drm/i915/dsi: account for DSC in horizontal timings

When DSC is enabled, we need to adjust the horizontal timings to account
for the compressed (and therefore reduced) link speed.

The compressed frequency ratio simplifies down to the ratio between
compressed and non-compressed bpp.

Bspec: 49263
Suggested-by: Vandita Kulkarni <vandita.kulkarni@intel.com>
Cc: Vandita Kulkarni <vandita.kulkarni@intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Vandita Kulkarni <vandita.kulkarni@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/fecebdc2719dd0c78eaf8f4d3225bb185956d7db.1575974743.git.jani.nikula@intel.com

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

@@ -785,12 +785,12 @@ gen11_dsi_configure_transcoder(struct intel_encoder *encoder,
 
 static void
 gen11_dsi_set_transcoder_timings(struct intel_encoder *encoder,
-				 const struct intel_crtc_state *pipe_config)
+				 const struct intel_crtc_state *crtc_state)
 {
 	struct drm_i915_private *dev_priv = to_i915(encoder->base.dev);
 	struct intel_dsi *intel_dsi = enc_to_intel_dsi(&encoder->base);
 	const struct drm_display_mode *adjusted_mode =
-					&pipe_config->hw.adjusted_mode;
+		&crtc_state->hw.adjusted_mode;
 	enum port port;
 	enum transcoder dsi_trans;
 	/* horizontal timings */
@@ -798,11 +798,25 @@ gen11_dsi_set_transcoder_timings(struct intel_encoder *encoder,
 	u16 hback_porch;
 	/* vertical timings */
 	u16 vtotal, vactive, vsync_start, vsync_end, vsync_shift;
+	int mul = 1, div = 1;
+
+	/*
+	 * Adjust horizontal timings (htotal, hsync_start, hsync_end) to account
+	 * for slower link speed if DSC is enabled.
+	 *
+	 * The compression frequency ratio is the ratio between compressed and
+	 * non-compressed link speeds, and simplifies down to the ratio between
+	 * compressed and non-compressed bpp.
+	 */
+	if (crtc_state->dsc.compression_enable) {
+		mul = crtc_state->dsc.compressed_bpp;
+		div = mipi_dsi_pixel_format_to_bpp(intel_dsi->pixel_format);
+	}
 
 	hactive = adjusted_mode->crtc_hdisplay;
-	htotal = adjusted_mode->crtc_htotal;
-	hsync_start = adjusted_mode->crtc_hsync_start;
-	hsync_end = adjusted_mode->crtc_hsync_end;
+	htotal = DIV_ROUND_UP(adjusted_mode->crtc_htotal * mul, div);
+	hsync_start = DIV_ROUND_UP(adjusted_mode->crtc_hsync_start * mul, div);
+	hsync_end = DIV_ROUND_UP(adjusted_mode->crtc_hsync_end * mul, div);
 	hsync_size  = hsync_end - hsync_start;
 	hback_porch = (adjusted_mode->crtc_htotal -
 		       adjusted_mode->crtc_hsync_end);