[PATCH] backlight: gpio-backlight: Fix warning when the GPIO is on a I2C chip

[PATCH] backlight: gpio-backlight: Fix warning when the GPIO is on a I2C chip

[Tony Lindgren]

If the GPIO for the backlight is on an I2C chip, we currently
get nasty warnings like this during the boot:

WARNING: CPU: 0 PID: 6 at drivers/gpio/gpiolib.c:2364 gpiod_set_raw_value+0x40/0x4c()
Modules linked in:
CPU: 0 PID: 6 Comm: kworker/u2:0 Not tainted 3.15.0-rc4-12393-gcde9f4e #400
Workqueue: deferwq deferred_probe_work_func
[<c0014cbc>] (unwind_backtrace) from [<c001191c>] (show_stack+0x10/0x14)
[<c001191c>] (show_stack) from [<c0566ae0>] (dump_stack+0x80/0x9c)
[<c0566ae0>] (dump_stack) from [<c003f61c>] (warn_slowpath_common+0x68/0x8c)
[<c003f61c>] (warn_slowpath_common) from [<c003f65c>] (warn_slowpath_null+0x1c/0x24)
[<c003f65c>] (warn_slowpath_null) from [<c02f7e10>] (gpiod_set_raw_value+0x40/0x4c)
[<c02f7e10>] (gpiod_set_raw_value) from [<c0308fbc>] (gpio_backlight_update_status+0x4c/0x74)
[<c0308fbc>] (gpio_backlight_update_status) from [<c030914c>] (gpio_backlight_probe+0x168/0x254)
[<c030914c>] (gpio_backlight_probe) from [<c0378fa8>] (platform_drv_probe+0x18/0x48)
[<c0378fa8>] (platform_drv_probe) from [<c0377c40>] (driver_probe_device+0x10c/0x238)
[<c0377c40>] (driver_probe_device) from [<c0376330>] (bus_for_each_drv+0x44/0x8c)
[<c0376330>] (bus_for_each_drv) from [<c0377afc>] (device_attach+0x74/0x8c)
[<c0377afc>] (device_attach) from [<c03771c4>] (bus_probe_device+0x88/0xb0)
[<c03771c4>] (bus_probe_device) from [<c03775c8>] (deferred_probe_work_func+0x64/0x94)
[<c03775c8>] (deferred_probe_work_func) from [<c00572e8>] (process_one_work+0x1b4/0x4bc)
[<c00572e8>] (process_one_work) from [<c00579d0>] (worker_thread+0x11c/0x398)
[<c00579d0>] (worker_thread) from [<c005dfd8>] (kthread+0xc8/0xe4)
[<c005dfd8>] (kthread) from [<c000e768>] (ret_from_fork+0x14/0x2c)

Fix this by using gpio_set_value_cansleep() as suggested in
drivers/gpio/gpiolib.c:2364. This is what the other backlight drivers
are also doing.

Signed-off-by: Tony Lindgren <tony@atomide.com>

--- a/drivers/video/backlight/gpio_backlight.c
+++ b/drivers/video/backlight/gpio_backlight.c
@@ -38,7 +38,8 @@ static int gpio_backlight_update_status(struct backlight_device *bl)
 	    bl->props.state & (BL_CORE_SUSPENDED | BL_CORE_FBBLANK))
 		brightness = 0;
 
-	gpio_set_value(gbl->gpio, brightness ? gbl->active : !gbl->active);
+	gpio_set_value_cansleep(gbl->gpio,
+				brightness ? gbl->active : !gbl->active);
 
 	return 0;
 }

Re: [PATCH] backlight: gpio-backlight: Fix warning when the GPIO is on a I2C chip

[Jingoo Han]

