> -----Original Message-----
> From:
> Sent: Monday, August 23, 2021 2:34 PM
> To: Kulkarni, Vandita <vandita.kulkarni@xxxxxxxxx>; intel-
> gfx@xxxxxxxxxxxxxxxxxxxxx
> Cc: Nikula, Jani <jani.nikula@xxxxxxxxx>; ville.syrjala@xxxxxxxxxxxxxxx; Chiou,
> Cooper <cooper.chiou@xxxxxxxxx>; Tseng, William
> <william.tseng@xxxxxxxxx>; Jani Nikula <jani.nikula@xxxxxxxxxxxxxxx>
> Subject: RE: [v4 6/7] drm/i915/dsi: Retrieve max brightness level from VBT.
>
> On Mon, 23 Aug 2021, Kulkarni, Vandita <vandita.kulkarni@xxxxxxxxx> 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@xxxxxxxxxxxxxxx>
> >> Cc: Jani Nikula <jani.nikula@xxxxxxxxxxxxxxx>
> >> Cc: Vandita Kulkarni <vandita.kulkarni@xxxxxxxxx>
> >> Cc: Cooper Chiou <cooper.chiou@xxxxxxxxx>
> >> Cc: William Tseng <william.tseng@xxxxxxxxx>
> >> Signed-off-by: Lee Shawn C <shawn.c.lee@xxxxxxxxx>
> >> ---
> >> 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?
Precision bits are defined from version 236 of VBT , if that is not valid or is equal to 8 then max brightness should be 0xFF.
>
> >> +#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
