drm/radeon/kms: workaround invalid AVI infoframe checksum issue

This change was verified to fix both issues with no video I've
investigated. I've also checked checksum calculation with fglrx on:
RV620, HD54xx, HD5450, HD6310, HD6320.

Cc: stable@vger.kernel.org
Signed-off-by: Rafał Miłecki <zajec5@gmail.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

1 files changed, 7 insertions, 0 deletions

diff --git a/drivers/gpu/drm/radeon/r600_hdmi.c b/drivers/gpu/drm/radeon/r600_hdmi.c
index 5c805f7fea39..2c70a85e72c6 100644
--- a/drivers/gpu/drm/radeon/r600_hdmi.c
+++ b/drivers/gpu/drm/radeon/r600_hdmi.c
@@ -196,6 +196,13 @@ static void r600_hdmi_videoinfoframe(
         frame[0xD] = (right_bar >> 8);
 
         r600_hdmi_infoframe_checksum(0x82, 0x02, 0x0D, frame);
+        /* Our header values (type, version, length) should be alright, Intel
+         * is using the same. Checksum function also seems to be OK, it works
+         * fine for audio infoframe. However calculated value is always lower
+         * by 2 in comparison to fglrx. It breaks displaying anything in case
+         * of TVs that strictly check the checksum. Hack it manually here to
+         * workaround this issue. */
+        frame[0x0] += 2;
 
         WREG32(offset+R600_HDMI_VIDEOINFOFRAME_0,
                 frame[0x0] | (frame[0x1] << 8) | (frame[0x2] << 16) | (frame[0x3] << 24));