drm/i915: Replace to_bpp_frac() with fxp_q4_to_frac()

Replace the to_bpp_frac() helper defined by the driver with the
equivalent fxp_q4_to_frac() helper defined by DRM core.

v2: Rebase on the s/drm_x16/fxp_q4 change.
Acked-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240805150802.3568970-5-imre.deak@intel.com

drivers/gpu/drm/i915/display/intel_display_types.h

@@ -2200,13 +2200,8 @@ to_intel_frontbuffer(struct drm_framebuffer *fb)
 	return fb ? to_intel_framebuffer(fb)->frontbuffer : NULL;
 }
 
-static inline int to_bpp_frac(int bpp_x16)
-{
-	return bpp_x16 & 0xf;
-}
-
 #define BPP_X16_FMT		"%d.%04d"
-#define BPP_X16_ARGS(bpp_x16)	fxp_q4_to_int(bpp_x16), (to_bpp_frac(bpp_x16) * 625)
+#define BPP_X16_ARGS(bpp_x16)	fxp_q4_to_int(bpp_x16), (fxp_q4_to_frac(bpp_x16) * 625)
 
 /*
  * Conversion functions/macros from various pointer types to struct

drivers/gpu/drm/i915/display/intel_dp.c

@@ -2066,7 +2066,7 @@ xelpd_dsc_compute_link_config(struct intel_dp *intel_dp,
 	     compressed_bppx16 >= dsc_min_bpp;
 	     compressed_bppx16 -= bppx16_step) {
 		if (intel_dp->force_dsc_fractional_bpp_en &&
-		    !to_bpp_frac(compressed_bppx16))
+		    !fxp_q4_to_frac(compressed_bppx16))
 			continue;
 		ret = dsc_compute_link_config(intel_dp,
 					      pipe_config,
@@ -2076,7 +2076,7 @@ xelpd_dsc_compute_link_config(struct intel_dp *intel_dp,
 		if (ret == 0) {
 			pipe_config->dsc.compressed_bpp_x16 = compressed_bppx16;
 			if (intel_dp->force_dsc_fractional_bpp_en &&
-			    to_bpp_frac(compressed_bppx16))
+			    fxp_q4_to_frac(compressed_bppx16))
 				drm_dbg_kms(&i915->drm, "Forcing DSC fractional bpp\n");
 
 			return 0;

drivers/gpu/drm/i915/display/intel_vdsc.c

@@ -185,7 +185,7 @@ calculate_rc_params(struct drm_dsc_config *vdsc_cfg)
 		}
 	} else {
 		/* fractional bpp part * 10000 (for precision up to 4 decimal places) */
-		int fractional_bits = to_bpp_frac(vdsc_cfg->bits_per_pixel);
+		int fractional_bits = fxp_q4_to_frac(vdsc_cfg->bits_per_pixel);
 
 		static const s8 ofs_und6[] = {
 			0, -2, -2, -4, -6, -6, -8, -8, -8, -10, -10, -12, -12, -12, -12