Hi Philip,
On Wed, Mar 22, 2017 at 11:46 AM, Philipp Zabel <p.zabel@xxxxxxxxxxxxxx> wrote:
> On Tue, 2017-03-21 at 19:48 +0100, Geert Uytterhoeven wrote:
>> On Tue, Nov 22, 2016 at 2:41 PM, Peter Ujfalusi <peter.ujfalusi@xxxxxx> wrote:
>> > Move the checks to select the initial state for the backlight to a new
>> > function and document the checks we are doing.
>>
>> This is far from a simple "move"...
>>
>> > With the separate function it is going to be easier to fix or improve the
>> > initial power state configuration later and it is easier to read the code.
>> >
>> > Signed-off-by: Peter Ujfalusi <peter.ujfalusi@xxxxxx>
>> > Reviewed-by: Philipp Zabel <p.zabel@xxxxxxxxxxxxxx>
>> > Reviewed-by: Thierry Reding <treding@xxxxxxxxxx>
>>
>> This patch (commit 7613c922315e308a in v4.11-rc1) broke the display on
>> r8a7740/armadillo.
>>
>> > @@ -267,20 +292,16 @@ static int pwm_backlight_probe(struct platform_device *pdev)
>> > pb->enable_gpio = gpio_to_desc(data->enable_gpio);
>> > }
>> >
>> > - if (pb->enable_gpio) {
>> > - /*
>> > - * If the driver is probed from the device tree and there is a
>> > - * phandle link pointing to the backlight node, it is safe to
>> > - * assume that another driver will enable the backlight at the
>> > - * appropriate time. Therefore, if it is disabled, keep it so.
>> > - */
>> > - if (node && node->phandle &&
>> > - gpiod_get_direction(pb->enable_gpio) == GPIOF_DIR_OUT &&
>> > - gpiod_get_value(pb->enable_gpio) == 0)
>> > - initial_blank = FB_BLANK_POWERDOWN;
>> > - else
>> > - gpiod_direction_output(pb->enable_gpio, 1);
>>
>> In my case, "node" points to the "/backlight" node, but phandle is NULL.
>> Hence before, gpiod_direction_output() was called to enable the GPIO...
>>
>> > - }
>> > + /*
>> > + * If the GPIO is configured as input, 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_direction_output(pb->enable_gpio, 1);
>>
>> ... while now it's no longer called, as gpiod_get_direction() returns
>> -EINVAL.
>>
>> Indeed, r8a7740_pfc does not implement the .get_direction() callback,
>> so gpiod_get_direction() always returns -EINVAL, which is never equal
>> to GPIOF_DIR_IN.
>
> Oh, I didn't think about this at all, anymore. Though I believe to
> remember that this was the reason that I checked for
> (gpiod_get_direction(pb->enable_gpio) == GPIOF_DIR_OUT) before, so ...
>
>> Restoring the old behavior by changing the above test to
>>
>> if (pb->enable_gpio &&
>> (!node || !node->phandle ||
>> gpiod_get_direction(pb->enable_gpio) == GPIOF_DIR_IN))
>>
>> fixes the display for me, but leads to a more complex expression.
>>
>> However, changing the test to
>>
>> if (pb->enable_gpio &&
>> gpiod_get_direction(pb->enable_gpio) != GPIOF_DIR_OUT)
>>
>> also fixes the display, as an error is always different from GPIOF_DIR_OUT.
>>
>> Anyone with comments or suggestions to fix this for real?
>
> ... I'm in favor of the latter, as this is closer to the initial
> intention. I'd also mention this in the comment:
>
> /*
> * 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.
> */
Thanks, I'll cook up a patch.
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
