drm/radeon/combios: add some validation of lvds values

Fixes a broken hsync start value uncovered by:
abc0b1447d4974963548777a5ba4a4457c82c426
(drm: Perform basic sanity checks on probed modes)

The driver handled the bad hsync start elsewhere, but
the above commit prevented it from getting added.

bug:
https://bugs.freedesktop.org/show_bug.cgi?id=91401

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

1 files changed, 6 insertions, 1 deletions

diff --git a/drivers/gpu/drm/radeon/radeon_combios.c b/drivers/gpu/drm/radeon/radeon_combios.c
index 3e5f6b71f3ad..c097d3a82bda 100644
--- a/drivers/gpu/drm/radeon/radeon_combios.c
+++ b/drivers/gpu/drm/radeon/radeon_combios.c
@@ -1255,10 +1255,15 @@ struct radeon_encoder_lvds *radeon_combios_get_lvds_info(struct radeon_encoder
 
                         if ((RBIOS16(tmp) == lvds->native_mode.hdisplay) &&
                             (RBIOS16(tmp + 2) == lvds->native_mode.vdisplay)) {
+                                u32 hss = (RBIOS16(tmp + 21) - RBIOS16(tmp + 19) - 1) * 8;
+
+                                if (hss > lvds->native_mode.hdisplay)
+                                        hss = (10 - 1) * 8;
+
                                 lvds->native_mode.htotal = lvds->native_mode.hdisplay +
                                         (RBIOS16(tmp + 17) - RBIOS16(tmp + 19)) * 8;
                                 lvds->native_mode.hsync_start = lvds->native_mode.hdisplay +
-                                        (RBIOS16(tmp + 21) - RBIOS16(tmp + 19) - 1) * 8;
+                                        hss;
                                 lvds->native_mode.hsync_end = lvds->native_mode.hsync_start +
                                         (RBIOS8(tmp + 23) * 8);