[PATCH v2] backlight: turn backlight on/off when necessary

[Liu Ying]

Ping...

Regards,
Liu Ying

On 01/20/2014 12:52 PM, Liu Ying wrote:
> We don't have to turn backlight on/off everytime a blanking
> or unblanking event comes because the backlight status may
> have already been what we want. Another thought is that one
> backlight device may be shared by multiple framebuffers. We
> don't hope blanking one of the framebuffers may turn the
> backlight off for all the other framebuffers, since they are
> likely being active to display something. This patch adds
> some logics to record each framebuffer's backlight usage to
> determine the backlight device use count and whether the
> backlight should be turned on or off. To be more specific,
> only one unblank operation on a certain blanked framebuffer
> may increase the backlight device's use count by one, while
> one blank operation on a certain unblanked framebuffer may
> decrease the use count by one, because the userspace is
> likely to unblank a unblanked framebuffer or blank a blanked
> framebuffer.
> 
> Signed-off-by: Liu Ying <Ying.Liu at freescale.com>
> ---
> v1 can be found at https://lkml.org/lkml/2013/5/30/139
> 
> v1->v2:
> * Make the commit message be more specific about the condition
>   in which backlight device use count can be increased/decreased.
> * Correct the setting for bd->props.fb_blank.
> 
>  drivers/video/backlight/backlight.c |   28 +++++++++++++++++++++-------
>  include/linux/backlight.h           |    6 ++++++
>  2 files changed, 27 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/video/backlight/backlight.c b/drivers/video/backlight/backlight.c
> index 5d05555..42044be 100644
> --- a/drivers/video/backlight/backlight.c
> +++ b/drivers/video/backlight/backlight.c
> @@ -34,13 +34,15 @@ static const char *const backlight_types[] = {
>                            defined(CONFIG_BACKLIGHT_CLASS_DEVICE_MODULE))
>  /* This callback gets called when something important happens inside a
>   * framebuffer driver. We're looking if that important event is blanking,
> - * and if it is, we're switching backlight power as well ...
> + * and if it is and necessary, we're switching backlight power as well ...
>   */
>  static int fb_notifier_callback(struct notifier_block *self,
>                                 unsigned long event, void *data)
>  {
>         struct backlight_device *bd;
>         struct fb_event *evdata = data;
> +       int node = evdata->info->node;
> +       int fb_blank = 0;
> 
>         /* If we aren't interested in this event, skip it immediately ... */
>         if (event != FB_EVENT_BLANK && event != FB_EVENT_CONBLANK)
> @@ -51,12 +53,24 @@ static int fb_notifier_callback(struct notifier_block *self,
>         if (bd->ops)
>                 if (!bd->ops->check_fb ||
>                     bd->ops->check_fb(bd, evdata->info)) {
> -                       bd->props.fb_blank = *(int *)evdata->data;
> -                       if (bd->props.fb_blank == FB_BLANK_UNBLANK)
> -                               bd->props.state &= ~BL_CORE_FBBLANK;
> -                       else
> -                               bd->props.state |= BL_CORE_FBBLANK;
> -                       backlight_update_status(bd);
> +                       fb_blank = *(int *)evdata->data;
> +                       if (fb_blank == FB_BLANK_UNBLANK &&
> +                           !bd->fb_bl_on[node]) {
> +                               bd->fb_bl_on[node] = true;
> +                               if (!bd->use_count++) {
> +                                       bd->props.state &= ~BL_CORE_FBBLANK;
> +                                       bd->props.fb_blank = FB_BLANK_UNBLANK;
> +                                       backlight_update_status(bd);
> +                               }
> +                       } else if (fb_blank != FB_BLANK_UNBLANK &&
> +                                  bd->fb_bl_on[node]) {
> +                               bd->fb_bl_on[node] = false;
> +                               if (!(--bd->use_count)) {
> +                                       bd->props.state |= BL_CORE_FBBLANK;
> +                                       bd->props.fb_blank = FB_BLANK_POWERDOWN;
> +                                       backlight_update_status(bd);
> +                               }
> +                       }
>                 }
>         mutex_unlock(&bd->ops_lock);
>         return 0;
> diff --git a/include/linux/backlight.h b/include/linux/backlight.h
> index 5f9cd96..7264742 100644
> --- a/include/linux/backlight.h
> +++ b/include/linux/backlight.h
> @@ -9,6 +9,7 @@
>  #define _LINUX_BACKLIGHT_H
> 
>  #include <linux/device.h>
> +#include <linux/fb.h>
>  #include <linux/mutex.h>
>  #include <linux/notifier.h>
> 
> @@ -104,6 +105,11 @@ struct backlight_device {
>         struct list_head entry;
> 
>         struct device dev;
> +
> +       /* Multiple framebuffers may share one backlight device */
> +       bool fb_bl_on[FB_MAX];
> +
> +       int use_count;
>  };
> 
>  static inline void backlight_update_status(struct backlight_device *bd)
> --
> 1.7.9.5