From: Geert Uytterhoeven <geert@linux-m68k.org>
To: Peter Ujfalusi <peter.ujfalusi@ti.com>, Lee Jones <lee.jones@linaro.org>
Cc: Thierry Reding <thierry.reding@gmail.com>,
Tomi Valkeinen <tomi.valkeinen@ti.com>,
Linux PWM List <linux-pwm@vger.kernel.org>,
Linux Fbdev development list <linux-fbdev@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Philipp Zabel <p.zabel@pengutronix.de>,
Linus Walleij <linus.walleij@linaro.org>,
"linux-gpio@vger.kernel.org" <linux-gpio@vger.kernel.org>,
Linux-Renesas <linux-renesas-soc@vger.kernel.org>
Subject: Re: [PATCH v4 1/2] backlight: pwm_bl: Move the checks for initial power state to a separate function
Date: Tue, 21 Mar 2017 19:48:49 +0100 [thread overview]
Message-ID: <CAMuHMdXcgWyKqhZFX49Ri1eEgi1_8b_xj6P9vKwEBwpsxMXTuA@mail.gmail.com> (raw)
In-Reply-To: <20161122134123.1209-2-peter.ujfalusi@ti.com>
Hi Peter,
On Tue, Nov 22, 2016 at 2:41 PM, Peter Ujfalusi <peter.ujfalusi@ti.com> 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@ti.com>
> Reviewed-by: Philipp Zabel <p.zabel@pengutronix.de>
> Reviewed-by: Thierry Reding <treding@nvidia.com>
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.
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?
Thanks!
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org
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
next prev parent reply other threads:[~2017-03-21 18:58 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-11-22 13:41 [PATCH v4 0/2] backlight: pwm_bl: Fix the initial power state selection Peter Ujfalusi
2016-11-22 13:41 ` [PATCH v4 1/2] backlight: pwm_bl: Move the checks for initial power state to a separate function Peter Ujfalusi
2016-12-09 9:13 ` Lee Jones
2017-03-21 18:48 ` Geert Uytterhoeven [this message]
2017-03-22 10:46 ` Philipp Zabel
2017-03-22 12:30 ` Geert Uytterhoeven
2016-11-22 13:41 ` [PATCH v4 2/2] backlight: pwm_bl: Check the PWM state for initial backlight power state Peter Ujfalusi
2016-12-09 9:14 ` Lee Jones
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