| Message ID | 1614341544-5306-3-git-send-email-kgunda@codeaurora.org (mailing list archive) |
|---|---|
| State | Superseded, archived |
| Headers | show |
| Series | [V2,1/2] backlight: qcom-wled: Fix FSC update issue for WLED5 | expand |
On Fri, Feb 26, 2021 at 05:42:24PM +0530, Kiran Gunda wrote: > As per the current implementation, after FSC (Full Scale Current) > and brightness update the sync bits are transitioned from 1 to 0. This still seems to incorrectly describe the current behaviour. Surely in most cases (i.e. every time except the first) the value of the sync bit is 0 when the function is called and we get both a 0 to 1 and then a 1 to 0 transition. That is why I recommended set-then-clear terminology to describe the current behaviour. It is concise and correct. Daniel. > But, the FSC and brightness sync takes place during a 0 to 1 > transition of the sync bits. So the hardware team recommends a > clear-then-set approach in order to guarantee such a transition > regardless of the previous register state. > > Signed-off-by: Kiran Gunda <kgunda@codeaurora.org> > --- > drivers/video/backlight/qcom-wled.c | 12 ++++++------ > 1 file changed, 6 insertions(+), 6 deletions(-) > > diff --git a/drivers/video/backlight/qcom-wled.c b/drivers/video/backlight/qcom-wled.c > index aef52b9..19f83ac 100644 > --- a/drivers/video/backlight/qcom-wled.c > +++ b/drivers/video/backlight/qcom-wled.c > @@ -337,13 +337,13 @@ static int wled3_sync_toggle(struct wled *wled) > > rc = regmap_update_bits(wled->regmap, > wled->ctrl_addr + WLED3_SINK_REG_SYNC, > - mask, mask); > + mask, WLED3_SINK_REG_SYNC_CLEAR); > if (rc < 0) > return rc; > > rc = regmap_update_bits(wled->regmap, > wled->ctrl_addr + WLED3_SINK_REG_SYNC, > - mask, WLED3_SINK_REG_SYNC_CLEAR); > + mask, mask); > > return rc; > } > @@ -353,17 +353,17 @@ static int wled5_mod_sync_toggle(struct wled *wled) > int rc; > u8 val; > > - val = (wled->cfg.mod_sel == MOD_A) ? WLED5_SINK_REG_SYNC_MOD_A_BIT : > - WLED5_SINK_REG_SYNC_MOD_B_BIT; > rc = regmap_update_bits(wled->regmap, > wled->sink_addr + WLED5_SINK_REG_MOD_SYNC_BIT, > - WLED5_SINK_REG_SYNC_MASK, val); > + WLED5_SINK_REG_SYNC_MASK, 0); > if (rc < 0) > return rc; > > + val = (wled->cfg.mod_sel == MOD_A) ? WLED5_SINK_REG_SYNC_MOD_A_BIT : > + WLED5_SINK_REG_SYNC_MOD_B_BIT; > return regmap_update_bits(wled->regmap, > wled->sink_addr + WLED5_SINK_REG_MOD_SYNC_BIT, > - WLED5_SINK_REG_SYNC_MASK, 0); > + WLED5_SINK_REG_SYNC_MASK, val); > } > > static int wled_ovp_fault_status(struct wled *wled, bool *fault_set) > -- > The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum, > a Linux Foundation Collaborative Project >
On 2021-02-26 22:56, Daniel Thompson wrote: > On Fri, Feb 26, 2021 at 05:42:24PM +0530, Kiran Gunda wrote: >> As per the current implementation, after FSC (Full Scale Current) >> and brightness update the sync bits are transitioned from 1 to 0. > > This still seems to incorrectly describe the current behaviour. > > Surely in most cases (i.e. every time except the first) the value of > the > sync bit is 0 when the function is called and we get both a 0 to 1 > and then a 1 to 0 transition. > > That is why I recommended set-then-clear terminology to describe the > current behaviour. It is concise and correct. > > > Daniel. > > > Okay. Actually I have mentioned the "clear-and-set" in explaining the fix. Let me modify the same terminology in explaining the problem case also. >> But, the FSC and brightness sync takes place during a 0 to 1 >> transition of the sync bits. So the hardware team recommends a >> clear-then-set approach in order to guarantee such a transition >> regardless of the previous register state. >> >> Signed-off-by: Kiran Gunda <kgunda@codeaurora.org> >> --- >> drivers/video/backlight/qcom-wled.c | 12 ++++++------ >> 1 file changed, 6 insertions(+), 6 deletions(-) >> >> diff --git a/drivers/video/backlight/qcom-wled.c >> b/drivers/video/backlight/qcom-wled.c >> index aef52b9..19f83ac 100644 >> --- a/drivers/video/backlight/qcom-wled.c >> +++ b/drivers/video/backlight/qcom-wled.c >> @@ -337,13 +337,13 @@ static int wled3_sync_toggle(struct wled *wled) >> >> rc = regmap_update_bits(wled->regmap, >> wled->ctrl_addr + WLED3_SINK_REG_SYNC, >> - mask, mask); >> + mask, WLED3_SINK_REG_SYNC_CLEAR); >> if (rc < 0) >> return rc; >> >> rc = regmap_update_bits(wled->regmap, >> wled->ctrl_addr + WLED3_SINK_REG_SYNC, >> - mask, WLED3_SINK_REG_SYNC_CLEAR); >> + mask, mask); >> >> return rc; >> } >> @@ -353,17 +353,17 @@ static int wled5_mod_sync_toggle(struct wled >> *wled) >> int rc; >> u8 val; >> >> - val = (wled->cfg.mod_sel == MOD_A) ? WLED5_SINK_REG_SYNC_MOD_A_BIT : >> - WLED5_SINK_REG_SYNC_MOD_B_BIT; >> rc = regmap_update_bits(wled->regmap, >> wled->sink_addr + WLED5_SINK_REG_MOD_SYNC_BIT, >> - WLED5_SINK_REG_SYNC_MASK, val); >> + WLED5_SINK_REG_SYNC_MASK, 0); >> if (rc < 0) >> return rc; >> >> + val = (wled->cfg.mod_sel == MOD_A) ? WLED5_SINK_REG_SYNC_MOD_A_BIT : >> + WLED5_SINK_REG_SYNC_MOD_B_BIT; >> return regmap_update_bits(wled->regmap, >> wled->sink_addr + WLED5_SINK_REG_MOD_SYNC_BIT, >> - WLED5_SINK_REG_SYNC_MASK, 0); >> + WLED5_SINK_REG_SYNC_MASK, val); >> } >> >> static int wled_ovp_fault_status(struct wled *wled, bool *fault_set) >> -- >> The Qualcomm Innovation Center, Inc. is a member of the Code Aurora >> Forum, >> a Linux Foundation Collaborative Project >>
On Mon, Mar 01, 2021 at 02:15:12PM +0530, kgunda@codeaurora.org wrote: > On 2021-02-26 22:56, Daniel Thompson wrote: > > On Fri, Feb 26, 2021 at 05:42:24PM +0530, Kiran Gunda wrote: > > > As per the current implementation, after FSC (Full Scale Current) > > > and brightness update the sync bits are transitioned from 1 to 0. > > > > This still seems to incorrectly describe the current behaviour. > > > > Surely in most cases (i.e. every time except the first) the value of the > > sync bit is 0 when the function is called and we get both a 0 to 1 > > and then a 1 to 0 transition. > > > > That is why I recommended set-then-clear terminology to describe the > > current behaviour. It is concise and correct. > > Okay. Actually I have mentioned the "clear-and-set" in explaining the fix. > Let me modify the same terminology in explaining the problem case also. Yes please. In my original review I took time to explain why patch descriptions require care and attention and, also, why expressing the original behaviour as 1 to 0 was inadequate. Based on the previous feedback (and reply) I was rather surprised that the problem was only half corrected in the next revision. Daniel.
diff --git a/drivers/video/backlight/qcom-wled.c b/drivers/video/backlight/qcom-wled.c index aef52b9..19f83ac 100644 --- a/drivers/video/backlight/qcom-wled.c +++ b/drivers/video/backlight/qcom-wled.c @@ -337,13 +337,13 @@ static int wled3_sync_toggle(struct wled *wled) rc = regmap_update_bits(wled->regmap, wled->ctrl_addr + WLED3_SINK_REG_SYNC, - mask, mask); + mask, WLED3_SINK_REG_SYNC_CLEAR); if (rc < 0) return rc; rc = regmap_update_bits(wled->regmap, wled->ctrl_addr + WLED3_SINK_REG_SYNC, - mask, WLED3_SINK_REG_SYNC_CLEAR); + mask, mask); return rc; } @@ -353,17 +353,17 @@ static int wled5_mod_sync_toggle(struct wled *wled) int rc; u8 val; - val = (wled->cfg.mod_sel == MOD_A) ? WLED5_SINK_REG_SYNC_MOD_A_BIT : - WLED5_SINK_REG_SYNC_MOD_B_BIT; rc = regmap_update_bits(wled->regmap, wled->sink_addr + WLED5_SINK_REG_MOD_SYNC_BIT, - WLED5_SINK_REG_SYNC_MASK, val); + WLED5_SINK_REG_SYNC_MASK, 0); if (rc < 0) return rc; + val = (wled->cfg.mod_sel == MOD_A) ? WLED5_SINK_REG_SYNC_MOD_A_BIT : + WLED5_SINK_REG_SYNC_MOD_B_BIT; return regmap_update_bits(wled->regmap, wled->sink_addr + WLED5_SINK_REG_MOD_SYNC_BIT, - WLED5_SINK_REG_SYNC_MASK, 0); + WLED5_SINK_REG_SYNC_MASK, val); } static int wled_ovp_fault_status(struct wled *wled, bool *fault_set)
As per the current implementation, after FSC (Full Scale Current) and brightness update the sync bits are transitioned from 1 to 0. But, the FSC and brightness sync takes place during a 0 to 1 transition of the sync bits. So the hardware team recommends a clear-then-set approach in order to guarantee such a transition regardless of the previous register state. Signed-off-by: Kiran Gunda <kgunda@codeaurora.org> --- drivers/video/backlight/qcom-wled.c | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-)