[Intel-gfx] [PATCH] drm/i915: Implement workaround for DP2 UHBR bandwidth check

[Rodrigo Vivi]

on the subject: This is not a hw workaround. Please remove the workaround from
the subject and the wrong comment.

"The HSD given is a 'feature' rather than 'bugeco' so no workaround details are
present here."


On Mon, Jan 02, 2023 at 01:39:37PM +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.
> 
> Signed-off-by: Stanislav Lisovskiy <stanislav.lisovskiy at intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_dp.c | 11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
> index bf80f296a8fdb..13baf3cb5f934 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> @@ -1582,6 +1582,17 @@ int intel_dp_dsc_compute_config(struct intel_dp *intel_dp,
>  		drm_dbg_kms(&dev_priv->drm, "DSC: compressed bpp %d slice count %d\n",
>  			    pipe_config->dsc.compressed_bpp,
>  			    pipe_config->dsc.slice_count);
> +
> +		/* wa1406899791 */

even if it was a bugeco, the notation doesn't follow the standard.

But anyway, as I pointed out, this is not a workaround so
you probably just want a

HSDES: 1406899791
BSPEC: 49259

in your commit msg.

Also maybe a "Fixes:" tag pointing to the commit that added the sequence
but didn't added this part of the sequence?

> +		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, "DP2 UHBR check failed\n");

some probably dummy question:
do we need to add a check for the DP 2.0 above as well?
or it is unecessary/redundant?

> +				return -EINVAL;
> +			}
> +		}
>  	}
>  	/*
>  	 * VDSC engine operates at 1 Pixel per clock, so if peak pixel rate
> -- 
> 2.37.3
>