Re: [Intel-gfx] [PATCH 06/17] drm/i915/dp: read sink UHBR rates

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Wed, Aug 18, 2021 at 09:10:41PM +0300, Jani Nikula wrote:
> See if sink supports DP 2.0 128b/132b channel encoding, and update sink
> rates accordingly.
> 
> FIXME: Also take LTTPR 128b/132b into account.
> 
> Reviewed-by: Manasi Navare <manasi.d.navare@intel.com>
> Signed-off-by: Jani Nikula <jani.nikula@intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_dp.c | 18 ++++++++++++++++++
>  1 file changed, 18 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
> index d273b3848785..079b5b37b85a 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> @@ -141,6 +141,24 @@ static void intel_dp_set_sink_rates(struct intel_dp *intel_dp)
>  		intel_dp->sink_rates[i] = dp_rates[i];
>  	}
>  
> +	/*
> +	 * Sink rates for 128b/132b. If set, sink should support all 8b/10b
> +	 * rates and 10 Gbps.
> +	 */
> +	if (intel_dp->dpcd[DP_MAIN_LINK_CHANNEL_CODING] & DP_CAP_ANSI_128B132B) {
> +		u8 uhbr_rates = 0;
> +
> +		drm_dp_dpcd_readb(&intel_dp->aux,
> +				  DP_128B132B_SUPPORTED_LINK_RATES, &uhbr_rates);
> +
> +		if (uhbr_rates & DP_UHBR10)
> +			intel_dp->sink_rates[i++] = 1000000;
> +		if (uhbr_rates & DP_UHBR13_5)
> +			intel_dp->sink_rates[i++] = 1350000;
> +		if (uhbr_rates & DP_UHBR20)
> +			intel_dp->sink_rates[i++] = 2000000;

OK, so the max link rate register isn't supposed to report the
new magic UHBR BW values it seems. That makes life a bit easier.

Maybe toss in a 
BUILD_BUG_ON(ARRAY_SIZE(sink_rates) >= ARRAY_SIZE(dp_rates)+3);
or something to remind people that we are dealing with a fixed size
array here?

Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

> +	}
> +
>  	intel_dp->num_sink_rates = i;
>  }
>  
> -- 
> 2.20.1

-- 
Ville Syrjälä
Intel