On Friday, May 09, 2014 10:25 AM, Lee Jones wrote:
> 
> If the GPIO for the backlight is on an I2C chip, we currently
> get nasty warnings like this during the boot:
> 
> WARNING: CPU: 0 PID: 6 at drivers/gpio/gpiolib.c:2364 gpiod_set_raw_value+0x40/0x4c()
> Modules linked in:
> CPU: 0 PID: 6 Comm: kworker/u2:0 Not tainted 3.15.0-rc4-12393-gcde9f4e #400
> Workqueue: deferwq deferred_probe_work_func
> [<c0014cbc>] (unwind_backtrace) from [<c001191c>] (show_stack+0x10/0x14)
> [<c001191c>] (show_stack) from [<c0566ae0>] (dump_stack+0x80/0x9c)
> [<c0566ae0>] (dump_stack) from [<c003f61c>] (warn_slowpath_common+0x68/0x8c)
> [<c003f61c>] (warn_slowpath_common) from [<c003f65c>] (warn_slowpath_null+0x1c/0x24)
> [<c003f65c>] (warn_slowpath_null) from [<c02f7e10>] (gpiod_set_raw_value+0x40/0x4c)
> [<c02f7e10>] (gpiod_set_raw_value) from [<c0308fbc>] (gpio_backlight_update_status+0x4c/0x74)
> [<c0308fbc>] (gpio_backlight_update_status) from [<c030914c>] (gpio_backlight_probe+0x168/0x254)
> [<c030914c>] (gpio_backlight_probe) from [<c0378fa8>] (platform_drv_probe+0x18/0x48)
> [<c0378fa8>] (platform_drv_probe) from [<c0377c40>] (driver_probe_device+0x10c/0x238)
> [<c0377c40>] (driver_probe_device) from [<c0376330>] (bus_for_each_drv+0x44/0x8c)
> [<c0376330>] (bus_for_each_drv) from [<c0377afc>] (device_attach+0x74/0x8c)
> [<c0377afc>] (device_attach) from [<c03771c4>] (bus_probe_device+0x88/0xb0)
> [<c03771c4>] (bus_probe_device) from [<c03775c8>] (deferred_probe_work_func+0x64/0x94)
> [<c03775c8>] (deferred_probe_work_func) from [<c00572e8>] (process_one_work+0x1b4/0x4bc)
> [<c00572e8>] (process_one_work) from [<c00579d0>] (worker_thread+0x11c/0x398)
> [<c00579d0>] (worker_thread) from [<c005dfd8>] (kthread+0xc8/0xe4)
> [<c005dfd8>] (kthread) from [<c000e768>] (ret_from_fork+0x14/0x2c)
> 
> Fix this by using gpio_set_value_cansleep() as suggested in
> drivers/gpio/gpiolib.c:2364. This is what the other backlight drivers
> are also doing.

OK, I see.
However, gpio_backlight drive can be used by a lot of gpio drivers.
In some cases, 'can_sleep' is 'false' and gpio_set_value_cansleep()
is unnecessary.

In my opinion, gpio_set_value_cansleep() or gpio_set_value() can be
called selectively by 'can_sleep' value.

How about the following?

-       gpio_set_value(gbl->gpio, brightness ? gbl->active : !gbl->active);
+       if (gpio_cansleep(gbl->gpio))
+               gpio_set_value_cansleep(gbl->gpio,
+                                       brightness ? gbl->active : !gbl->active);
+       else
+               gpio_set_value(gbl->gpio, brightness ? gbl->active : !gbl->active);

Best regards,
Jingoo Han

> 
> Signed-off-by: Tony Lindgren <tony@atomide.com>
> 
> --- a/drivers/video/backlight/gpio_backlight.c
> +++ b/drivers/video/backlight/gpio_backlight.c
> @@ -38,7 +38,8 @@ static int gpio_backlight_update_status(struct backlight_device *bl)
>  	    bl->props.state & (BL_CORE_SUSPENDED | BL_CORE_FBBLANK))
>  		brightness = 0;
> 
> -	gpio_set_value(gbl->gpio, brightness ? gbl->active : !gbl->active);
> +	gpio_set_value_cansleep(gbl->gpio,
> +				brightness ? gbl->active : !gbl->active);
> 
>  	return 0;
>  }
> --

Re: [PATCH] backlight: gpio-backlight: Fix warning when the GPIO is on a I2C chip

[Tony Lindgren]

