linux-kernel - Re: [PATCH] backlight: pwm_bl: Use gpiod_get_value

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Message-ID: <20190128103835.ibgze6vbkk642dkv@flea>
Date:   Mon, 28 Jan 2019 11:38:35 +0100
From:   Maxime Ripard <maxime.ripard@...tlin.com>
To:     Chen-Yu Tsai <wens@...e.org>
Cc:     Thierry Reding <thierry.reding@...il.com>,
        Lee Jones <lee.jones@...aro.org>,
        Daniel Thompson <daniel.thompson@...aro.org>,
        Jingoo Han <jingoohan1@...il.com>, linux-pwm@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] backlight: pwm_bl: Use gpiod_get_value_cansleep() to get
 initial state

On Sun, Jan 27, 2019 at 10:50:54PM +0800, Chen-Yu Tsai wrote:
> gpiod_get_value() gives out a warning if access to the underlying gpiochip
> requires sleeping, which is common for I2C based chips:
> 
>     WARNING: CPU: 0 PID: 77 at drivers/gpio/gpiolib.c:2500 gpiod_get_value+0xd0/0x100
>     Modules linked in:
>     CPU: 0 PID: 77 Comm: kworker/0:2 Not tainted 4.14.0-rc3-00589-gf32897915d48-dirty #90
>     Hardware name: Allwinner sun4i/sun5i Families
>     Workqueue: events deferred_probe_work_func
>     [<c010ec50>] (unwind_backtrace) from [<c010b784>] (show_stack+0x10/0x14)
>     [<c010b784>] (show_stack) from [<c0797224>] (dump_stack+0x88/0x9c)
>     [<c0797224>] (dump_stack) from [<c0125b08>] (__warn+0xe8/0x100)
>     [<c0125b08>] (__warn) from [<c0125bd0>] (warn_slowpath_null+0x20/0x28)
>     [<c0125bd0>] (warn_slowpath_null) from [<c037069c>] (gpiod_get_value+0xd0/0x100)
>     [<c037069c>] (gpiod_get_value) from [<c03778d0>] (pwm_backlight_probe+0x238/0x508)
>     [<c03778d0>] (pwm_backlight_probe) from [<c0411a2c>] (platform_drv_probe+0x50/0xac)
>     [<c0411a2c>] (platform_drv_probe) from [<c0410224>] (driver_probe_device+0x238/0x2e8)
>     [<c0410224>] (driver_probe_device) from [<c040e820>] (bus_for_each_drv+0x44/0x94)
>     [<c040e820>] (bus_for_each_drv) from [<c040ff0c>] (__device_attach+0xb0/0x114)
>     [<c040ff0c>] (__device_attach) from [<c040f4f8>] (bus_probe_device+0x84/0x8c)
>     [<c040f4f8>] (bus_probe_device) from [<c040f944>] (deferred_probe_work_func+0x50/0x14c)
>     [<c040f944>] (deferred_probe_work_func) from [<c013be84>] (process_one_work+0x1ec/0x414)
>     [<c013be84>] (process_one_work) from [<c013ce5c>] (worker_thread+0x2b0/0x5a0)
>     [<c013ce5c>] (worker_thread) from [<c0141908>] (kthread+0x14c/0x154)
>     [<c0141908>] (kthread) from [<c0107ab0>] (ret_from_fork+0x14/0x24)
> 
> This was missed in commit 0c9501f823a4 ("backlight: pwm_bl: Handle gpio
> that can sleep"). The code was then moved to a separate function in
> commit 7613c922315e ("backlight: pwm_bl: Move the checks for initial power
> state to a separate function").
> 
> The only usage of gpiod_get_value() is during the probe stage, which is
> safe to sleep in. Switch to gpiod_get_value_cansleep().
> 
> Fixes: 0c9501f823a4 ("backlight: pwm_bl: Handle gpio that can sleep")
> Signed-off-by: Chen-Yu Tsai <wens@...e.org>

Acked-by: Maxime Ripard <maxime.ripard@...tlin.com>

Maxime
 
-- 
Maxime Ripard, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com

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