Hi Thierry,

Many thanks for your comments, I'll send a v3.

2017-07-06 10:13 GMT+02:00 Thierry Reding [off-list ref]:

On Fri, Jun 30, 2017 at 01:21:07PM +0200, Enric Balletbo i Serra wrote:

quoted

From: huang lin <redacted>

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.

Signed-off-by: huang lin <redacted>
Signed-off-by: Enric Balletbo i Serra <redacted>
---
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);
+
      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 */
+     ret = of_property_read_u32_array(node, "pwm-delay-us", data->pwm_delay,
+                                      ARRAY_SIZE(data->pwm_delay));
+     if (ret < 0)
+             return ret;

Also I think you need to make sure you have a fallback in place in case
that this fails, otherwise the property is no longer optional.

Ignoring -EINVAL should do the trick since data->pwm_delay should be
zeroed out by the memset() earlier in this function.

Yep, you have reason. Thanks.

Thierry