* Jingoo Han <jg1.han@samsung.com> [140508 19:25]:
> On Friday, May 09, 2014 10:25 AM, Lee Jones wrote:
> > 
> > If the GPIO for the backlight is on an I2C chip, we currently
> > get nasty warnings like this during the boot:
> > 
> > WARNING: CPU: 0 PID: 6 at drivers/gpio/gpiolib.c:2364 gpiod_set_raw_value+0x40/0x4c()
> > Modules linked in:
> > CPU: 0 PID: 6 Comm: kworker/u2:0 Not tainted 3.15.0-rc4-12393-gcde9f4e #400
> > Workqueue: deferwq deferred_probe_work_func
> > [<c0014cbc>] (unwind_backtrace) from [<c001191c>] (show_stack+0x10/0x14)
> > [<c001191c>] (show_stack) from [<c0566ae0>] (dump_stack+0x80/0x9c)
> > [<c0566ae0>] (dump_stack) from [<c003f61c>] (warn_slowpath_common+0x68/0x8c)
> > [<c003f61c>] (warn_slowpath_common) from [<c003f65c>] (warn_slowpath_null+0x1c/0x24)
> > [<c003f65c>] (warn_slowpath_null) from [<c02f7e10>] (gpiod_set_raw_value+0x40/0x4c)
> > [<c02f7e10>] (gpiod_set_raw_value) from [<c0308fbc>] (gpio_backlight_update_status+0x4c/0x74)
> > [<c0308fbc>] (gpio_backlight_update_status) from [<c030914c>] (gpio_backlight_probe+0x168/0x254)
> > [<c030914c>] (gpio_backlight_probe) from [<c0378fa8>] (platform_drv_probe+0x18/0x48)
> > [<c0378fa8>] (platform_drv_probe) from [<c0377c40>] (driver_probe_device+0x10c/0x238)
> > [<c0377c40>] (driver_probe_device) from [<c0376330>] (bus_for_each_drv+0x44/0x8c)
> > [<c0376330>] (bus_for_each_drv) from [<c0377afc>] (device_attach+0x74/0x8c)
> > [<c0377afc>] (device_attach) from [<c03771c4>] (bus_probe_device+0x88/0xb0)
> > [<c03771c4>] (bus_probe_device) from [<c03775c8>] (deferred_probe_work_func+0x64/0x94)
> > [<c03775c8>] (deferred_probe_work_func) from [<c00572e8>] (process_one_work+0x1b4/0x4bc)
> > [<c00572e8>] (process_one_work) from [<c00579d0>] (worker_thread+0x11c/0x398)
> > [<c00579d0>] (worker_thread) from [<c005dfd8>] (kthread+0xc8/0xe4)
> > [<c005dfd8>] (kthread) from [<c000e768>] (ret_from_fork+0x14/0x2c)
> > 
> > Fix this by using gpio_set_value_cansleep() as suggested in
> > drivers/gpio/gpiolib.c:2364. This is what the other backlight drivers
> > are also doing.
> 
> OK, I see.
> However, gpio_backlight drive can be used by a lot of gpio drivers.
> In some cases, 'can_sleep' is 'false' and gpio_set_value_cansleep()
> is unnecessary.
> 
> In my opinion, gpio_set_value_cansleep() or gpio_set_value() can be
> called selectively by 'can_sleep' value.
> 
> How about the following?
> 
> -       gpio_set_value(gbl->gpio, brightness ? gbl->active : !gbl->active);
> +       if (gpio_cansleep(gbl->gpio))
> +               gpio_set_value_cansleep(gbl->gpio,
> +                                       brightness ? gbl->active : !gbl->active);
> +       else
> +               gpio_set_value(gbl->gpio, brightness ? gbl->active : !gbl->active);

It should be always fine to use gpio_set_value_cansleep(), see your
old thread from few years ago related to another backlight driver:

https://lkml.org/lkml/2012/12/5/343

Regards,

Tony

Re: [PATCH] backlight: gpio-backlight: Fix warning when the GPIO is on a I2C chip

[Jingoo Han]

