delay, which would cover the first. > > I like this idea. > > I'd like to avoid having to fall back from gpiod to of_get_named_gpio if > possible, so maybe we'd have to extend gpiolib-of.c with an > of_find_reset_gpio function, as is done for SPI and regulators already. > > We probably would have to support delay ranges. I see a lot of > usleep_range calls between reset GPIO toggles in the drivers. > This looks great. I am not sure what is the plan proceeding from here. Are you going to implement this feature with the unfinished patch you mentioned to create reset_control backed by a GPIO? I am willing to help. If you have patch I can help testing it. It will be easier to test the shared reset line on my side since the board I am working now has this use case. If you don't have time for this, I can work on it based on your WIP patch. In that case could you please post the patch ? I just want to make sure I am on the right direction solving this without making duplicate efforts.. > > And in order to cover shared GPIO reset lines, we could just look at > > the one already created by other drivers, and if one has been created, > > we just give the reference to that one instead of creating it. > > > > Does that make sense? > > I'm not quite sure how to match an already requested reset control from > the list given of_node and gpio property name at the moment - this might > involve exporting gpiod_find from gpiolib, but API wise I think this is > a sane proposal. > > I would not want to add reset controller devices for each of these GPIO > reset controls, but rather store the gpio_desc reference in the > reset_control instead of the rcdev reference. This plan to support shared reset line makes sense. Thanks a lot! > > regards > Philipp
diff --git a/sound/soc/codecs/max98927.c b/sound/soc/codecs/max98927.c index 941712058a8f5..789b27cdfd9e0 100644 --- a/sound/soc/codecs/max98927.c +++ b/sound/soc/codecs/max98927.c @@ -11,6 +11,7 @@ */ #include <linux/acpi.h> +#include <linux/delay.h> #include <linux/i2c.h> #include <linux/module.h> #include <linux/regmap.h> @@ -24,6 +25,11 @@ #include <sound/tlv.h> #include "max98927.h" +#define MAX98927_MIN_RESET_US 1 +#define MAX98927_RELEASE_RESET_DELAY_US 500 + +static LIST_HEAD(reset_list); + static struct reg_default max98927_reg[] = { {MAX98927_R0001_INT_RAW1, 0x00}, {MAX98927_R0002_INT_RAW2, 0x00}, @@ -877,6 +883,54 @@ static void max98927_slot_config(struct i2c_client *i2c, max98927->i_l_slot = 1; } +static int max98927_i2c_toggle_reset(struct device *dev, + struct max98927_priv *max98927) +{ + /* + * If we do not have reset gpio, assume platform firmware + * controls the regulator and toggles it for us. + */ + if (!max98927->reset_gpio) + return 0; + + gpiod_set_value_cansleep(max98927->reset_gpio, 1); + + /* + * We need to wait a bit before we are allowed to release reset GPIO. + */ + usleep_range(MAX98927_MIN_RESET_US, MAX98927_MIN_RESET_US + 5); + + gpiod_set_value_cansleep(max98927->reset_gpio, 0); + + /* + * We need to wait a bit before I2C communication is available. + */ + usleep_range(MAX98927_RELEASE_RESET_DELAY_US, + MAX98927_RELEASE_RESET_DELAY_US + 5); + + /* + * Release reset GPIO because we are not going to use it. + */ + devm_gpiod_put(dev, max98927->reset_gpio); + + return 0; +} + +static bool max98927_is_first_to_reset(struct max98927_priv *max98927) +{ + struct max98927_priv *p; + + if (!max98927->reset_gpio) + return false; + + list_for_each_entry(p, &reset_list, list) { + if (max98927->reset_gpio == p->reset_gpio) + return false; + } + + return true; +} + static int max98927_i2c_probe(struct i2c_client *i2c, const struct i2c_device_id *id) { @@ -904,6 +958,28 @@ static int max98927_i2c_probe(struct i2c_client *i2c, } else max98927->interleave_mode = 0; + /* Gets optional GPIO for reset line. */ + max98927->reset_gpio = devm_gpiod_get_optional( + &i2c->dev, "reset", GPIOD_OUT_LOW); + if (IS_ERR(max98927->reset_gpio)) { + ret = PTR_ERR(max98927->reset_gpio); + dev_err(&i2c->dev, "error getting reset gpio: %d\n", ret); + return ret; + } + + /* + * Only toggle reset line for the first instance when the + * reset line is shared among instances. For example, + * left and right amplifier share the same reset line, and + * we should only toggle the reset line once. + */ + if (max98927_is_first_to_reset(max98927)) { + dev_info(&i2c->dev, "%s: toggle reset line\n", __func__); + ret = max98927_i2c_toggle_reset(&i2c->dev, max98927); + if (ret) + return ret; + } + /* regmap initialization */ max98927->regmap = devm_regmap_init_i2c(i2c, &max98927_regmap); @@ -934,6 +1010,8 @@ static int max98927_i2c_probe(struct i2c_client *i2c, if (ret < 0) dev_err(&i2c->dev, "Failed to register component: %d\n", ret); + list_add(&max98927->list, &reset_list); + return ret; } diff --git a/sound/soc/codecs/max98927.h b/sound/soc/codecs/max98927.h index 538992a238b28..d48f61f6c3ba5 100644 --- a/sound/soc/codecs/max98927.h +++ b/sound/soc/codecs/max98927.h @@ -275,5 +275,7 @@ struct max98927_priv { unsigned int master; unsigned int digital_gain; bool tdm_mode; + struct gpio_desc *reset_gpio; + struct list_head list; }; #endif
Toggle reset line in max98927_i2c_probe. Use a list to store max98927 instances so we do not toggle reset line again if more than one instances share the same reset line. Signed-off-by: Cheng-Yi Chiang <cychiang@chromium.org> --- sound/soc/codecs/max98927.c | 78 +++++++++++++++++++++++++++++++++++++++++++++ sound/soc/codecs/max98927.h | 2 ++ 2 files changed, 80 insertions(+)