Re: [Intel-gfx] [PATCH 2/2] drm/i915: Implement UHBR bandwidth check

[Rodrigo Vivi <rodrigo.vivi@intel.com>]

On Mon, Jan 16, 2023 at 01:19:37PM +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)
> 
> v4: - Move UHBR check to new helper function
>     - Now both for non-DSC/DSC we use that new check as
>       one of the constraints, when figuring out output bpp
>       to be used(Ville Syrjälä)
> 
> Signed-off-by: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_dp_mst.c | 13 ++++++++++++-
>  1 file changed, 12 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_dp_mst.c b/drivers/gpu/drm/i915/display/intel_dp_mst.c
> index e3e7c305fece..b95051fed23d 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp_mst.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp_mst.c
> @@ -47,8 +47,19 @@
>  
>  static int intel_dp_mst_check_constraints(struct drm_i915_private *i915, int bpp,
>  					  const struct drm_display_mode *adjusted_mode,
> -					  struct intel_crtc_state *crtc_state)
> +					  struct intel_crtc_state *pipe_config)
>  {
> +	if (intel_dp_is_uhbr(pipe_config)) {
> +		int output_bpp = bpp;
> +
> +		if (output_bpp * adjusted_mode->crtc_clock >=
> +		    pipe_config->port_clock * 72) {
> +			drm_dbg_kms(&i915->drm, "UHBR check failed(required bw %d available %d)\n",
> +				    output_bpp * adjusted_mode->crtc_clock, pipe_config->port_clock * 72);
> +			return -EINVAL;
> +		}
> +	}
> +

the check looks correct to me, but let's wait for Ville to comment on the placement
since he was the one who first noticed the other one during commit was too late.

>  	return 0;
>  }
>  
> -- 
> 2.37.3
>