On Friday, May 09, 2014 12:09 PM, Tony Lindgren wrote:
> On Friday, May 09, 2014 11:25 AM, Jingoo Han wrote:
> > On Friday, May 09, 2014 10:25 AM, Lee Jones wrote:
> > >
> > > If the GPIO for the backlight is on an I2C chip, we currently
> > > get nasty warnings like this during the boot:
> > >
> > > WARNING: CPU: 0 PID: 6 at drivers/gpio/gpiolib.c:2364 gpiod_set_raw_value+0x40/0x4c()
> > > Modules linked in:
> > > CPU: 0 PID: 6 Comm: kworker/u2:0 Not tainted 3.15.0-rc4-12393-gcde9f4e #400
> > > Workqueue: deferwq deferred_probe_work_func
> > > [<c0014cbc>] (unwind_backtrace) from [<c001191c>] (show_stack+0x10/0x14)
> > > [<c001191c>] (show_stack) from [<c0566ae0>] (dump_stack+0x80/0x9c)
> > > [<c0566ae0>] (dump_stack) from [<c003f61c>] (warn_slowpath_common+0x68/0x8c)
> > > [<c003f61c>] (warn_slowpath_common) from [<c003f65c>] (warn_slowpath_null+0x1c/0x24)
> > > [<c003f65c>] (warn_slowpath_null) from [<c02f7e10>] (gpiod_set_raw_value+0x40/0x4c)
> > > [<c02f7e10>] (gpiod_set_raw_value) from [<c0308fbc>] (gpio_backlight_update_status+0x4c/0x74)
> > > [<c0308fbc>] (gpio_backlight_update_status) from [<c030914c>] (gpio_backlight_probe+0x168/0x254)
> > > [<c030914c>] (gpio_backlight_probe) from [<c0378fa8>] (platform_drv_probe+0x18/0x48)
> > > [<c0378fa8>] (platform_drv_probe) from [<c0377c40>] (driver_probe_device+0x10c/0x238)
> > > [<c0377c40>] (driver_probe_device) from [<c0376330>] (bus_for_each_drv+0x44/0x8c)
> > > [<c0376330>] (bus_for_each_drv) from [<c0377afc>] (device_attach+0x74/0x8c)
> > > [<c0377afc>] (device_attach) from [<c03771c4>] (bus_probe_device+0x88/0xb0)
> > > [<c03771c4>] (bus_probe_device) from [<c03775c8>] (deferred_probe_work_func+0x64/0x94)
> > > [<c03775c8>] (deferred_probe_work_func) from [<c00572e8>] (process_one_work+0x1b4/0x4bc)
> > > [<c00572e8>] (process_one_work) from [<c00579d0>] (worker_thread+0x11c/0x398)
> > > [<c00579d0>] (worker_thread) from [<c005dfd8>] (kthread+0xc8/0xe4)
> > > [<c005dfd8>] (kthread) from [<c000e768>] (ret_from_fork+0x14/0x2c)
> > >
> > > Fix this by using gpio_set_value_cansleep() as suggested in
> > > drivers/gpio/gpiolib.c:2364. This is what the other backlight drivers
> > > are also doing.
> >
> > OK, I see.
> > However, gpio_backlight drive can be used by a lot of gpio drivers.
> > In some cases, 'can_sleep' is 'false' and gpio_set_value_cansleep()
> > is unnecessary.
> >
> > In my opinion, gpio_set_value_cansleep() or gpio_set_value() can be
> > called selectively by 'can_sleep' value.
> >
> > How about the following?
> >
> > -       gpio_set_value(gbl->gpio, brightness ? gbl->active : !gbl->active);
> > +       if (gpio_cansleep(gbl->gpio))
> > +               gpio_set_value_cansleep(gbl->gpio,
> > +                                       brightness ? gbl->active : !gbl->active);
> > +       else
> > +               gpio_set_value(gbl->gpio, brightness ? gbl->active : !gbl->active);
> 
> It should be always fine to use gpio_set_value_cansleep(), see your
> old thread from few years ago related to another backlight driver:
> 
> https://lkml.org/lkml/2012/12/5/343

(+cc Linus Walleij, Alexandre Courbot, Russell King)

OK, I see.

gpio_set_value_cansleep() calls gpiod_set_raw_value_cansleep(),
and gpio_set_value() calls gpiod_set_raw_value() as below.

