[v6,1/5] pwm-backlight: enable/disable the PWM before/after LCD enable toggle.

Message ID 20180326095213.18362-1-enric.balletbo@collabora.com
State Not Applicable
Headers show
Series
  • [v6,1/5] pwm-backlight: enable/disable the PWM before/after LCD enable toggle.
Related show

Commit Message

Enric Balletbo i Serra March 26, 2018, 9:52 a.m.
Before this patch the enable signal was set before the PWM signal and
vice-versa on power off. This sequence is wrong, at least, it is on
the different panels datasheets that I checked, so I inverted the sequence
to follow the specs.

For reference the following panels have the mentioned sequence:
  - N133HSE-EA1 (Innolux)
  - N116BGE (Innolux)
  - N156BGE-L21 (Innolux)
  - B101EAN0 (Auo)
  - B101AW03 (Auo)
  - LTN101NT05 (Samsung)
  - CLAA101WA01A (Chunghwa)

Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>
Acked-by: Daniel Thompson <daniel.thompson@linaro.org>
Acked-by: Jingoo Han <jingoohan1@gmail.com>
Acked-by: Thierry Reding <thierry.reding@gmail.com>
---
Changes since v5:
 - Add Acked-by: Thierry Reding <thierry.reding@gmail.com>
Changes since v4:
 - Rebase on top of mainline.
 - Add the acks from Daniel Thompson and Jingoo Han.
Changes since v3:
 - List the part numbers for the panel checked (Daniel Thompson)
Changes since v2:
 - Add this as a separate patch (Thierry Reding)
Changes since v1:
 - None
---
 drivers/video/backlight/pwm_bl.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

Comments

Pavel Machek March 26, 2018, 10:42 a.m. | #1
On Mon 2018-03-26 11:52:09, Enric Balletbo i Serra wrote:
> Before this patch the enable signal was set before the PWM signal and
> vice-versa on power off. This sequence is wrong, at least, it is on
> the different panels datasheets that I checked, so I inverted the sequence
> to follow the specs.
> 
> For reference the following panels have the mentioned sequence:
>   - N133HSE-EA1 (Innolux)
>   - N116BGE (Innolux)
>   - N156BGE-L21 (Innolux)
>   - B101EAN0 (Auo)
>   - B101AW03 (Auo)
>   - LTN101NT05 (Samsung)
>   - CLAA101WA01A (Chunghwa)

Ok, but this changes behaviour for other panels, too. Are you sure you
are not breaking one of those?
								Pavel
Enric Balletbo Serra March 26, 2018, 2:40 p.m. | #2
Hi Pavel,

2018-03-26 12:42 GMT+02:00 Pavel Machek <pavel@ucw.cz>:
> On Mon 2018-03-26 11:52:09, Enric Balletbo i Serra wrote:
>> Before this patch the enable signal was set before the PWM signal and
>> vice-versa on power off. This sequence is wrong, at least, it is on
>> the different panels datasheets that I checked, so I inverted the sequence
>> to follow the specs.
>>
>> For reference the following panels have the mentioned sequence:
>>   - N133HSE-EA1 (Innolux)
>>   - N116BGE (Innolux)
>>   - N156BGE-L21 (Innolux)
>>   - B101EAN0 (Auo)
>>   - B101AW03 (Auo)
>>   - LTN101NT05 (Samsung)
>>   - CLAA101WA01A (Chunghwa)
>
> Ok, but this changes behaviour for other panels, too. Are you sure you
> are not breaking one of those?

I can't say that I am 100% sure because I didn't find all the
datasheets of all the panels supported in the kernel. But all the
datasheets I checked specifies this sequence as valid. In general I
think that doesn't really matter, but I know that at least the
B116XTN02 panel requires enable first the PWM, wait 10ms and then
enable BL_EN to avoid garbage. So the other way around is not valid
for this panel. That's the reason for this patchset.

If anyone knows a panel that says the contrary, please let me know and
I'll try to rework the patches to satisfy both requirements.

