| Message ID | 20230503105042.453755-1-linux@rasmusvillemoes.dk (mailing list archive) |
|---|---|
| State | Accepted |
| Headers | show |
| Series | iio: addac: ad74413: don't set DIN_SINK for functions other than digital input | expand |
Hi Rasmus, Thanks for your patch... Just one comment below On Wed, 2023-05-03 at 12:50 +0200, Rasmus Villemoes wrote: > Apparently, despite the name Digital Input Configuration Register, the > settings in the DIN_CONFIGx registers also affect other channel > functions. In particular, setting a non-zero value in the DIN_SINK > field breaks the resistance measurement function. > > Now, one can of course argue that specifying a drive-strength-microamp > property along with a adi,ch-func which is not one of the digital > input functions is a bug in the device tree. However, we have a rather > complicated setup with instances of ad74412r on external hardware > modules, and have set a default drive-strength-microamp in our DT > fragments describing those, merely modifying the adi,ch-func settings > to reflect however the modules have been wired up. And restricting > this setting to just being done for digital input doesn't make the > driver any more complex. > > Fixes: 504eb485589d1 (iio: ad74413r: wire up support for drive-strength- > microamp property) > Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk> > --- > drivers/iio/addac/ad74413r.c | 11 ++++++----- > 1 file changed, 6 insertions(+), 5 deletions(-) > > diff --git a/drivers/iio/addac/ad74413r.c b/drivers/iio/addac/ad74413r.c > index e3366cf5eb31..6b0e8218f150 100644 > --- a/drivers/iio/addac/ad74413r.c > +++ b/drivers/iio/addac/ad74413r.c > @@ -1317,13 +1317,14 @@ static int ad74413r_setup_gpios(struct ad74413r_state > *st) > } > > if (config->func == CH_FUNC_DIGITAL_INPUT_LOGIC || > - config->func == CH_FUNC_DIGITAL_INPUT_LOOP_POWER) > + config->func == CH_FUNC_DIGITAL_INPUT_LOOP_POWER) { > st->comp_gpio_offsets[comp_gpio_i++] = i; > > - strength = config->drive_strength; > - ret = ad74413r_set_comp_drive_strength(st, i, strength); > - if (ret) > - return ret; > + strength = config->drive_strength; > + ret = ad74413r_set_comp_drive_strength(st, i, > strength); > + if (ret) > + return ret; > + } So, I'm not really that familiar with this part and, at this stage, I'm being lazy to check the datasheet. My concern is about breaking some other users... So, does it make any sense for having drive-strength-microamp in a non digital input at all? Can anyone have a working device by specifying that dt parameter on a non digital channel (or expect something from having that parameter set)? Or the only effect is to actually have some functions misbehaving? It feels to me (from your description) that this property is something that makes sense to be restricted and should also have that dependency stated in the bindings but it might be to late for that (as some users might have validated their devicetrees already). On the driver side, if it's never right to have these settings together, then the patch is valid since if someone has this, his configuration is broken anyways (maybe that's also a valid point for the bindings)... - Nuno Sá
On 04/05/2023 09.28, Nuno Sá wrote: > Hi Rasmus, > > So, I'm not really that familiar with this part and, at this stage, I'm being > lazy to check the datasheet. Well, the data sheet is not particularly helpful here, which is why I ended up with this mess. > My concern is about breaking some other users... I highly doubt there are users yet (other than my customer); this binding+driver implementation only just landed. > So, does it make any sense for having drive-strength-microamp in a non digital > input at all? That's the problem with the data sheet, it doesn't really say that the DIN_SINK register has any effect whatsoever when the channel function is set to something other than digital input (either flavor). Perhaps it does hint that setting it to something non-zero is probably not a good idea, because DIN_SINK is automatically set to 0 whenever the channel function is set/changed, so one needs a good reason to change DIN_SINK afterwards. We just experimentally found out that when we added the DIN_SINK to fix the digital input functions, when we got around to testing the resistance measurement function that ended up broken due to the non-zero DIN_SINK. > Can anyone have a working device by specifying that dt parameter > on a non digital channel (or expect something from having that parameter set)? > Or the only effect is to actually have some functions misbehaving? The data sheet doesn't say that the DIN_SINK should have any