./drivers/gpio/gpiolib.c
void gpiod_set_raw_value_cansleep(struct gpio_desc *desc, int value)
{
        might_sleep_if(extra_checks);
        if (!desc)
                return;
        _gpiod_set_raw_value(desc, value);
}
EXPORT_SYMBOL_GPL(gpiod_set_raw_value_cansleep);

./drivers/gpio/gpiolib.c
void gpiod_set_raw_value(struct gpio_desc *desc, int value)
{
        if (!desc)
                return;
        /* Should be using gpio_set_value_cansleep() */
        WARN_ON(desc->chip->can_sleep);
        _gpiod_set_raw_value(desc, value);
}
EXPORT_SYMBOL_GPL(gpiod_set_raw_value);

Then, the difference between gpio_set_value_cansleep() or
gpio_set_value() is whether might_sleep_if(extra_checks) is
called or not.

So, you said that "It should be always fine to use 
gpio_set_value_cansleep()", right?

Linus Walleij,
Is there any reason to keep these two functions such as
gpiod_set_raw_value_cansleep() and gpiod_set_raw_value()?

Best regards,
Jingoo Han

Re: [PATCH] backlight: gpio-backlight: Fix warning when the GPIO is on a I2C chip

[Linus Walleij]

On Fri, May 9, 2014 at 5:42 AM, Jingoo Han <jg1.han@samsung.com> wrote:

> Linus Walleij,
> Is there any reason to keep these two functions such as
> gpiod_set_raw_value_cansleep() and gpiod_set_raw_value()?

Yes, the former can *not* be called from interrupt context,
and thus erroneous usage can be detected with runtime checks.

Yours,
Linus Walleij

Re: [PATCH] backlight: gpio-backlight: Fix warning when the GPIO is on a I2C chip

[Jingoo Han]

On Friday, May 09, 2014 10:25 AM, Tony Lindgren wrote:
> 
> If the GPIO for the backlight is on an I2C chip, we currently
> get nasty warnings like this during the boot:
> 
> WARNING: CPU: 0 PID: 6 at drivers/gpio/gpiolib.c:2364 gpiod_set_raw_value+0x40/0x4c()
> Modules linked in:
> CPU: 0 PID: 6 Comm: kworker/u2:0 Not tainted 3.15.0-rc4-12393-gcde9f4e #400
> Workqueue: deferwq deferred_probe_work_func
> [<c0014cbc>] (unwind_backtrace) from [<c001191c>] (show_stack+0x10/0x14)
> [<c001191c>] (show_stack) from [<c0566ae0>] (dump_stack+0x80/0x9c)
> [<c0566ae0>] (dump_stack) from [<c003f61c>] (warn_slowpath_common+0x68/0x8c)
> [<c003f61c>] (warn_slowpath_common) from [<c003f65c>] (warn_slowpath_null+0x1c/0x24)
> [<c003f65c>] (warn_slowpath_null) from [<c02f7e10>] (gpiod_set_raw_value+0x40/0x4c)
> [<c02f7e10>] (gpiod_set_raw_value) from [<c0308fbc>] (gpio_backlight_update_status+0x4c/0x74)
> [<c0308fbc>] (gpio_backlight_update_status) from [<c030914c>] (gpio_backlight_probe+0x168/0x254)
> [<c030914c>] (gpio_backlight_probe) from [<c0378fa8>] (platform_drv_probe+0x18/0x48)
> [<c0378fa8>] (platform_drv_probe) from [<c0377c40>] (driver_probe_device+0x10c/0x238)
> [<c0377c40>] (driver_probe_device) from [<c0376330>] (bus_for_each_drv+0x44/0x8c)
> [<c0376330>] (bus_for_each_drv) from [<c0377afc>] (device_attach+0x74/0x8c)
> [<c0377afc>] (device_attach) from [<c03771c4>] (bus_probe_device+0x88/0xb0)
> [<c03771c4>] (bus_probe_device) from [<c03775c8>] (deferred_probe_work_func+0x64/0x94)
> [<c03775c8>] (deferred_probe_work_func) from [<c00572e8>] (process_one_work+0x1b4/0x4bc)
> [<c00572e8>] (process_one_work) from [<c00579d0>] (worker_thread+0x11c/0x398)
> [<c00579d0>] (worker_thread) from [<c005dfd8>] (kthread+0xc8/0xe4)
> [<c005dfd8>] (kthread) from [<c000e768>] (ret_from_fork+0x14/0x2c)
> 
> Fix this by using gpio_set_value_cansleep() as suggested in
> drivers/gpio/gpiolib.c:2364. This is what the other backlight drivers
> are also doing.
> 
> Signed-off-by: Tony Lindgren <tony@atomide.com>

(+cc Linus Walleij, Alexandre Courbot, Russell King)

Hi Lee Jones,

Would you apply this patch into backlight git tree?
If you have other opinions, please let us know. :-)
Thank you.

