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

[Thierry Reding <thierry.reding@gmail.com>]

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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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From 8c25d9b1465acd2dcd05644f2c984b54ae3dfc53 Mon Sep 17 00:00:00 2001
From: Thierry Reding <thierry.reding@gmail.com>
Date: Tue, 17 Dec 2013 10:52:36 +0100
Subject: [PATCH] ARM: pxa: Add dummy power supply for backlight for Mitac Mio
 A701

Recent changes to the pwm-backlight driver have made the power supply
mandatory. There is code in the regulator core to deal with situations
where no regulator is specified and provide a dummy, but that works on
DT-based boards only.

The situation can be remedied by adding a dummy regulator during board
initialization.

Signed-off-by: Thierry Reding <thierry.reding@gmail.com>
---
 arch/arm/mach-pxa/mioa701.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/arch/arm/mach-pxa/mioa701.c b/arch/arm/mach-pxa/mioa701.c
index f70583fee59f..5cb3a3b33772 100644
--- a/arch/arm/mach-pxa/mioa701.c
+++ b/arch/arm/mach-pxa/mioa701.c
@@ -38,6 +38,7 @@
 #include <linux/mtd/physmap.h>
 #include <linux/usb/gpio_vbus.h>
 #include <linux/reboot.h>
+#include <linux/regulator/fixed.h>
 #include <linux/regulator/max1586.h>
 #include <linux/slab.h>
 #include <linux/i2c/pxa-i2c.h>
@@ -714,6 +715,10 @@ static struct gpio global_gpios[] = {
 	{ GPIO56_MT9M111_nOE, GPIOF_OUT_INIT_LOW, "Camera nOE" },
 };
 
+static struct regulator_consumer_supply fixed_5v0_consumers[] = {
+	REGULATOR_SUPPLY("power", "pwm-backlight.0"),
+};
+
 static void __init mioa701_machine_init(void)
 {
 	int rc;
@@ -753,6 +758,10 @@ static void __init mioa701_machine_init(void)
 	pxa_set_i2c_info(&i2c_pdata);
 	pxa27x_set_i2c_power_info(NULL);
 	pxa_set_camera_info(&mioa701_pxacamera_platform_data);
+
+	regulator_register_always_on(0, "fixed-5.0V", fixed_5v0_consumers,
+				     ARRAY_SIZE(fixed_5v0_consumers),
+				     5000000);
 }
 
 static void mioa701_machine_exit(void)
-- 
1.8.4.2


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