drm/radeon/kms: fix up DP clock programming on DCE4/5

In DP mode, the DP ref clock can come from PPLL, DCPLL, or ext clock,
depending on the asic.  The crtc virtual pixel clock is derived from
the DP ref clock.

- DCE4: PPLL or ext clock
- DCE5: DCPLL or ext clock

Setting ATOM_PPLL_INVALID will cause SetPixelClock to skip
PPLL/DCPLL programming and only program the DP DTO for the
crtc virtual pixel clock.
Signed-off-by: Alex Deucher <alexdeucher@gmail.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/radeon/atombios_crtc.c

@@ -1443,11 +1443,19 @@ static int radeon_atom_pick_pll(struct drm_crtc *crtc)
 	uint32_t pll_in_use = 0;
 
 	if (ASIC_IS_DCE4(rdev)) {
-		/* if crtc is driving DP and we have an ext clock, use that */
 		list_for_each_entry(test_encoder, &dev->mode_config.encoder_list, head) {
 			if (test_encoder->crtc && (test_encoder->crtc == crtc)) {
+				/* in DP mode, the DP ref clock can come from PPLL, DCPLL, or ext clock,
+				 * depending on the asic:
+				 * DCE4: PPLL or ext clock
+				 * DCE5: DCPLL or ext clock
+				 *
+				 * Setting ATOM_PPLL_INVALID will cause SetPixelClock to skip
+				 * PPLL/DCPLL programming and only program the DP DTO for the
+				 * crtc virtual pixel clock.
+				 */
 				if (atombios_get_encoder_mode(test_encoder) == ATOM_ENCODER_MODE_DP) {
-					if (rdev->clock.dp_extclk)
+					if (ASIC_IS_DCE5(rdev) || rdev->clock.dp_extclk)
 						return ATOM_PPLL_INVALID;
 				}
 			}

drivers/gpu/drm/radeon/radeon_encoders.c

@@ -988,11 +988,16 @@ atombios_dig_transmitter_setup(struct drm_encoder *encoder, int action, uint8_t
 		}
 
 		if (ASIC_IS_DCE5(rdev)) {
-			if (is_dp && rdev->clock.dp_extclk)
-				args.v4.acConfig.ucRefClkSource = 3; /* external src */
+			/* On DCE5 DCPLL usually generates the DP ref clock */
+			if (is_dp) {
+				if (rdev->clock.dp_extclk)
+					args.v4.acConfig.ucRefClkSource = ENCODER_REFCLK_SRC_EXTCLK;
 				else
+					args.v4.acConfig.ucRefClkSource = ENCODER_REFCLK_SRC_DCPLL;
+			} else
 				args.v4.acConfig.ucRefClkSource = pll_id;
 		} else {
+			/* On DCE4, if there is an external clock, it generates the DP ref clock */
 			if (is_dp && rdev->clock.dp_extclk)
 				args.v3.acConfig.ucRefClkSource = 2; /* external src */
 			else