Acked-by: Jingoo Han <jg1.han@samsung.com>

Best regards,
Jingoo Han

> 
> --- a/drivers/video/backlight/gpio_backlight.c
> +++ b/drivers/video/backlight/gpio_backlight.c
> @@ -38,7 +38,8 @@ static int gpio_backlight_update_status(struct backlight_device *bl)
>  	    bl->props.state & (BL_CORE_SUSPENDED | BL_CORE_FBBLANK))
>  		brightness = 0;
> 
> -	gpio_set_value(gbl->gpio, brightness ? gbl->active : !gbl->active);
> +	gpio_set_value_cansleep(gbl->gpio,
> +				brightness ? gbl->active : !gbl->active);
> 
>  	return 0;
>  }

Re: [PATCH] backlight: gpio-backlight: Fix warning when the GPIO is on a I2C chip

[Lee Jones]

> If the GPIO for the backlight is on an I2C chip, we currently
> get nasty warnings like this during the boot:
> 
> WARNING: CPU: 0 PID: 6 at drivers/gpio/gpiolib.c:2364 gpiod_set_raw_value+0x40/0x4c()
> Modules linked in:
> CPU: 0 PID: 6 Comm: kworker/u2:0 Not tainted 3.15.0-rc4-12393-gcde9f4e #400
> Workqueue: deferwq deferred_probe_work_func
> [<c0014cbc>] (unwind_backtrace) from [<c001191c>] (show_stack+0x10/0x14)
> [<c001191c>] (show_stack) from [<c0566ae0>] (dump_stack+0x80/0x9c)
> [<c0566ae0>] (dump_stack) from [<c003f61c>] (warn_slowpath_common+0x68/0x8c)
> [<c003f61c>] (warn_slowpath_common) from [<c003f65c>] (warn_slowpath_null+0x1c/0x24)
> [<c003f65c>] (warn_slowpath_null) from [<c02f7e10>] (gpiod_set_raw_value+0x40/0x4c)
> [<c02f7e10>] (gpiod_set_raw_value) from [<c0308fbc>] (gpio_backlight_update_status+0x4c/0x74)
> [<c0308fbc>] (gpio_backlight_update_status) from [<c030914c>] (gpio_backlight_probe+0x168/0x254)
> [<c030914c>] (gpio_backlight_probe) from [<c0378fa8>] (platform_drv_probe+0x18/0x48)
> [<c0378fa8>] (platform_drv_probe) from [<c0377c40>] (driver_probe_device+0x10c/0x238)
> [<c0377c40>] (driver_probe_device) from [<c0376330>] (bus_for_each_drv+0x44/0x8c)
> [<c0376330>] (bus_for_each_drv) from [<c0377afc>] (device_attach+0x74/0x8c)
> [<c0377afc>] (device_attach) from [<c03771c4>] (bus_probe_device+0x88/0xb0)
> [<c03771c4>] (bus_probe_device) from [<c03775c8>] (deferred_probe_work_func+0x64/0x94)
> [<c03775c8>] (deferred_probe_work_func) from [<c00572e8>] (process_one_work+0x1b4/0x4bc)
> [<c00572e8>] (process_one_work) from [<c00579d0>] (worker_thread+0x11c/0x398)
> [<c00579d0>] (worker_thread) from [<c005dfd8>] (kthread+0xc8/0xe4)
> [<c005dfd8>] (kthread) from [<c000e768>] (ret_from_fork+0x14/0x2c)
> 
> Fix this by using gpio_set_value_cansleep() as suggested in
> drivers/gpio/gpiolib.c:2364. This is what the other backlight drivers
> are also doing.
> 
> Signed-off-by: Tony Lindgren <tony@atomide.com>

Applied, thanks.

-- 
Lee Jones
Linaro STMicroelectronics Landing Team Lead
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