[PATCH 3.16 070/114] drm/radeon: make sure vertical front porch is at least 1

[Ben Hutchings]

3.16.36-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Alex Deucher <alexander.deucher@xxxxxxx>

commit 3104b8128d4d646a574ed9d5b17c7d10752cd70b upstream.

hw doesn't like a 0 value.

Signed-off-by: Alex Deucher <alexander.deucher@xxxxxxx>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 drivers/gpu/drm/radeon/atombios_encoders.c | 4 ++++
 1 file changed, 4 insertions(+)

--- a/drivers/gpu/drm/radeon/atombios_encoders.c
+++ b/drivers/gpu/drm/radeon/atombios_encoders.c
@@ -332,6 +332,10 @@ static bool radeon_atom_mode_fixup(struc
 	    && (mode->crtc_vsync_start < (mode->crtc_vdisplay + 2)))
 		adjusted_mode->crtc_vsync_start = adjusted_mode->crtc_vdisplay + 2;
 
+	/* vertical FP must be at least 1 */
+	if (mode->crtc_vsync_start == mode->crtc_vdisplay)
+		adjusted_mode->crtc_vsync_start++;
+
 	/* get the native mode for LVDS */
 	if (radeon_encoder->active_device & (ATOM_DEVICE_LCD_SUPPORT))
 		radeon_panel_mode_fixup(encoder, adjusted_mode);