drm/radeon: fix audio dto calculation on DCE3+ (v3)

Need to set the wallclock ratio and adjust the phase
and module registers appropriately.  May fix problems
with audio timing at certain display timings.

v2: properly handle clocks below 24mhz
v3: rebase r600 changes

Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
diff --git a/drivers/gpu/drm/radeon/r600_hdmi.c b/drivers/gpu/drm/radeon/r600_hdmi.c
index b9b1139..f264df5 100644
--- a/drivers/gpu/drm/radeon/r600_hdmi.c
+++ b/drivers/gpu/drm/radeon/r600_hdmi.c
@@ -226,10 +226,29 @@
 	struct radeon_encoder *radeon_encoder = to_radeon_encoder(encoder);
 	struct radeon_encoder_atom_dig *dig = radeon_encoder->enc_priv;
 	u32 base_rate = 24000;
+	u32 max_ratio = clock / base_rate;
+	u32 dto_phase;
+	u32 dto_modulo = clock;
+	u32 wallclock_ratio;
+	u32 dto_cntl;
 
 	if (!dig || !dig->afmt)
 		return;
 
+	if (max_ratio >= 8) {
+		dto_phase = 192 * 1000;
+		wallclock_ratio = 3;
+	} else if (max_ratio >= 4) {
+		dto_phase = 96 * 1000;
+		wallclock_ratio = 2;
+	} else if (max_ratio >= 2) {
+		dto_phase = 48 * 1000;
+		wallclock_ratio = 1;
+	} else {
+		dto_phase = 24 * 1000;
+		wallclock_ratio = 0;
+	}
+
 	/* there are two DTOs selected by DCCG_AUDIO_DTO_SELECT.
 	 * doesn't matter which one you use.  Just use the first one.
 	 */
@@ -243,12 +262,18 @@
 		 * practice it seems to cover DCE3.0 as well.
 		 */
 		if (dig->dig_encoder == 0) {
-			WREG32(DCCG_AUDIO_DTO0_PHASE, base_rate * 100);
-			WREG32(DCCG_AUDIO_DTO0_MODULE, clock * 100);
+			dto_cntl = RREG32(DCCG_AUDIO_DTO0_CNTL) & ~DCCG_AUDIO_DTO_WALLCLOCK_RATIO_MASK;
+			dto_cntl |= DCCG_AUDIO_DTO_WALLCLOCK_RATIO(wallclock_ratio);
+			WREG32(DCCG_AUDIO_DTO0_CNTL, dto_cntl);
+			WREG32(DCCG_AUDIO_DTO0_PHASE, dto_phase);
+			WREG32(DCCG_AUDIO_DTO0_MODULE, dto_modulo);
 			WREG32(DCCG_AUDIO_DTO_SELECT, 0); /* select DTO0 */
 		} else {
-			WREG32(DCCG_AUDIO_DTO1_PHASE, base_rate * 100);
-			WREG32(DCCG_AUDIO_DTO1_MODULE, clock * 100);
+			dto_cntl = RREG32(DCCG_AUDIO_DTO1_CNTL) & ~DCCG_AUDIO_DTO_WALLCLOCK_RATIO_MASK;
+			dto_cntl |= DCCG_AUDIO_DTO_WALLCLOCK_RATIO(wallclock_ratio);
+			WREG32(DCCG_AUDIO_DTO1_CNTL, dto_cntl);
+			WREG32(DCCG_AUDIO_DTO1_PHASE, dto_phase);
+			WREG32(DCCG_AUDIO_DTO1_MODULE, dto_modulo);
 			WREG32(DCCG_AUDIO_DTO_SELECT, 1); /* select DTO1 */
 		}
 	} else {