lkml.org 
[lkml]   [2017]   [Jul]   [6]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH v2 2/4] pwm-backlight: add support for pwm-delay-us property
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.

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
[unhandled content-type:application/pgp-signature]
\
 
 \ /
  Last update: 2017-07-06 10:02    [W:0.095 / U:10.912 seconds]
©2003-2017 Jasper Spaans. hosted at Digital OceanAdvertise on this site