drm/radeon: Add a common function for DFS handling

Move encoding of DFS (digital frequency synthesizer) divider into a
separate function and improve calculation precision.

Signed-off-by: Slava Grigorev <slava.grigorev@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org

drivers/gpu/drm/radeon/dce6_afmt.c

@@ -304,18 +304,10 @@ void dce6_dp_audio_set_dto(struct radeon_device *rdev,
 		unsigned int div = (RREG32(DENTIST_DISPCLK_CNTL) &
 			DENTIST_DPREFCLK_WDIVIDER_MASK) >>
 			DENTIST_DPREFCLK_WDIVIDER_SHIFT;
-
-		if (div < 128 && div >= 96)
-			div -= 64;
-		else if (div >= 64)
-			div = div / 2 - 16;
-		else if (div >= 8)
-			div /= 4;
-		else
-			div = 0;
+		div = radeon_audio_decode_dfs_div(div);
 
 		if (div)
-			clock /= div;
+			clock = clock * 100 / div;
 
 		WREG32(DCE8_DCCG_AUDIO_DTO1_PHASE, 24000);
 		WREG32(DCE8_DCCG_AUDIO_DTO1_MODULE, clock);

drivers/gpu/drm/radeon/radeon_audio.c

@@ -775,3 +775,15 @@ void radeon_audio_dpms(struct drm_encoder *encoder, int mode)
 	if (radeon_encoder->audio && radeon_encoder->audio->dpms)
 		radeon_encoder->audio->dpms(encoder, mode == DRM_MODE_DPMS_ON);
 }
+
+unsigned int radeon_audio_decode_dfs_div(unsigned int div)
+{
+	if (div >= 8 && div < 64)
+		return (div - 8) * 25 + 200;
+	else if (div >= 64 && div < 96)
+		return (div - 64) * 50 + 1600;
+	else if (div >= 96 && div < 128)
+		return (div - 96) * 100 + 3200;
+	else
+		return 0;
+}

drivers/gpu/drm/radeon/radeon_audio.h

@@ -79,5 +79,6 @@ void radeon_audio_fini(struct radeon_device *rdev);
 void radeon_audio_mode_set(struct drm_encoder *encoder,
 	struct drm_display_mode *mode);
 void radeon_audio_dpms(struct drm_encoder *encoder, int mode);
+unsigned int radeon_audio_decode_dfs_div(unsigned int div);
 
 #endif