drm/radeon: improve dac adjust heuristics for legacy pdac

Hopefully avoid more quirks in the future due to bogus
vbios dac data.

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

1 files changed, 4 insertions, 2 deletions

diff --git a/drivers/gpu/drm/radeon/radeon_combios.c b/drivers/gpu/drm/radeon/radeon_combios.c
index 8528b81cd64f..485f82c9929d 100644
--- a/drivers/gpu/drm/radeon/radeon_combios.c
+++ b/drivers/gpu/drm/radeon/radeon_combios.c
@@ -965,8 +965,10 @@ struct radeon_encoder_primary_dac *radeon_combios_get_primary_dac_info(struct
                         dac = RBIOS8(dac_info + 0x3) & 0xf;
                         p_dac->ps2_pdac_adj = (bg << 8) | (dac);
                 }
-                /* if the values are all zeros, use the table */
-                if (p_dac->ps2_pdac_adj)
+                /* if the values are zeros, use the table */
+                if ((dac == 0) || (bg == 0))
+                        found = 0;
+                else
                         found = 1;
         }