Re: [v4 1/4] drm/panel-simple: Add basic DPCD backlight support

[Lyude Paul <lyude@redhat.com>]

oh-looks like my patches just got reviewed, so hopefully I should get a chance
to get a look at this in the next day or two :)

On Tue, 2021-05-25 at 13:00 +0530, Rajeev Nandan wrote:
> Add basic support of panel backlight control over eDP aux channel
> using VESA's standard backlight control interface.
> 
> Signed-off-by: Rajeev Nandan <rajeevny@codeaurora.org>
> ---
> 
> This patch depends on [1] (drm/panel: panel-simple: Stash DP AUX bus; 
> allow using it for DDC) 
> 
> Changes in v4:
> - New
> 
> [1]
> https://lore.kernel.org/dri-devel/20210524165920.v8.7.I18e60221f6d048d14d6c50a770b15f356fa75092@changeid/
> 
>  drivers/gpu/drm/panel/panel-simple.c | 99
> ++++++++++++++++++++++++++++++++++--
>  1 file changed, 96 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/panel/panel-simple.c
> b/drivers/gpu/drm/panel/panel-simple.c
> index b09be6e..f9e4e60 100644
> --- a/drivers/gpu/drm/panel/panel-simple.c
> +++ b/drivers/gpu/drm/panel/panel-simple.c
> @@ -21,6 +21,7 @@
>   * DEALINGS IN THE SOFTWARE.
>   */
>  
> +#include <linux/backlight.h>
>  #include <linux/delay.h>
>  #include <linux/gpio/consumer.h>
>  #include <linux/iopoll.h>
> @@ -171,6 +172,19 @@ struct panel_desc {
>  
>         /** @connector_type: LVDS, eDP, DSI, DPI, etc. */
>         int connector_type;
> +
> +       /**
> +        * @uses_dpcd_backlight: Panel supports eDP dpcd backlight control.
> +        *
> +        * Set true, if the panel supports backlight control over eDP AUX
> channel
> +        * using DPCD registers as per VESA's standard.
> +        */
> +       bool uses_dpcd_backlight;
> +};
> +
> +struct edp_backlight {
> +       struct backlight_device *dev;
> +       struct drm_edp_backlight_info info;
>  };
>  
>  struct panel_simple {
> @@ -194,6 +208,8 @@ struct panel_simple {
>  
>         struct edid *edid;
>  
> +       struct edp_backlight *edp_bl;
> +
>         struct drm_display_mode override_mode;
>  
>         enum drm_panel_orientation orientation;
> @@ -330,10 +346,14 @@ static void panel_simple_wait(ktime_t start_ktime,
> unsigned int min_ms)
>  static int panel_simple_disable(struct drm_panel *panel)
>  {
>         struct panel_simple *p = to_panel_simple(panel);
> +       struct edp_backlight *bl = p->edp_bl;
>  
>         if (!p->enabled)
>                 return 0;
>  
> +       if (p->desc->uses_dpcd_backlight && bl)
> +               drm_edp_backlight_disable(p->aux, &bl->info);
> +
>         if (p->desc->delay.disable)
>                 msleep(p->desc->delay.disable);
>  
> @@ -496,6 +516,7 @@ static int panel_simple_prepare(struct drm_panel *panel)
>  static int panel_simple_enable(struct drm_panel *panel)
>  {
>         struct panel_simple *p = to_panel_simple(panel);
> +       struct edp_backlight *bl = p->edp_bl;
>  
>         if (p->enabled)
>                 return 0;
> @@ -505,6 +526,10 @@ static int panel_simple_enable(struct drm_panel *panel)
>  
>         panel_simple_wait(p->prepared_time, p->desc-
> >delay.prepare_to_enable);
>  
> +       if (p->desc->uses_dpcd_backlight && bl)
> +               drm_edp_backlight_enable(p->aux, &bl->info,
> +                                        bl->dev->props.brightness);
> +
>         p->enabled = true;
>  
>         return 0;
> @@ -565,6 +590,59 @@ static const struct drm_panel_funcs panel_simple_funcs
> = {
>         .get_timings = panel_simple_get_timings,
>  };
>  
> +static int edp_backlight_update_status(struct backlight_device *bd)
> +{
> +       struct panel_simple *p = bl_get_data(bd);
> +       struct edp_backlight *bl = p->edp_bl;
> +
> +       if (!p->enabled)
> +               return 0;
> +
> +       return drm_edp_backlight_set_level(p->aux, &bl->info, bd-
> >props.brightness);
> +}
> +
> +static const struct backlight_ops edp_backlight_ops = {
> +       .update_status = edp_backlight_update_status,
> +};
> +
> +static int edp_backlight_register(struct device *dev, struct panel_simple
> *panel)
> +{
> +       struct edp_backlight *bl;
> +       struct backlight_properties props = { 0 };
> +       u16 current_level;
> +       u8 current_mode;
> +       u8 edp_dpcd[EDP_DISPLAY_CTL_CAP_SIZE];
> +       int ret;
> +
> +       bl = devm_kzalloc(dev, sizeof(*bl), GFP_KERNEL);
> +       if (!bl)
> +               return -ENOMEM;
> +
> +       ret = drm_dp_dpcd_read(panel->aux, DP_EDP_DPCD_REV, edp_dpcd,
> +                              EDP_DISPLAY_CTL_CAP_SIZE);
> +       if (ret < 0)
> +               return ret;
> +
> +       ret = drm_edp_backlight_init(panel->aux, &bl->info, 0, edp_dpcd,
> +                                    &current_level, &current_mode);
> +       if (ret < 0)
> +               return ret;
> +
> +       props.type = BACKLIGHT_RAW;
> +       props.brightness = current_level;
> +       props.max_brightness = bl->info.max;
> +
> +       bl->dev = devm_backlight_device_register(dev, "edp_backlight",
> +                                               dev, panel,
> +                                               &edp_backlight_ops, &props);
> +       if (IS_ERR(bl->dev))
> +               return PTR_ERR(bl->dev);
> +
> +       panel->edp_bl = bl;
> +
> +       return 0;
> +}
> +
>  static struct panel_desc panel_dpi;
>  
>  static int panel_dpi_probe(struct device *dev,
> @@ -796,9 +874,24 @@ static int panel_simple_probe(struct device *dev, const
> struct panel_desc *desc,
>  
>         drm_panel_init(&panel->base, dev, &panel_simple_funcs,
> connector_type);
>  
> -       err = drm_panel_of_backlight(&panel->base);
> -       if (err)
> -               goto disable_pm_runtime;
> +       if (panel->desc->uses_dpcd_backlight) {
> +               if (!panel->aux) {
> +                       dev_err(dev, "edp backlight needs DP aux\n");
> +                       err = -EINVAL;
> +                       goto disable_pm_runtime;
> +               }
> +
> +               err = edp_backlight_register(dev, panel);
> +               if (err) {
> +                       dev_err(dev, "failed to register edp backlight
> %d\n", err);
> +                       goto disable_pm_runtime;
> +               }
> +
> +       } else {
> +               err = drm_panel_of_backlight(&panel->base);
> +               if (err)
> +                       goto disable_pm_runtime;
> +       }
>  
>         drm_panel_add(&panel->base);
>  

-- 
Cheers,
 Lyude Paul (she/her)
 Software Engineer at Red Hat