Re: [RFC 1/5] drm/i915/dp: Program source OUI on eDP panels

[Rodrigo Vivi]

On Tue, Sep 15, 2020 at 01:29:35PM -0400, Lyude Paul wrote:
> Since we're about to start adding support for Intel's magic HDR
> backlight interface over DPCD, we need to ensure we're properly
> programming this field so that Intel specific sink services are exposed.
> Otherwise, 0x300-0x3ff will just read zeroes.
> 
> We also take care not to reprogram the source OUI if it already matches
> what we expect. This is just to be careful so that we don't accidentally
> take the panel out of any backlight control modes we found it in.
> 
> Signed-off-by: Lyude Paul <lyude@xxxxxxxxxx>
> Cc: thaytan@xxxxxxxxxxxx
> Cc: Vasily Khoruzhick <anarsoul@xxxxxxxxx>
> ---
>  drivers/gpu/drm/i915/display/intel_dp.c | 32 +++++++++++++++++++++++++
>  1 file changed, 32 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
> index 4bd10456ad188..b591672ec4eab 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> @@ -3428,6 +3428,7 @@ void intel_dp_sink_set_decompression_state(struct intel_dp *intel_dp,
>  void intel_dp_sink_dpms(struct intel_dp *intel_dp, int mode)
>  {
>  	struct drm_i915_private *i915 = dp_to_i915(intel_dp);
> +	u8 edp_oui[] = { 0x00, 0xaa, 0x01 };

what are these values?

>  	int ret, i;
>  
>  	/* Should have a valid DPCD by this point */
> @@ -3443,6 +3444,14 @@ void intel_dp_sink_dpms(struct intel_dp *intel_dp, int mode)
>  	} else {
>  		struct intel_lspcon *lspcon = dp_to_lspcon(intel_dp);
>  
> +		/* Write the source OUI as early as possible */
> +		if (intel_dp_is_edp(intel_dp)) {
> +			ret = drm_dp_dpcd_write(&intel_dp->aux, DP_SOURCE_OUI, edp_oui,
> +						sizeof(edp_oui));
> +			if (ret < 0)
> +				drm_err(&i915->drm, "Failed to write eDP source OUI\n");
> +		}
> +
>  		/*
>  		 * When turning on, we need to retry for 1ms to give the sink
>  		 * time to wake up.
> @@ -4530,6 +4539,23 @@ static void intel_dp_get_dsc_sink_cap(struct intel_dp *intel_dp)
>  	}
>  }
>  
> +static void
> +intel_edp_init_source_oui(struct intel_dp *intel_dp)
> +{
> +	struct drm_i915_private *i915 = dp_to_i915(intel_dp);
> +	u8 oui[] = { 0x00, 0xaa, 0x01 };
> +	u8 buf[3] = { 0 };
> +
> +	if (drm_dp_dpcd_read(&intel_dp->aux, DP_SOURCE_OUI, buf, sizeof(buf)) < 0)
> +		drm_err(&i915->drm, "Failed to read source OUI\n");
> +
> +	if (memcmp(oui, buf, sizeof(oui)) == 0)
> +		return;
> +
> +	if (drm_dp_dpcd_write(&intel_dp->aux, DP_SOURCE_OUI, oui, sizeof(oui)) < 0)
> +		drm_err(&i915->drm, "Failed to write source OUI\n");
> +}
> +
>  static bool
>  intel_edp_init_dpcd(struct intel_dp *intel_dp)
>  {
> @@ -4607,6 +4633,12 @@ intel_edp_init_dpcd(struct intel_dp *intel_dp)
>  	if (INTEL_GEN(dev_priv) >= 10 || IS_GEMINILAKE(dev_priv))
>  		intel_dp_get_dsc_sink_cap(intel_dp);
>  
> +	/*
> +	 * Program our source OUI so we can make various Intel-specific AUX
> +	 * services available (such as HDR backlight controls)
> +	 */
> +	intel_edp_init_source_oui(intel_dp);

I believe we should restrict this to the supported platforms: cfl, whl, cml, icl, tgl
no?

> +
>  	return true;
>  }
>  
> -- 
> 2.26.2
> 
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