Re: [Intel-gfx] [PATCH] drm/i915/dsi: Retrieve max brightness level from VBT

[Jani Nikula <jani.nikula@linux.intel.com>]

On Tue, 24 Aug 2021, Lee Shawn C <shawn.c.lee@intel.com> wrote:
> So far, DCS backlight driver hardcode (0xFF) for max brightness level.
> MIPI DCS spec allow max 0xFFFF for set_display_brightness (51h) command.
> And VBT brightness precision bits can support 8 ~ 16 bits.
>
> We should set correct precision bits in VBT that meet panel's request.
> Driver can refer to this setting then configure max brightness level
> in DCS backlight driver properly.
>
> v2: modify variable name brightness_precision_bits instead of
>     max_brightness_level.
>
> Cc: Ville Syrjala <ville.syrjala@linux.intel.com>
> Cc: Jani Nikula <jani.nikula@linux.intel.com>
> Cc: Vandita Kulkarni <vandita.kulkarni@intel.com>
> Cc: Cooper Chiou <cooper.chiou@intel.com>
> Cc: William Tseng <william.tseng@intel.com>
> Signed-off-by: Lee Shawn C <shawn.c.lee@intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_bios.c              | 3 +++
>  drivers/gpu/drm/i915/display/intel_dsi_dcs_backlight.c | 8 ++++++--
>  drivers/gpu/drm/i915/i915_drv.h                        | 1 +
>  3 files changed, 10 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_bios.c b/drivers/gpu/drm/i915/display/intel_bios.c
> index e86e6ed2d3bf..ccaf0a3100f7 100644
> --- a/drivers/gpu/drm/i915/display/intel_bios.c
> +++ b/drivers/gpu/drm/i915/display/intel_bios.c
> @@ -483,6 +483,9 @@ parse_lfp_backlight(struct drm_i915_private *i915,
>  			level = 255;
>  		}
>  		i915->vbt.backlight.min_brightness = min_level;
> +
> +		i915->vbt.backlight.brightness_precision_bits =
> +			backlight_data->brightness_precision_bits[panel_type];
>  	} else {
>  		level = backlight_data->level[panel_type];
>  		i915->vbt.backlight.min_brightness = entry->min_brightness;
> diff --git a/drivers/gpu/drm/i915/display/intel_dsi_dcs_backlight.c b/drivers/gpu/drm/i915/display/intel_dsi_dcs_backlight.c
> index 584c14c4cbd0..21ab9e1acb57 100644
> --- a/drivers/gpu/drm/i915/display/intel_dsi_dcs_backlight.c
> +++ b/drivers/gpu/drm/i915/display/intel_dsi_dcs_backlight.c
> @@ -147,10 +147,14 @@ static void dcs_enable_backlight(const struct intel_crtc_state *crtc_state,
>  static int dcs_setup_backlight(struct intel_connector *connector,
>  			       enum pipe unused)
>  {
> +	struct drm_device *dev = connector->base.dev;
> +	struct drm_i915_private *dev_priv = to_i915(dev);
>  	struct intel_panel *panel = &connector->panel;
>  
> -	panel->backlight.max = PANEL_PWM_MAX_VALUE;
> -	panel->backlight.level = PANEL_PWM_MAX_VALUE;
> +	panel->backlight.max = (dev_priv->vbt.backlight.brightness_precision_bits > 8) \
> +			       ? (1 << dev_priv->vbt.backlight.brightness_precision_bits) - 1 \
> +			       : PANEL_PWM_MAX_VALUE;
> +	panel->backlight.level = panel->backlight.max;

If the precision is < 8, why would max be 0xff? Use GENMASK() perhaps?

BR,
Jani.


>  
>  	return 0;
>  }
> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> index 005b1cec7007..1b42e39a7cd4 100644
> --- a/drivers/gpu/drm/i915/i915_drv.h
> +++ b/drivers/gpu/drm/i915/i915_drv.h
> @@ -706,6 +706,7 @@ struct intel_vbt_data {
>  
>  	struct {
>  		u16 pwm_freq_hz;
> +		u16 brightness_precision_bits;
>  		bool present;
>  		bool active_low_pwm;
>  		u8 min_brightness;	/* min_brightness/255 of max */

-- 
Jani Nikula, Intel Open Source Graphics Center