drm/radeon/kms: adjust evergreen display watermark setup

This patch fixes two issues:
- A disabled crtc does not use any lb, so return 0 for
lb size.  This makes the display priority calculation
more exact.
- Only use 1/2 and whole lb partitions. Using smaller
partitions can cause underflow to one of the displays
if you have multiple large displays on the same lb.

Fixes:
https://bugs.freedesktop.org/show_bug.cgi?id=34534Signed-off-by: Alex Deucher <alexdeucher@gmail.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/radeon/evergreen.c

@@ -353,7 +353,7 @@ static u32 evergreen_line_buffer_adjust(struct radeon_device *rdev,
 					struct drm_display_mode *mode,
 					struct drm_display_mode *other_mode)
 {
-	u32 tmp = 0;
+	u32 tmp;
 	/*
 	 * Line Buffer Setup
 	 * There are 3 line buffers, each one shared by 2 display controllers.
@@ -363,37 +363,32 @@ static u32 evergreen_line_buffer_adjust(struct radeon_device *rdev,
 	 * first display controller
 	 *  0 - first half of lb (3840 * 2)
 	 *  1 - first 3/4 of lb (5760 * 2)
-	 *  2 - whole lb (7680 * 2)
+	 *  2 - whole lb (7680 * 2), other crtc must be disabled
 	 *  3 - first 1/4 of lb (1920 * 2)
 	 * second display controller
 	 *  4 - second half of lb (3840 * 2)
 	 *  5 - second 3/4 of lb (5760 * 2)
-	 *  6 - whole lb (7680 * 2)
+	 *  6 - whole lb (7680 * 2), other crtc must be disabled
 	 *  7 - last 1/4 of lb (1920 * 2)
 	 */
-	if (mode && other_mode) {
-		if (mode->hdisplay > other_mode->hdisplay) {
-			if (mode->hdisplay > 2560)
-				tmp = 1; /* 3/4 */
-			else
+	/* this can get tricky if we have two large displays on a paired group
+	 * of crtcs.  Ideally for multiple large displays we'd assign them to
+	 * non-linked crtcs for maximum line buffer allocation.
+	 */
+	if (radeon_crtc->base.enabled && mode) {
+		if (other_mode)
 			tmp = 0; /* 1/2 */
-		} else if (other_mode->hdisplay > mode->hdisplay) {
-			if (other_mode->hdisplay > 2560)
-				tmp = 3; /* 1/4 */
 		else
-				tmp = 0; /* 1/2 */
-		} else
-			tmp = 0; /* 1/2 */
-	} else if (mode)
 			tmp = 2; /* whole */
-	else if (other_mode)
-		tmp = 3; /* 1/4 */
+	} else
+		tmp = 0;
 
 	/* second controller of the pair uses second half of the lb */
 	if (radeon_crtc->crtc_id % 2)
 		tmp += 4;
 	WREG32(DC_LB_MEMORY_SPLIT + radeon_crtc->crtc_offset, tmp);
 
+	if (radeon_crtc->base.enabled && mode) {
 		switch (tmp) {
 		case 0:
 		case 4:
@@ -421,6 +416,10 @@ static u32 evergreen_line_buffer_adjust(struct radeon_device *rdev,
 			else
 				return 1920 * 2;
 		}
+	}
+
+	/* controller not enabled, so no lb used */
+	return 0;
 }
 
 static u32 evergreen_get_number_of_dram_channels(struct radeon_device *rdev)