[PATCH v2 1/3] drm/display/dp: Export fn to calculate link symbol cycles

[Imre Deak]

On Tue, Apr 15, 2025 at 01:25:07PM +0530, Arun R Murthy wrote:
> Unify the function to calculate the link symbol cycles for both dsc and
> non-dsc case and export the function so that it can be used in the
> respective platform display drivers for other calculations.
> 
> v2: unify the fn for both dsc and non-dsc case (Imre)
> 
> Signed-off-by: Arun R Murthy <arun.r.murthy at intel.com>
> ---
>  drivers/gpu/drm/display/drm_dp_helper.c | 47 ++++++++++++++++-----------------
>  include/drm/display/drm_dp_helper.h     |  3 +++
>  2 files changed, 26 insertions(+), 24 deletions(-)
> 
> diff --git a/drivers/gpu/drm/display/drm_dp_helper.c b/drivers/gpu/drm/display/drm_dp_helper.c
> index 57828f2b7b5a0582ca4a6f2a9be2d5909fe8ad24..1a5ff9ba6505f312ee41eb3bcc8b53d318411c03 100644
> --- a/drivers/gpu/drm/display/drm_dp_helper.c
> +++ b/drivers/gpu/drm/display/drm_dp_helper.c
> @@ -4393,25 +4393,30 @@ EXPORT_SYMBOL(drm_panel_dp_aux_backlight);
>  #endif
>  
>  /* See DP Standard v2.1 2.6.4.4.1.1, 2.8.4.4, 2.8.7 */
> -static int drm_dp_link_symbol_cycles(int lane_count, int pixels, int bpp_x16,
> -				     int symbol_size, bool is_mst)
> +/**
> + * drm_dp_link_symbol_cycles - calculate the link symbol count
> + * @lane_coount: DP link lane count
> + * @pixels: horizontal active pixels
> + * @bpp_x16: bits per pixel in .4 binary fixed format
> + * @symbol_size: DP symbol size
> + * @is_mst: is mst or sst
> + * @slice_count: number of slices
> + *
> + * Calculate the link symbol cycles for both dsc and non dsc case and
> + * return the count.
> + */
> +int drm_dp_link_symbol_cycles(int lane_count, int pixels, int bpp_x16,
> +			      int symbol_size, bool is_mst, int slice_count)
>  {
> -	int cycles = DIV_ROUND_UP(pixels * bpp_x16, 16 * symbol_size * lane_count);
> +	int pix = slice_count ? DIV_ROUND_UP(pixels, slice_count) : pixels;
> +	int cycles = DIV_ROUND_UP(pix * bpp_x16, 16 * symbol_size * lane_count);
>  	int align = is_mst ? 4 / lane_count : 1;
> +	int slice_data_cycles = ALIGN(cycles, align);
>  
> -	return ALIGN(cycles, align);
> -}
> -
> -static int drm_dp_link_dsc_symbol_cycles(int lane_count, int pixels, int slice_count,
> -					 int bpp_x16, int symbol_size, bool is_mst)
> -{
> -	int slice_pixels = DIV_ROUND_UP(pixels, slice_count);
> -	int slice_data_cycles = drm_dp_link_symbol_cycles(lane_count, slice_pixels,
> -							  bpp_x16, symbol_size, is_mst);
> -	int slice_eoc_cycles = is_mst ? 4 / lane_count : 1;
> -
> -	return slice_count * (slice_data_cycles + slice_eoc_cycles);
> +	return slice_count ? (slice_count * (slice_data_cycles + align)) :
> +			     slice_data_cycles;

I'd like to preserve in the code what the DSC EOC cycles are and the way
the data symbol cycles are calculated could be kept as-is. So could
you instead do the following, renaming drm_dp_link_symbol_cycles() to
drm_dp_link_data_symbol_cycles()?:

-static int drm_dp_link_dsc_symbol_cycles(int lane_count, int pixels, int slice_count,
-                                        int bpp_x16, int symbol_size, bool is_mst)
int drm_dp_link_symbol_cycles(int lane_count, int pixels, int dsc_slice_count,
+                             int bpp_x16, int symbol_size, bool is_mst)
 {
+       int slice_count = dsc_slice_count ? : 1;
        int slice_pixels = DIV_ROUND_UP(pixels, slice_count);
-       int slice_data_cycles = drm_dp_link_symbol_cycles(lane_count, slice_pixels,
-                                                         bpp_x16, symbol_size, is_mst);
-       int slice_eoc_cycles = is_mst ? 4 / lane_count : 1;
+       int slice_data_cycles = drm_dp_link_data_symbol_cycles(lane_count, slice_pixels,
+                                                              bpp_x16, symbol_size, is_mst);
+       int slice_eoc_cycles = 0;
+
+       if (dsc_slice_count)
+               slice_eoc_cycles = is_mst ? 4 / lane_count : 1;
 
        return slice_count * (slice_data_cycles + slice_eoc_cycles);
 }

>  }
> +EXPORT_SYMBOL(drm_dp_link_symbol_cycles);
>  
>  /**
>   * drm_dp_bw_overhead - Calculate the BW overhead of a DP link stream
> @@ -4486,15 +4491,9 @@ int drm_dp_bw_overhead(int lane_count, int hactive,
>  	WARN_ON((flags & DRM_DP_BW_OVERHEAD_UHBR) &&
>  		(flags & DRM_DP_BW_OVERHEAD_FEC));
>  
> -	if (flags & DRM_DP_BW_OVERHEAD_DSC)
> -		symbol_cycles = drm_dp_link_dsc_symbol_cycles(lane_count, hactive,
> -							      dsc_slice_count,
> -							      bpp_x16, symbol_size,
> -							      is_mst);
> -	else
> -		symbol_cycles = drm_dp_link_symbol_cycles(lane_count, hactive,
> -							  bpp_x16, symbol_size,
> -							  is_mst);
> +	symbol_cycles = drm_dp_link_symbol_cycles(lane_count, hactive,
> +						  bpp_x16, symbol_size,
> +						  is_mst, dsc_slice_count);
>  
>  	return DIV_ROUND_UP_ULL(mul_u32_u32(symbol_cycles * symbol_size * lane_count,
>  					    overhead * 16),
> diff --git a/include/drm/display/drm_dp_helper.h b/include/drm/display/drm_dp_helper.h
> index d9614e2c89397536f44bb7258e894628ae1dccc9..22ae37e7870f1008acfc980a9b46d8dea1fbbe10 100644
> --- a/include/drm/display/drm_dp_helper.h
> +++ b/include/drm/display/drm_dp_helper.h
> @@ -972,4 +972,7 @@ int drm_dp_max_dprx_data_rate(int max_link_rate, int max_lanes);
>  
>  ssize_t drm_dp_vsc_sdp_pack(const struct drm_dp_vsc_sdp *vsc, struct dp_sdp *sdp);
>  
> +int drm_dp_link_symbol_cycles(int lane_count, int pixels, int bpp_x16,
> +			      int symbol_size, bool is_mst, int slice_count);
> +
>  #endif /* _DRM_DP_HELPER_H_ */
> 
> -- 
> 2.25.1
>