[PATCH v6] drm/i915/display: Use the recomended min_hblank values

[Imre Deak]

On Mon, Jul 28, 2025 at 02:14:48PM +0530, Arun R Murthy wrote:
> Use recommended values as per wa_14021694213 to compare with the
> calculated value and choose minimum of them.
> 
> v2: corrected checkpatch warning and retain the restriction for
> min_hblank (Jani)
> v3: use calculated value to compare with recomended value and choose
> minimum of them (Imre)
> v4: As driver supported min bpc is 8, omit the condition check for
> bpc6 with ycbcr420. Added a note for the same (Imre)
> v5: Add a warn for the unexpected case of 6bpc + uhbr + ycbcr420
> v6: Reworded the comments and check fo anything < compressed bpp 8(Imre)
> 
> Bspec: 74379
> Signed-off-by: Arun R Murthy <arun.r.murthy at intel.com>
> ---
> Changes in v6:
> - EDITME: describe what is new in this series revision.
> - EDITME: use bulletpoints and terse descriptions.
> - Link to v5: https://lore.kernel.org/r/20250728-min_hblank-v5-1-54cb7ea5cd74@intel.com
> 
> Changes in v5:
> - EDITME: describe what is new in this series revision.
> - EDITME: use bulletpoints and terse descriptions.
> - Link to v4: https://lore.kernel.org/r/20250728-min_hblank-v4-1-b9d83bf03025@intel.com
> ---
>  drivers/gpu/drm/i915/display/intel_dp.c | 20 +++++++++++++++++++-
>  1 file changed, 19 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
> index 54d88f24b6893e1f8009f00dda87d8dae5dfc137..148848a919e09e185fce38a0636e2c2a25d33bc4 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> @@ -3182,7 +3182,25 @@ int intel_dp_compute_min_hblank(struct intel_crtc_state *crtc_state,
>  	 */
>  	min_hblank = min_hblank - 2;
>  
> -	min_hblank = min(10, min_hblank);
> +	/*
> +	 * min_hblank formula is undergoing a change, to avoid underrun use the
> +	 * recomended value in spec to compare with the calculated one and use the
> +	 * minimum value
> +	 */
> +	if (intel_dp_is_uhbr(crtc_state)) {
> +		/*
> +		 * Note: Bspec requires a min_hblank of 2 for YCBCR420
> +		 * with compressed bpp 6, but the minimum compressed bpp
> +		 * supported by the driver is 8.
> +		 */
> +		drm_WARN_ON(display->drm, (crtc_state->dsc.compression_enable &&
> +			 crtc_state->output_format == INTEL_OUTPUT_FORMAT_YCBCR420 &&
> +			 crtc_state->dsc.compressed_bpp_x16 < fxp_q4_from_int(8)));

The above two lines have an indent error, they should be aligned after
the opening ( of the function above.

Otherwise the patch looks ok:
Reviewed-by: Imre Deak <imre.deak at intel.com>

> +		min_hblank = min(3, min_hblank);
> +	} else {
> +		min_hblank = min(10, min_hblank);
> +	}
> +
>  	crtc_state->min_hblank = min_hblank;
>  
>  	return 0;
> 
> ---
> base-commit: eb0c2b25072b5c56e8c41d7099050bf53bebaa14
> change-id: 20250728-min_hblank-263ceb40508c
> 
> Best regards,
> -- 
> Arun R Murthy <arun.r.murthy at intel.com>
>