pwm-backlight: 3.13-rc1 regression for old arm machine

pwm-backlight: 3.13-rc1 regression for old arm machine

[Robert Jarzmik]

Hi Thierry,

Since recently, and probable since last Linus's merge of PWM tree (Merge tag
'pwm/for-3.13-rc1' of
git://git.kernel.org/pub/scm/linux/kernel/git/thierry.reding/linux-pwm), my
platform has its backlight broken.

The particularity of my platform:
 - arch/arm/mach-pxa/mioa701.c
 - no device tree
 - no power supply regulator for backlight
 - backlight controlled by a PWM
 - kernel message :
[    1.495480] platform pwm-backlight: Driver pwm-backlight requests probe deferral

I think other "old" platforms will suffer from this. Do you have a
recommendation ?

Cheers.

--
Robert

pwm-backlight: 3.13-rc1 regression for old arm machine

[Thierry Reding]

On Mon, Dec 16, 2013 at 04:52:45PM +0100, Robert Jarzmik wrote:
> Hi Thierry,

Hi Robert,

Please always Cc the linux-pwm mailing list for PWM related questions.
I've done that now.

> Since recently, and probable since last Linus's merge of PWM tree (Merge tag
> 'pwm/for-3.13-rc1' of
> git://git.kernel.org/pub/scm/linux/kernel/git/thierry.reding/linux-pwm), my
> platform has its backlight broken.
> 
> The particularity of my platform:
>  - arch/arm/mach-pxa/mioa701.c
>  - no device tree
>  - no power supply regulator for backlight
>  - backlight controlled by a PWM
>  - kernel message :
> [    1.495480] platform pwm-backlight: Driver pwm-backlight requests probe deferral
> 
> I think other "old" platforms will suffer from this. Do you have a
> recommendation ?

I hadn't anticipated that =(. In fact I had been holding this patch back
for a release cycle because I was waiting for a specific regulator patch
to land which provides a dummy regulator if one wasn't specified. It
seems that that patch only works when booting from DT, though.

The correct way to fix this would be to provide a lookup table with the
dummy regulator in the board file. I've attached a patch (compile-tested
only) that might work.

If it does, please let me know and, if nobody else volunteers, I'll see
if I can come up with a set of patches to fix this for any other boards
that have the same issue.

Thierry
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pwm-backlight: 3.13-rc1 regression for old arm machine

[Robert Jarzmik]

Thierry Reding <thierry.reding@gmail.com> writes:

> I hadn't anticipated that =(. In fact I had been holding this patch back
> for a release cycle because I was waiting for a specific regulator patch
> to land which provides a dummy regulator if one wasn't specified. It
> seems that that patch only works when booting from DT, though.
>
> The correct way to fix this would be to provide a lookup table with the
> dummy regulator in the board file. I've attached a patch (compile-tested
> only) that might work.
>
> If it does, please let me know and, if nobody else volunteers, I'll see
> if I can come up with a set of patches to fix this for any other boards
> that have the same issue.
Actually, it needs a very small "tweak" to work :
-	REGULATOR_SUPPLY("power", "pwm-backlight.0"),
+	REGULATOR_SUPPLY("power", "pwm-backlight"),

Without it regulator_dev_lookup() won't match the device.

Moreover, it requires a config option, CONFIG_REGULATOR_FIXED_VOLTAGE=y. That's
not a problem for my specific platform, but I haven't seen *any* PXA platform
with it activated, which means all defconfigs have to be patched, which is
unfortunate.

As for my specific mioa701, your change with the tweak is perfectly fine and
tested.

Cheers.

--
Robert

pwm-backlight: 3.13-rc1 regression for old arm machine

[Thierry Reding]

On Tue, Dec 17, 2013 at 07:31:21PM +0100, Robert Jarzmik wrote:
> Thierry Reding <thierry.reding@gmail.com> writes:
> 
> > I hadn't anticipated that =(. In fact I had been holding this patch back
> > for a release cycle because I was waiting for a specific regulator patch
> > to land which provides a dummy regulator if one wasn't specified. It
> > seems that that patch only works when booting from DT, though.
> >
> > The correct way to fix this would be to provide a lookup table with the
> > dummy regulator in the board file. I've attached a patch (compile-tested
> > only) that might work.
> >
> > If it does, please let me know and, if nobody else volunteers, I'll see
> > if I can come up with a set of patches to fix this for any other boards
> > that have the same issue.
> Actually, it needs a very small "tweak" to work :
> -	REGULATOR_SUPPLY("power", "pwm-backlight.0"),
> +	REGULATOR_SUPPLY("power", "pwm-backlight"),
> 
> Without it regulator_dev_lookup() won't match the device.
> 
> Moreover, it requires a config option, CONFIG_REGULATOR_FIXED_VOLTAGE=y. That's
> not a problem for my specific platform,

Okay. I'll submit a patch with that tweak of yours rolled in and Haojian
can merge that via the PXA tree.

> but I haven't seen *any* PXA platform
> with it activated, which means all defconfigs have to be patched, which is
> unfortunate.

Unfortunate indeed!

> As for my specific mioa701, your change with the tweak is perfectly fine and
> tested.

Great, I'll add your Tested-by.

Thanks,
Thierry
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