effect for other functions, so I'm pretty sure it's only the latter: some functions misbehave. > On the driver side, if it's never right to have > these settings together, then the patch is valid since if someone has this, his > configuration is broken anyways (maybe that's also a valid point for the > bindings)... Yes, I do believe that it's a broken description (whether or not the bindings specify that), and drivers don't need to go out of their way to validate or fixup such brokenness. But in this particular case, there's really no extra burden on the driver to not put garbage in DIN_SINK when a not-digital-input function has been chosen (the patch is a two-liner with 'git show -w'). Rasmus
On Thu, 4 May 2023 12:08:53 +0200 Rasmus Villemoes <linux@rasmusvillemoes.dk> wrote: > On 04/05/2023 09.28, Nuno Sá wrote: > > Hi Rasmus, > > > > > So, I'm not really that familiar with this part and, at this stage, I'm being > > lazy to check the datasheet. > > Well, the data sheet is not particularly helpful here, which is why I > ended up with this mess. > > > My concern is about breaking some other users... > > I highly doubt there are users yet (other than my customer); this > binding+driver implementation only just landed. > > > So, does it make any sense for having drive-strength-microamp in a non digital > > input at all? > > That's the problem with the data sheet, it doesn't really say that the > DIN_SINK register has any effect whatsoever when the channel function is > set to something other than digital input (either flavor). Perhaps it > does hint that setting it to something non-zero is probably not a good > idea, because DIN_SINK is automatically set to 0 whenever the channel > function is set/changed, so one needs a good reason to change DIN_SINK > afterwards. > > We just experimentally found out that when we added the DIN_SINK to fix > the digital input functions, when we got around to testing the > resistance measurement function that ended up broken due to the non-zero > DIN_SINK. > > > Can anyone have a working device by specifying that dt parameter > > on a non digital channel (or expect something from having that parameter set)? > > Or the only effect is to actually have some functions misbehaving? > > The data sheet doesn't say that the DIN_SINK should have any effect for > other functions, so I'm pretty sure it's only the latter: some functions > misbehave. > > > On the driver side, if it's never right to have > > these settings together, then the patch is valid since if someone has this, his > > configuration is broken anyways (maybe that's also a valid point for the > > bindings)... > > Yes, I do believe that it's a broken description (whether or not the > bindings specify that), and drivers don't need to go out of their way to > validate or fixup such brokenness. But in this particular case, there's > really no extra burden on the driver to not put garbage in DIN_SINK when > a not-digital-input function has been chosen (the patch is a two-liner > with 'git show -w'). If we can tighten the DT binding to rule out something that should not be set than that would be good. Tightening bindings is fine - we don't mind validation of bindings failing on peoples DTs as long as we didn't 'break' them actually working. Jonathan > > Rasmus >
On 06/05/2023 20.16, Jonathan Cameron wrote: > On Thu, 4 May 2023 12:08:53 +0200 > Rasmus Villemoes <linux@rasmusvillemoes.dk> wrote: > >> On 04/05/2023 09.28, Nuno Sá wrote: >>> Can anyone have a working device by specifying that dt parameter >>> on a non digital channel (or expect something from having that parameter set)? >>> Or the only effect is to actually have some functions misbehaving? >> >> The data sheet doesn't say that the DIN_SINK should have any effect for >> other functions, so I'm pretty sure it's only the latter: some functions >> misbehave. >> >>> On the driver side, if it's never right to have >>> these settings together, then the patch is valid since if someone has this, his >>> configuration is broken anyways (maybe that's also a valid point for the >>> bindings)... >> >> Yes, I do believe that it's a broken description (whether or not the >> bindings specify that), and drivers don't need to go out of their way to >> validate or fixup such brokenness. But in this particular case, there's >> really no extra burden on the driver to not put garbage in DIN_SINK when >> a not-digital-input function has been chosen (the patch is a two-liner >> with 'git show -w'). > > If we can tighten the DT binding to rule out something that should not be > set than that would be good. Tightening bindings is fine - we don't mind > validation of bindings failing on peoples DTs as long as we didn't 'break' > them actually working. Well, I'm afraid I don't have any idea how to spell that constraint in the yaml-language (help appreciated). And I assume a dt binding update would be a separate patch anyway, so could you please consider applying this patch? Thanks, Rasmus
