linux-kernel - Re: [PATCH] backlight: pwm_bl: Fix GPIO out for unimplemented .get

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Date:   Fri, 24 Mar 2017 16:43:44 +0000
From:   Daniel Thompson <daniel.thompson@...aro.org>
To:     Geert Uytterhoeven <geert+renesas@...der.be>,
        Thierry Reding <thierry.reding@...il.com>,
        Lee Jones <lee.jones@...aro.org>,
        Jingoo Han <jingoohan1@...il.com>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>
Cc:     Peter Ujfalusi <peter.ujfalusi@...com>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        linux-pwm@...r.kernel.org, linux-fbdev@...r.kernel.org,
        linux-renesas-soc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] backlight: pwm_bl: Fix GPIO out for unimplemented
 .get_direction()

On 24/03/17 16:42, Daniel Thompson wrote:
> On 22/03/17 17:21, Geert Uytterhoeven wrote:
>> Commit 7613c922315e308a ("backlight: pwm_bl: Move the checks for initial
>> power state to a separate function") not just moved some code, but made
>> slight changes in semantics.
>>
>> If a gpiochip doesn't implement the optional .get_direction() callback,
>> gpiod_get_direction always returns -EINVAL, which is never equal to
>> GPIOF_DIR_IN, leading to the GPIO not being configured for output.
>>
>> To avoid this, invert the test and check for not GPIOF_DIR_OUT instead,
>> like the original code did.
>>
>> This restores the display on r8a7740/armadillo.
>>
>> Fixes: 7613c922315e308a ("backlight: pwm_bl: Move the checks for
>> initial power state to a separate function")
>> Signed-off-by: Geert Uytterhoeven <geert+renesas@...der.be>
>
> Acked-by: Daniel Thommpson <daniel.thompson@...aro.org>

Actually, it would be better if there only one m...

Acked-by: Daniel Thompson <daniel.thompson@...aro.org>


Daniel.

>
>
>> ---
>>  drivers/video/backlight/pwm_bl.c | 7 ++++---
>>  1 file changed, 4 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/video/backlight/pwm_bl.c
>> b/drivers/video/backlight/pwm_bl.c
>> index d7efcb632f7d9dde..002f1ce22bd02032 100644
>> --- a/drivers/video/backlight/pwm_bl.c
>> +++ b/drivers/video/backlight/pwm_bl.c
>> @@ -297,14 +297,15 @@ static int pwm_backlight_probe(struct
>> platform_device *pdev)
>>      }
>>
>>      /*
>> -     * If the GPIO is configured as input, change the direction to
>> output
>> -     * and set the GPIO as active.
>> +     * If the GPIO is not known to be already configured as output, that
>> +     * is, if gpiod_get_direction returns either GPIOF_DIR_IN or
>> -EINVAL,
>> +     * change the direction to output and set the GPIO as active.
>>       * Do not force the GPIO to active when it was already output as it
>>       * could cause backlight flickering or we would enable the
>> backlight too
>>       * early. Leave the decision of the initial backlight state for
>> later.
>>       */
>>      if (pb->enable_gpio &&
>> -        gpiod_get_direction(pb->enable_gpio) == GPIOF_DIR_IN)
>> +        gpiod_get_direction(pb->enable_gpio) != GPIOF_DIR_OUT)
>>          gpiod_direction_output(pb->enable_gpio, 1);
>>
>>      pb->power_supply = devm_regulator_get(&pdev->dev, "power");
>>
>