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SubjectRe: [PATCH v2 2/4] pwm-backlight: add support for pwm-delay-us property
On Thu 2017-07-06 10:01:32, Thierry Reding wrote:
> On Fri, Jun 30, 2017 at 01:21:07PM +0200, Enric Balletbo i Serra wrote:
> > From: huang lin <hl@rock-chips.com>
> >
> > Some panels (i.e. N116BGE-L41), in their power sequence specifications,
> > request a delay between set the PWM signal and enable the backlight and
> > between clear the PWM signal and disable the backlight. Add support for
> > the new pwm-delay-us property to meet the timing.
> >
> > Note that this patch inverts current sequence. Before this patch the
> > enable signal was set before the PWM signal and vice-versa on power off.
> >
> > I assumed that this sequence was wrong, at least it is on different panel
> > datasheets that I checked, so I inverted the sequence to follow:
> >
> > On power on, set the PWM signal, wait, and set the LED_EN signal.
> > On power off, clear the LED_EN signal, wait, and stop the PWM signal.
>
> I think this should be two separate patches to make it easier to revert
> the inverted sequence should it prove to regress on other panels.

Don't make this overly complex. This is trivial. No need to split it
into more patches.


> Two more comments below.
>
> > Signed-off-by: huang lin <hl@rock-chips.com>
> > Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>
> > ---
> > Changes since v1:
> > - As suggested by Daniel Thompson
> > - Do not assume power-on delay and power-off delay will be the same
> > - Move the check of dt property to the parse dt function.
> >
> > v1: https://lkml.org/lkml/2017/6/28/219
> >
> > drivers/video/backlight/pwm_bl.c | 24 ++++++++++++++++++++----
> > include/linux/pwm_backlight.h | 1 +
> > 2 files changed, 21 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/video/backlight/pwm_bl.c b/drivers/video/backlight/pwm_bl.c
> > index 002f1ce..0f5470e 100644
> > --- a/drivers/video/backlight/pwm_bl.c
> > +++ b/drivers/video/backlight/pwm_bl.c
> > @@ -10,6 +10,7 @@
> > * published by the Free Software Foundation.
> > */
> >
> > +#include <linux/delay.h>
> > #include <linux/gpio/consumer.h>
> > #include <linux/gpio.h>
> > #include <linux/module.h>
> > @@ -35,6 +36,7 @@ struct pwm_bl_data {
> > struct gpio_desc *enable_gpio;
> > unsigned int scale;
> > bool legacy;
> > + unsigned int pwm_delay[2];
> > int (*notify)(struct device *,
> > int brightness);
> > void (*notify_after)(struct device *,
> > @@ -54,10 +56,14 @@ static void pwm_backlight_power_on(struct pwm_bl_data *pb, int brightness)
> > if (err < 0)
> > dev_err(pb->dev, "failed to enable power supply\n");
> >
> > + pwm_enable(pb->pwm);
> > +
> > + if (pb->pwm_delay[0])
> > + usleep_range(pb->pwm_delay[0], pb->pwm_delay[0] + 2000);
>
> 2000 us is kind of arbitrary. What if pwm_delay[0] is on the order of 20
> us? Making the delay 2 ms longer (in the worst case) seems somewhat
> excessive. Why not something like:
>
> usleep_range(pb->pwm_delay[0], pb->pwm_delay[0] * 2);
>
> ?
>
> > +
> > if (pb->enable_gpio)
> > gpiod_set_value_cansleep(pb->enable_gpio, 1);
> >
> > - pwm_enable(pb->pwm);
> > pb->enabled = true;
> > }
> >
> > @@ -66,12 +72,15 @@ static void pwm_backlight_power_off(struct pwm_bl_data *pb)
> > if (!pb->enabled)
> > return;
> >
> > - pwm_config(pb->pwm, 0, pb->period);
> > - pwm_disable(pb->pwm);
> > -
> > if (pb->enable_gpio)
> > gpiod_set_value_cansleep(pb->enable_gpio, 0);
> >
> > + if (pb->pwm_delay[1])
> > + usleep_range(pb->pwm_delay[1], pb->pwm_delay[1] + 2000);
> > +
> > + pwm_config(pb->pwm, 0, pb->period);
> > + pwm_disable(pb->pwm);
> > +
> > regulator_disable(pb->power_supply);
> > pb->enabled = false;
> > }
> > @@ -174,6 +183,12 @@ static int pwm_backlight_parse_dt(struct device *dev,
> > data->max_brightness--;
> > }
> >
> > + /* read pwm to enable pre/post delays from DT property */
>
> This comment is confusing. This isn't reading anything from the PWM.
>
> Thierry



--
(english) http://www.livejournal.com/~pavelmachek
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