drm/radeon: use frac fb div on RS780/RS880

Monitors seem to prefer it.  Fixes:
https://bugs.freedesktop.org/show_bug.cgi?id=37696

Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org

1 files changed, 3 insertions, 0 deletions

diff --git a/drivers/gpu/drm/radeon/atombios_crtc.c b/drivers/gpu/drm/radeon/atombios_crtc.c
index 21a892c6ab9c..6d6fdb3ba0d0 100644
--- a/drivers/gpu/drm/radeon/atombios_crtc.c
+++ b/drivers/gpu/drm/radeon/atombios_crtc.c
@@ -557,6 +557,9 @@ static u32 atombios_adjust_pll(struct drm_crtc *crtc,
                 /* use frac fb div on APUs */
                 if (ASIC_IS_DCE41(rdev) || ASIC_IS_DCE61(rdev))
                         radeon_crtc->pll_flags |= RADEON_PLL_USE_FRAC_FB_DIV;
+                /* use frac fb div on RS780/RS880 */
+                if ((rdev->family == CHIP_RS780) || (rdev->family == CHIP_RS880))
+                        radeon_crtc->pll_flags |= RADEON_PLL_USE_FRAC_FB_DIV;
                 if (ASIC_IS_DCE32(rdev) && mode->clock > 165000)
                         radeon_crtc->pll_flags |= RADEON_PLL_USE_FRAC_FB_DIV;
         } else {