Re: [Intel-gfx] [v4 6/7] drm/i915/dsi: Retrieve max brightness level from VBT.

["Kulkarni, Vandita" <vandita.kulkarni@intel.com>]

> -----Original Message-----
> From: Lee, Shawn C <shawn.c.lee@intel.com>
> Sent: Thursday, August 12, 2021 9:13 PM
> To: intel-gfx@lists.freedesktop.org
> Cc: Nikula, Jani <jani.nikula@intel.com>; ville.syrjala@linux.intel.com;
> Kulkarni, Vandita <vandita.kulkarni@intel.com>; Chiou, Cooper
> <cooper.chiou@intel.com>; Tseng, William <william.tseng@intel.com>; Lee,
> Shawn C <shawn.c.lee@intel.com>; Jani Nikula <jani.nikula@linux.intel.com>
> Subject: [v4 6/7] drm/i915/dsi: Retrieve max brightness level from VBT.
> 
> 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.
> 
> 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 +++
>  .../gpu/drm/i915/display/intel_dsi_dcs_backlight.c   | 12 +++++++++---
>  drivers/gpu/drm/i915/i915_drv.h                      |  1 +
>  3 files changed, 13 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_bios.c
> b/drivers/gpu/drm/i915/display/intel_bios.c
> index e86e6ed2d3bf..1affd679d1d1 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.max_brightness_level =
> +			(1 << backlight_data-
> >brightness_precision_bits[panel_type]) - 1;
>  	} 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..cd85520d36e2 100644
> --- a/drivers/gpu/drm/i915/display/intel_dsi_dcs_backlight.c
> +++ b/drivers/gpu/drm/i915/display/intel_dsi_dcs_backlight.c
> @@ -41,7 +41,7 @@
>  #define POWER_SAVE_HIGH			(3 << 0)
>  #define POWER_SAVE_OUTDOOR_MODE		(4 << 0)
> 
> -#define PANEL_PWM_MAX_VALUE		0xFF

Shouldn't this be panel dependant too?
> +#define PANEL_PWM_MAX_VALUE		0xFFFF
> 
>  static u32 dcs_get_backlight(struct intel_connector *connector, enum pipe
> unused)  { @@ -147,10 +147,16 @@ 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.max_brightness_level \
> +			       ? dev_priv->vbt.backlight.max_brightness_level \
> +			       : PANEL_PWM_MAX_VALUE;
> +	panel->backlight.level = dev_priv-
> >vbt.backlight.max_brightness_level \
> +				 ? dev_priv-
> >vbt.backlight.max_brightness_level \
> +				 : PANEL_PWM_MAX_VALUE;
> 
>  	return 0;
>  }
> diff --git a/drivers/gpu/drm/i915/i915_drv.h
> b/drivers/gpu/drm/i915/i915_drv.h index 005b1cec7007..fbb3f18e7b8e
> 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;

VBT doesn't provide max_brightness_level, instead it gives us Brightness Precision bits from version 236 onwards.
> +		u16 max_brightness_level;
>  		bool present;
>  		bool active_low_pwm;
>  		u8 min_brightness;	/* min_brightness/255 of max */
> --
> 2.17.1