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

[Jani Nikula]

On Thu, 02 Feb 2023, Stanislav Lisovskiy <stanislav.lisovskiy at intel.com> 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)
>
> v5: - Use symbol clock (32 bit per lane for DP2) instead of port
>       clock in the formula(Ville Syrjälä)
>
> Signed-off-by: Stanislav Lisovskiy <stanislav.lisovskiy at intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_dp_mst.c | 15 ++++++++++++++-
>  1 file changed, 14 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..e63132557690 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp_mst.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp_mst.c
> @@ -47,8 +47,21 @@
>  
>  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)

Stick to crtc_state naming.

>  {
> +	if (intel_dp_is_uhbr(pipe_config)) {
> +		int output_bpp = bpp;
> +		/* DisplayPort 2 128b/132b, bits per lane is always 32 */
> +		int symbol_clock = pipe_config->port_clock / 32;
> +
> +		if (output_bpp * adjusted_mode->crtc_clock >=
> +		    symbol_clock * 72) {
> +			drm_dbg_kms(&i915->drm, "UHBR check failed(required bw %d available %d)\n",
> +				    output_bpp * adjusted_mode->crtc_clock, symbol_clock * 72);
> +			return -EINVAL;
> +		}
> +	}
> +
>  	return 0;
>  }

-- 
Jani Nikula, Intel Open Source Graphics Center