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

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

On Mon, 23 Aug 2021, Kulkarni, Vandita <vandita.kulkarni@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.
>> 
>> 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_VALUE0xFF
>
>Shouldn't this be panel dependant too?

If driver did not retrieve proper precision bits, we will use PANEL_PWM_MAX_VALUE as default max backlight.
Do you recommend to keep 0xFF here?

>> +#define PANEL_PWM_MAX_VALUE0xFFFF
>> 
>>  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; backlight.level = 
>> -panel->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.

I will modify this variable name to "brightness_precision_bits". And move the max brightness calculation
into dcs_setup_backlight().

Best regards,
Shawn

>> +u16 max_brightness_level;
>>  bool present;
>>  bool active_low_pwm;
>>  u8 min_brightness;/* min_brightness/255 of max */
>> --
>> 2.17.1