[Intel-gfx] [PATCH] drm/i915: Implement UHBR bandwidth check

[Ville Syrjälä]

On Fri, Jan 13, 2023 at 03:06:28PM +0200, Stanislav Lisovskiy wrote:
> According to spec, we should check if output_bpp * pixel_rate is less
> than DDI clock * 72, if UHBR is used.
> 
> HSDES: 1406899791
> BSPEC: 49259
> 
> v2: - Removed wrong comment(Rodrigo Vivi)
>     - Added HSDES to the commit msg(Rodrigo Vivi)
>     - Moved UHBR check to the MST specific code
> 
> v3: - Changed commit subject(Rodrigo Vivi)
>     - Fixed the error message if check fails(Rodrigo Vivi)
> 
> Signed-off-by: Stanislav Lisovskiy <stanislav.lisovskiy at intel.com>
> Reviewed-by: Rodrigo Vivi <rodrigo.vivi at intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_dp_mst.c | 16 +++++++++++++---
>  1 file changed, 13 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_dp_mst.c b/drivers/gpu/drm/i915/display/intel_dp_mst.c
> index 8b0e4defa3f1..36e368995bef 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp_mst.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp_mst.c
> @@ -339,10 +339,20 @@ static int intel_dp_mst_compute_config(struct intel_encoder *encoder,
>  		ret = intel_dp_dsc_compute_config(intel_dp, pipe_config,
>  						  conn_state, &limits,
>  						  pipe_config->dp_m_n.tu, false);
> -	}
> +		if (ret < 0)
> +			return ret;
>  
> -	if (ret)
> -		return ret;
> +		if (intel_dp_is_uhbr(pipe_config)) {
> +			int output_bpp = pipe_config->dsc.compressed_bpp;
> +
> +			if (output_bpp * adjusted_mode->crtc_clock >=
> +			    pipe_config->port_clock * 72) {
> +				drm_dbg_kms(&dev_priv->drm, "UHBR check failed(required bw %d available %d)\n",
> +					    output_bpp * adjusted_mode->crtc_clock, pipe_config->port_clock * 72);
> +				return -EINVAL;

Doesn't this just mean the user can never enable this particular
mode? Would seem more sensible to account for the extra
limitation when we determine port_clock and/or compressed_bpp.

> +			}
> +		}
> +	}
>  
>  	ret = intel_dp_mst_update_slots(encoder, pipe_config, conn_state);
>  	if (ret)
> -- 
> 2.37.3

-- 
Ville Syrjälä
Intel