Re: [PATCH] drm/i915: Refine eDP aux backlight enable/disable sequence

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

On Thu, 20 Jun 2019, Lee Shawn C <shawn.c.lee@intel.com> wrote:
> Modify aux backlight enable/disable sequence just like what we
> did for genernal eDP panel.
> 1. Setup PWM freq and brightness level before enable display backlight.
> 2. Set PWM to 0 after backlight enable was off.

It took me a while to realize why we do this in this order.

eDP v1.4b says about DPCD addresses 00722h-00723h
i.e. EDP_BACKLIGHT_BRIGHTNESS MSB and LSB:

"""
Writes are ignored if:

[...]

- BACKLIGHT_ENABLE bit in the EDP_DISPLAY_CONTROL register (DPCD Address
  00720h, bit 0) is cleared to 0"
"""

i.e. per the spec this change makes the brightness updates no-ops.

Do you have a panel where this patch makes a difference?

BR,
Jani.


>
> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> Cc: Jani Nikula <jani.nikula@intel.com>
> Cc: Jose Roberto de Souza <jose.souza@intel.com>
> Cc: Cooper Chiou <cooper.chiou@intel.com>
>
> Signed-off-by: Lee Shawn C <shawn.c.lee@intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c b/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
> index 6b0b73479fb8..bbc579734238 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
> @@ -216,13 +216,14 @@ static void intel_dp_aux_enable_backlight(const struct intel_crtc_state *crtc_st
>  		}
>  	}
>  
> -	set_aux_backlight_enable(intel_dp, true);
>  	intel_dp_aux_set_backlight(conn_state, connector->panel.backlight.level);
> +	set_aux_backlight_enable(intel_dp, true);
>  }
>  
>  static void intel_dp_aux_disable_backlight(const struct drm_connector_state *old_conn_state)
>  {
>  	set_aux_backlight_enable(enc_to_intel_dp(old_conn_state->best_encoder), false);
> +	intel_dp_aux_set_backlight(old_conn_state, 0);
>  }
>  
>  static int intel_dp_aux_setup_backlight(struct intel_connector *connector,

-- 
Jani Nikula, Intel Open Source Graphics Center
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