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@xxxxxxxxxxx>
> 
> --- 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;
>  }
> --

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