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

["Lee, Shawn C" <shawn.c.lee@intel.com>]

On Tue, 24 Aug 2021, Jani Nikula <jani.nikula@linux.intel.com> wrote:
>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.
>

On vbt structure version 234 and later, vbt support brightness_precision_bits for MIPI display.
And its value will be 8~16 that defined in bpsec #20149.

If vbt version before 234 without this parameter, vbt.backlight.brightness_precision_bits will be "0".
Driver don't know panel required 8 bits or more bits for brightness control. So assign PANEL_PWM_MAX_VALUE
(0xFF) to backlight.max. And driver assign the same value when precision_bits is "8" (support max level 255). 

Best regards,
Shawn

>
>>  
>>  	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
>