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

Lee, Shawn C
2019-06-25T14:51:41Z

On Tue, 25 Jun 2019, Jani Nikula <jani.nikula@intel.com> wrote:
>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.
>

What you say is correct. According to spec, write EDP_BACKLIGHT_BRIGHTNESS does not affect
if BACKLIGHT_ENABLE already be off.

Backlight enable always turn off before stop PWM output when used general eDP backlight (from SOC) control.
But AUX backlight control is a little different. I will update this patch and remove "Set PWM to 0".

>>
>> 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