Re: [Intel-gfx] [PATCH v2 10/11] drm/i915/dp: Simplify intel_dp_max_data_rate()

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Thu, Nov 16, 2023 at 03:18:40PM +0200, Imre Deak wrote:
> Simplify intel_dp_max_data_rate() using
> drm_dp_bw_channel_coding_efficiency() to calculate the max data rate for
> both DP1.4 and UHBR link rates. This trades a redundant multiply/divide
> for readability.
> 
> Cc: Jani Nikula <jani.nikula@linux.intel.com>
> Signed-off-by: Imre Deak <imre.deak@intel.com>

Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

> ---
>  drivers/gpu/drm/i915/display/intel_dp.c | 26 ++++++++++++-------------
>  1 file changed, 12 insertions(+), 14 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
> index 209c27167e057..a93e8f6429d85 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> @@ -405,29 +405,27 @@ int intel_dp_effective_data_rate(int pixel_clock, int bpp_x16,
>  int
>  intel_dp_max_data_rate(int max_link_rate, int max_lanes)
>  {
> -	if (max_link_rate >= 1000000) {
> -		/*
> -		 * UHBR rates always use 128b/132b channel encoding, and have
> -		 * 97.71% data bandwidth efficiency. Consider max_link_rate the
> -		 * link bit rate in units of 10000 bps.
> -		 */
> -		int max_link_rate_kbps = max_link_rate * 10;
> -
> -		max_link_rate_kbps = DIV_ROUND_DOWN_ULL(mul_u32_u32(max_link_rate_kbps, 9671), 10000);
> -		max_link_rate = max_link_rate_kbps / 8;
> -	}
> +	int ch_coding_efficiency =
> +		drm_dp_bw_channel_coding_efficiency(drm_dp_is_uhbr_rate(max_link_rate));
> +	int max_link_rate_kbps = max_link_rate * 10;
>  
> +	/*
> +	 * UHBR rates always use 128b/132b channel encoding, and have
> +	 * 97.71% data bandwidth efficiency. Consider max_link_rate the
> +	 * link bit rate in units of 10000 bps.
> +	 */
>  	/*
>  	 * Lower than UHBR rates always use 8b/10b channel encoding, and have
>  	 * 80% data bandwidth efficiency for SST non-FEC. However, this turns
> -	 * out to be a nop by coincidence, and can be skipped:
> +	 * out to be a nop by coincidence:
>  	 *
>  	 *	int max_link_rate_kbps = max_link_rate * 10;
>  	 *	max_link_rate_kbps = DIV_ROUND_DOWN_ULL(max_link_rate_kbps * 8, 10);
>  	 *	max_link_rate = max_link_rate_kbps / 8;
>  	 */
> -
> -	return max_link_rate * max_lanes;
> +	return DIV_ROUND_DOWN_ULL(mul_u32_u32(max_link_rate_kbps * max_lanes,
> +					      ch_coding_efficiency),
> +				  1000000 * 8);
>  }
>  
>  bool intel_dp_can_bigjoiner(struct intel_dp *intel_dp)
> -- 
> 2.39.2

-- 
Ville Syrjälä
Intel