drm/i915/adlp+: Add DSC early pixel count scaling WA (Wa_1409098942)

Add a workaround to fix timing issues on links with DSC enabled -
presumedly related to the audio functionality.

Bspec requires enabling this workaround if audio is enabled on ADLP,
however Windows enables it whenever DSC is enabled ADLP onwards; follow
Windows.

Bspec: 50490, 55424

v2: Fix WA code comment formatting. (Ankit)
Reviewed-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240129175533.904590-5-imre.deak@intel.com

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

@@ -443,6 +443,14 @@ void intel_enable_transcoder(const struct intel_crtc_state *new_crtc_state)
 		return;
 	}
 
+	/* Wa_1409098942:adlp+ */
+	if (DISPLAY_VER(dev_priv) >= 13 &&
+	    new_crtc_state->dsc.compression_enable) {
+		val &= ~TRANSCONF_PIXEL_COUNT_SCALING_MASK;
+		val |= REG_FIELD_PREP(TRANSCONF_PIXEL_COUNT_SCALING_MASK,
+				      TRANSCONF_PIXEL_COUNT_SCALING_X4);
+	}
+
 	intel_de_write(dev_priv, TRANSCONF(cpu_transcoder),
 		       val | TRANSCONF_ENABLE);
 	intel_de_posting_read(dev_priv, TRANSCONF(cpu_transcoder));
@@ -489,6 +497,11 @@ void intel_disable_transcoder(const struct intel_crtc_state *old_crtc_state)
 	if (!IS_I830(dev_priv))
 		val &= ~TRANSCONF_ENABLE;
 
+	/* Wa_1409098942:adlp+ */
+	if (DISPLAY_VER(dev_priv) >= 13 &&
+	    old_crtc_state->dsc.compression_enable)
+		val &= ~TRANSCONF_PIXEL_COUNT_SCALING_MASK;
+
 	intel_de_write(dev_priv, TRANSCONF(cpu_transcoder), val);
 
 	if (DISPLAY_VER(dev_priv) >= 12)

drivers/gpu/drm/i915/i915_reg.h

@@ -2596,6 +2596,9 @@
 #define   TRANSCONF_DITHER_TYPE_ST1		REG_FIELD_PREP(TRANSCONF_DITHER_TYPE_MASK, 1)
 #define   TRANSCONF_DITHER_TYPE_ST2		REG_FIELD_PREP(TRANSCONF_DITHER_TYPE_MASK, 2)
 #define   TRANSCONF_DITHER_TYPE_TEMP		REG_FIELD_PREP(TRANSCONF_DITHER_TYPE_MASK, 3)
+#define   TRANSCONF_PIXEL_COUNT_SCALING_MASK	REG_GENMASK(1, 0)
+#define   TRANSCONF_PIXEL_COUNT_SCALING_X4	1
+
 #define _PIPEASTAT		0x70024
 #define   PIPE_FIFO_UNDERRUN_STATUS		(1UL << 31)
 #define   SPRITE1_FLIP_DONE_INT_EN_VLV		(1UL << 30)