Re: [PATCH v7 3/9] drm/i915: Drop AUX backlight enable check for backlight control

["Pandiyan, Dhinakaran" <dhinakaran.pandiyan@intel.com>]

On Thu, 2017-05-11 at 16:02 -0700, Puthikorn Voravootivat wrote:
> There are some panel that
> (1) does not support display backlight enable via AUX
> (2) support display backlight adjustment via AUX
> (3) support display backlight enable via eDP BL_ENABLE pin
> 
> The current driver required that (1) must be support to enable (2).
> This patch drops that requirement.
> 

You sent this version before I finished my follow-up questions, copying
the conversation here for context. 


DK: Won't DP_EDP_BACKLIGHT_AUX_ENABLE_CAP be 1 always? The code below,
in
intel_dp_aux_display_control_capable(), makes sure
DP_EDP_BACKLIGHT_PIN_ENABLE_CAP=0. The spec says at least one of these
has to be 1.

Puthikorn: We will drop the  DP_EDP_BACKLIGHT_PIN_ENABLE_CAP != 0 check
in next patch set.
This patch adds check here to prepare for that.


1) So, this patch does not really fix what the commit message claims
because it is dependent on the following patch. Does it make sense to
remove this check in this patch? That way, this patch by itself is the
fix that the commit message says.

-           !((intel_dp->edp_dpcd[1] & DP_EDP_BACKLIGHT_PIN_ENABLE_CAP) 


2) If a panel supports backlight enable via AUX and BL_ENABLE pin, this
patch (along with the next) enables backlight twice, doesn't it?
_intel_edp_backlight_on(intel_dp) in intel_dp.c is called
unconditionally after intel_dp_aux_enable_backlight(). I don't know how
likely this configuration is or if it's alright to enable via both AUX
and BL_ENABLE pin.




> Signed-off-by: Puthikorn Voravootivat <puthik@chromium.org>
> ---
>  drivers/gpu/drm/i915/intel_dp_aux_backlight.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_dp_aux_backlight.c b/drivers/gpu/drm/i915/intel_dp_aux_backlight.c
> index 870c03fc0f3a..c22712762957 100644
> --- a/drivers/gpu/drm/i915/intel_dp_aux_backlight.c
> +++ b/drivers/gpu/drm/i915/intel_dp_aux_backlight.c
> @@ -28,6 +28,10 @@ static void set_aux_backlight_enable(struct intel_dp *intel_dp, bool enable)
>  {
>  	uint8_t reg_val = 0;
>  
> +       /* Early return when display use other mechanism to enable backlight. */
> +	if (!(intel_dp->edp_dpcd[1] & DP_EDP_BACKLIGHT_AUX_ENABLE_CAP))
> +		return;
> +
>  	if (drm_dp_dpcd_readb(&intel_dp->aux, DP_EDP_DISPLAY_CONTROL_REGISTER,
>  			      &reg_val) < 0) {
>  		DRM_DEBUG_KMS("Failed to read DPCD register 0x%x\n",
> @@ -164,7 +168,6 @@ intel_dp_aux_display_control_capable(struct intel_connector *connector)
>  	 * the panel can support backlight control over the aux channel
>  	 */
>  	if (intel_dp->edp_dpcd[1] & DP_EDP_TCON_BACKLIGHT_ADJUSTMENT_CAP &&
> -	    (intel_dp->edp_dpcd[1] & DP_EDP_BACKLIGHT_AUX_ENABLE_CAP) &&
>  	    (intel_dp->edp_dpcd[2] & DP_EDP_BACKLIGHT_BRIGHTNESS_AUX_SET_CAP) &&
>  	    !((intel_dp->edp_dpcd[1] & DP_EDP_BACKLIGHT_PIN_ENABLE_CAP) ||
>  	      (intel_dp->edp_dpcd[2] & DP_EDP_BACKLIGHT_BRIGHTNESS_PWM_PIN_CAP))) {

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