drm/i915/display/dsc: Force dsc BPP

Set DSC BPP to the value forced through
debugfs. It can go from bpc to bpp-1.

v2: Use default dsc bpp when we are just
    doing force_dsc_en, use default dsc bpp
    for invalid force_dsc_bpp values. (Jani)
Signed-off-by: Vandita Kulkarni <vandita.kulkarni@intel.com>
Reviewed-by: Swati Sharma <swati2.sharma@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210720064907.9771-4-vandita.kulkarni@intel.com

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

@@ -1274,6 +1274,23 @@ static int intel_dp_dsc_compute_config(struct intel_dp *intel_dp,
 							       pipe_config->pipe_bpp);
 		pipe_config->dsc.slice_count = dsc_dp_slice_count;
 	}
+
+	/* As of today we support DSC for only RGB */
+	if (intel_dp->force_dsc_bpp) {
+		if (intel_dp->force_dsc_bpp >= 8 &&
+		    intel_dp->force_dsc_bpp < pipe_bpp) {
+			drm_dbg_kms(&dev_priv->drm,
+				    "DSC BPP forced to %d",
+				    intel_dp->force_dsc_bpp);
+			pipe_config->dsc.compressed_bpp =
+						intel_dp->force_dsc_bpp;
+		} else {
+			drm_dbg_kms(&dev_priv->drm,
+				    "Invalid DSC BPP %d",
+				    intel_dp->force_dsc_bpp);
+		}
+	}
+
 	/*
 	 * VDSC engine operates at 1 Pixel per clock, so if peak pixel rate
 	 * is greater than the maximum Cdclock and if slice count is even