[PATCH 02/14] drm/i915/dp: Add intel_dp_dsc_bpp_step_x16() helper to get DSC BPP precision

[Imre Deak]

On Fri, Jan 31, 2025 at 02:49:55PM +0200, Jani Nikula wrote:
> Add a platform independent helper for getting the supported DSC BPP step
> for the link.
> 
> Signed-off-by: Jani Nikula <jani.nikula at intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_dp.c | 21 ++++++++++++++++-----
>  1 file changed, 16 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
> index ecf192262eb9..a7a5bb2075da 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> @@ -2054,6 +2054,21 @@ static int dsc_src_max_compressed_bpp(struct intel_dp *intel_dp)
>  		return 27;
>  }
>  
> +/*
> + * Note: for pre-13 display you still need to check the validity of each step.
> + */
> +static int intel_dp_dsc_bpp_step_x16(const struct intel_connector *connector)

Nit: there was a guideline that these KMS objects should be passed around via
non-const pointers vs. state pointers which should be const if possible.

> +{
> +	struct intel_display *display = to_intel_display(connector);
> +	u8 incr = drm_dp_dsc_sink_bpp_incr(connector->dp.dsc_dpcd);
> +
> +	if (DISPLAY_VER(display) < 14 || !incr)
> +		return fxp_q4_from_int(1);
> +
> +	/* fxp q4 */
> +	return 16 / incr;

Nit: could've been fxp_q4_from_int(1) / incr;

Regardless of the nits, patch looks ok:

Reviewed-by: Imre Deak <imre.deak at intel.com>

> +}
> +
>  /*
>   * From a list of valid compressed bpps try different compressed bpp and find a
>   * suitable link configuration that can support it.
> @@ -2110,16 +2125,12 @@ xelpd_dsc_compute_link_config(struct intel_dp *intel_dp,
>  			      int timeslots)
>  {
>  	struct intel_display *display = to_intel_display(intel_dp);
> -	u8 bppx16_incr = drm_dp_dsc_sink_bpp_incr(connector->dp.dsc_dpcd);
>  	int output_bpp = intel_dp_output_bpp(pipe_config->output_format, pipe_bpp);
>  	u16 compressed_bppx16;
>  	u8 bppx16_step;
>  	int ret;
>  
> -	if (DISPLAY_VER(display) < 14 || bppx16_incr <= 1)
> -		bppx16_step = 16;
> -	else
> -		bppx16_step = 16 / bppx16_incr;
> +	bppx16_step = intel_dp_dsc_bpp_step_x16(connector);
>  
>  	/* Compressed BPP should be less than the Input DSC bpp */
>  	dsc_max_bpp = min(dsc_max_bpp << 4, (output_bpp << 4) - bppx16_step);
> -- 
> 2.39.5
>