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

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(-)

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);
>

On 02-06-2021 03:50, Lyude Paul wrote:
> 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 :)
> 

Hi Lyude,

That's great!
I have updated v5 [1] of this series addressing Doug's review comments 
on v4 [2]. 
Please review the v5.

[1] 
https://lore.kernel.org/linux-arm-msm/1622390172-31368-1-git-send-email-rajeevny@codeaurora.org/
[2] 
https://lore.kernel.org/linux-arm-msm/CAD=FV=WzQ0Oc=e3kmNeBZUA+P1soKhBk8zt7bG1gqJ-Do-Tq_w@mail.gmail.com/


Thanks,
Rajeev

Lyude,

On Tue, Jun 1, 2021 at 3:20 PM Lyude Paul <lyude@redhat.com> wrote:
>
> 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 :)

I'm going to assume that means that you don't need extra eyes on your
backlight patches. If you do, please shout and I'll try to find some
cycles for it. I've always got more things to do than there are hours
in the day, but many folks from the DRM community have helped me out
with numerous reviews over the last year or two and I'm happy to pay
some of that back by giving reviews if it'll help move things forward.
:-)

-Doug