[Intel-gfx] [PATCH RESEND v4 2/6] drm/i915: Correctly enable blacklight adjustment via DPCD

[Jani Nikula]

On Tue, 18 Apr 2017, Puthikorn Voravootivat <puthik at chromium.org> wrote:
> intel_dp_aux_enable_backlight() assumed that the register
> BACKLIGHT_BRIGHTNESS_CONTROL_MODE can only has value 01
> (DP_EDP_BACKLIGHT_CONTROL_MODE_PRESET) when initialize.
>
> This patch fixed that by handling all cases of that register.

Fixes like this should precede the functional changes, i.e. this should
be earlier in the series.

>
> Signed-off-by: Puthikorn Voravootivat <puthik at chromium.org>
> ---
>  drivers/gpu/drm/i915/intel_dp_aux_backlight.c | 29 +++++++++++++++++++++------
>  1 file changed, 23 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_dp_aux_backlight.c b/drivers/gpu/drm/i915/intel_dp_aux_backlight.c
> index 42f73d9a3ccf..f06c8381c74e 100644
> --- a/drivers/gpu/drm/i915/intel_dp_aux_backlight.c
> +++ b/drivers/gpu/drm/i915/intel_dp_aux_backlight.c
> @@ -101,15 +101,32 @@ static void intel_dp_aux_enable_backlight(struct intel_connector *connector)
>  {
>  	struct intel_dp *intel_dp = enc_to_intel_dp(&connector->encoder->base);
>  	uint8_t dpcd_buf = 0;
> +	uint8_t edp_backlight_mode = 0;
>  
>  	set_aux_backlight_enable(intel_dp, true);
>  
> -	if ((drm_dp_dpcd_readb(&intel_dp->aux,
> -			       DP_EDP_BACKLIGHT_MODE_SET_REGISTER, &dpcd_buf) == 1) &&
> -	    ((dpcd_buf & DP_EDP_BACKLIGHT_CONTROL_MODE_MASK) ==
> -	     DP_EDP_BACKLIGHT_CONTROL_MODE_PRESET))
> -		drm_dp_dpcd_writeb(&intel_dp->aux, DP_EDP_BACKLIGHT_MODE_SET_REGISTER,
> -				   (dpcd_buf | DP_EDP_BACKLIGHT_CONTROL_MODE_DPCD));

Ugh, that's really totally busted, since this actually enables the
product mode because it doesn't mask out the preset first. Thanks for
fixing this.

> +	if (!drm_dp_dpcd_readb(&intel_dp->aux,
> +			       DP_EDP_BACKLIGHT_MODE_SET_REGISTER, &dpcd_buf)) {

I don't think there are any valid scenarious where this call would
return 0. if (... != 1) is the right check.

> +		return;
> +	}
> +
> +	edp_backlight_mode = dpcd_buf & DP_EDP_BACKLIGHT_CONTROL_MODE_MASK;
> +
> +	switch (edp_backlight_mode) {
> +	case DP_EDP_BACKLIGHT_CONTROL_MODE_PWM:
> +	case DP_EDP_BACKLIGHT_CONTROL_MODE_PRESET:
> +	case DP_EDP_BACKLIGHT_CONTROL_MODE_PRODUCT:
> +		dpcd_buf &= ~DP_EDP_BACKLIGHT_CONTROL_MODE_MASK;
> +		dpcd_buf |= DP_EDP_BACKLIGHT_CONTROL_MODE_DPCD;
> +		drm_dp_dpcd_writeb(&intel_dp->aux,
> +			DP_EDP_BACKLIGHT_MODE_SET_REGISTER, dpcd_buf);

I wonder if the right order would be to set the mode first, and call
set_aux_backlight_enable() after that. I couldn't find anything about
that in the spec, but gut feeling says that would be better. Needs to be
a separate change though.

BR,
Jani.

> +		break;
> +
> +	/* Do nothing when it is already DPCD mode */
> +	case DP_EDP_BACKLIGHT_CONTROL_MODE_DPCD:
> +	default:
> +		break;
> +	}
>  }
>  
>  static void intel_dp_aux_disable_backlight(struct intel_connector *connector)

-- 
Jani Nikula, Intel Open Source Technology Center