Regards,
 Enric


>                                                                 Pavel
>
> --
> (english) http://www.livejournal.com/~pavelmachek
> (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
--
To unsubscribe from this list: send the line "unsubscribe linux-pwm" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Daniel Thompson March 26, 2018, 3:18 p.m. | #3
On Mon, Mar 26, 2018 at 04:40:21PM +0200, Enric Balletbo Serra wrote:
> Hi Pavel,
> 
> 2018-03-26 12:42 GMT+02:00 Pavel Machek <pavel@ucw.cz>:
> > On Mon 2018-03-26 11:52:09, Enric Balletbo i Serra wrote:
> >> Before this patch the enable signal was set before the PWM signal and
> >> vice-versa on power off. This sequence is wrong, at least, it is on
> >> the different panels datasheets that I checked, so I inverted the sequence
> >> to follow the specs.
> >>
> >> For reference the following panels have the mentioned sequence:
> >>   - N133HSE-EA1 (Innolux)
> >>   - N116BGE (Innolux)
> >>   - N156BGE-L21 (Innolux)
> >>   - B101EAN0 (Auo)
> >>   - B101AW03 (Auo)
> >>   - LTN101NT05 (Samsung)
> >>   - CLAA101WA01A (Chunghwa)
> >
> > Ok, but this changes behaviour for other panels, too. Are you sure you
> > are not breaking one of those?
> 
> I can't say that I am 100% sure because I didn't find all the
> datasheets of all the panels supported in the kernel. But all the
> datasheets I checked specifies this sequence as valid. In general I
> think that doesn't really matter, but I know that at least the
> B116XTN02 panel requires enable first the PWM, wait 10ms and then
> enable BL_EN to avoid garbage. So the other way around is not valid
> for this panel. That's the reason for this patchset.

This is certainly a patch that could cause regressions... but it would
be a very odd panel that *likes* to be exposed to all the weird edges
that might occur whilst the PWM stablizes and a panel that *needs* to
see weird edges to work seems even less likely (since it could act
different with each SoC).

So whilst the patch is not absolutely cast iron guaranteed free of
risk, I think it is well enough argued for.

Naturally I may change my position *very* quickly on receipt of the
first bug report ;-)


Daniel.
--
To unsubscribe from this list: send the line "unsubscribe linux-pwm" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Lee Jones March 28, 2018, 11:12 a.m. | #4
On Mon, 26 Mar 2018, Enric Balletbo i Serra wrote:

> Before this patch the enable signal was set before the PWM signal and
> vice-versa on power off. This sequence is wrong, at least, it is on
> the different panels datasheets that I checked, so I inverted the sequence
> to follow the specs.
> 
> For reference the following panels have the mentioned sequence:
>   - N133HSE-EA1 (Innolux)
>   - N116BGE (Innolux)
>   - N156BGE-L21 (Innolux)
>   - B101EAN0 (Auo)
>   - B101AW03 (Auo)
>   - LTN101NT05 (Samsung)
>   - CLAA101WA01A (Chunghwa)
> 
> Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>
> Acked-by: Daniel Thompson <daniel.thompson@linaro.org>
> Acked-by: Jingoo Han <jingoohan1@gmail.com>
> Acked-by: Thierry Reding <thierry.reding@gmail.com>
> ---
> Changes since v5:
>  - Add Acked-by: Thierry Reding <thierry.reding@gmail.com>
> Changes since v4:
>  - Rebase on top of mainline.
>  - Add the acks from Daniel Thompson and Jingoo Han.
> Changes since v3:
>  - List the part numbers for the panel checked (Daniel Thompson)
> Changes since v2:
>  - Add this as a separate patch (Thierry Reding)
> Changes since v1:
>  - None
> ---
>  drivers/video/backlight/pwm_bl.c | 9 +++++----
>  1 file changed, 5 insertions(+), 4 deletions(-)

Enric,

Please collect all of your Acks and submit a RESEND.

I will then apply the set.

Patch

diff --git a/drivers/video/backlight/pwm_bl.c b/drivers/video/backlight/pwm_bl.c
index 1c2289ddd555..698ec68bcdc9 100644
--- a/drivers/video/backlight/pwm_bl.c
+++ b/drivers/video/backlight/pwm_bl.c
@@ -54,10 +54,11 @@  static void pwm_backlight_power_on(struct pwm_bl_data *pb, int brightness)
 	if (err < 0)
 		dev_err(pb->dev, "failed to enable power supply\n");
 
+	pwm_enable(pb->pwm);
+
 	if (pb->enable_gpio)
 		gpiod_set_value_cansleep(pb->enable_gpio, 1);
 
-	pwm_enable(pb->pwm);
 	pb->enabled = true;
 }
 
@@ -66,12 +67,12 @@  static void pwm_backlight_power_off(struct pwm_bl_data *pb)
 	if (!pb->enabled)
 		return;
 
-	pwm_config(pb->pwm, 0, pb->period);
-	pwm_disable(pb->pwm);
-
 	if (pb->enable_gpio)
 		gpiod_set_value_cansleep(pb->enable_gpio, 0);
 
+	pwm_config(pb->pwm, 0, pb->period);
+	pwm_disable(pb->pwm);
+
 	regulator_disable(pb->power_supply);
 	pb->enabled = false;
 }