On Mon, 22 May 2023 10:44:11 +0200 Rasmus Villemoes <linux@rasmusvillemoes.dk> wrote: > On 06/05/2023 20.16, Jonathan Cameron wrote: > > On Thu, 4 May 2023 12:08:53 +0200 > > Rasmus Villemoes <linux@rasmusvillemoes.dk> wrote: > > > >> On 04/05/2023 09.28, Nuno Sá wrote: > > >>> Can anyone have a working device by specifying that dt parameter > >>> on a non digital channel (or expect something from having that parameter set)? > >>> Or the only effect is to actually have some functions misbehaving? > >> > >> The data sheet doesn't say that the DIN_SINK should have any effect for > >> other functions, so I'm pretty sure it's only the latter: some functions > >> misbehave. > >> > >>> On the driver side, if it's never right to have > >>> these settings together, then the patch is valid since if someone has this, his > >>> configuration is broken anyways (maybe that's also a valid point for the > >>> bindings)... > >> > >> Yes, I do believe that it's a broken description (whether or not the > >> bindings specify that), and drivers don't need to go out of their way to > >> validate or fixup such brokenness. But in this particular case, there's > >> really no extra burden on the driver to not put garbage in DIN_SINK when > >> a not-digital-input function has been chosen (the patch is a two-liner > >> with 'git show -w'). > > > > If we can tighten the DT binding to rule out something that should not be > > set than that would be good. Tightening bindings is fine - we don't mind > > validation of bindings failing on peoples DTs as long as we didn't 'break' > > them actually working. > > Well, I'm afraid I don't have any idea how to spell that constraint in > the yaml-language (help appreciated). Lots of examples in tree of this sort of thing. Look for a : false with something other than additionalProperties or unevaluatedProperties Documentation/devicetree/bindings/iio/adc/adi,ad7476.yaml for example. In short you have an allOf block containing a list of rules, one of which is a match on particular conditions to set particular properties to 'false' which means that any attempt to have them set when that condition is met results in an error from the dts checking scripts. > > And I assume a dt binding update would be a separate patch anyway, so > could you please consider applying this patch? Fair enough. Applied to the fixes-togreg branch of iio.git. Thanks, Jonathan > > Thanks, > Rasmus >
diff --git a/drivers/iio/addac/ad74413r.c b/drivers/iio/addac/ad74413r.c index e3366cf5eb31..6b0e8218f150 100644 --- a/drivers/iio/addac/ad74413r.c +++ b/drivers/iio/addac/ad74413r.c @@ -1317,13 +1317,14 @@ static int ad74413r_setup_gpios(struct ad74413r_state *st) } if (config->func == CH_FUNC_DIGITAL_INPUT_LOGIC || - config->func == CH_FUNC_DIGITAL_INPUT_LOOP_POWER) + config->func == CH_FUNC_DIGITAL_INPUT_LOOP_POWER) { st->comp_gpio_offsets[comp_gpio_i++] = i; - strength = config->drive_strength; - ret = ad74413r_set_comp_drive_strength(st, i, strength); - if (ret) - return ret; + strength = config->drive_strength; + ret = ad74413r_set_comp_drive_strength(st, i, strength); + if (ret) + return ret; + } ret = ad74413r_set_gpo_config(st, i, gpo_config); if (ret)
Apparently, despite the name Digital Input Configuration Register, the settings in the DIN_CONFIGx registers also affect other channel functions. In particular, setting a non-zero value in the DIN_SINK field breaks the resistance measurement function. Now, one can of course argue that specifying a drive-strength-microamp property along with a adi,ch-func which is not one of the digital input functions is a bug in the device tree. However, we have a rather complicated setup with instances of ad74412r on external hardware modules, and have set a default drive-strength-microamp in our DT fragments describing those, merely modifying the adi,ch-func settings to reflect however the modules have been wired up. And restricting this setting to just being done for digital input doesn't make the driver any more complex. Fixes: 504eb485589d1 (iio: ad74413r: wire up support for drive-strength-microamp property) Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk> --- drivers/iio/addac/ad74413r.c | 11 ++++++----- 1 file changed, 6 insertions(+), 5 deletions(-)