[Why]
The RAD of sideband message printed today is incorrect.
For RAD stored within MST branch
- If MST branch LCT is 1, it's RAD array is untouched and remained as 0.
- If MST branch LCT is larger than 1, use nibble to store the up facing
port number in cascaded sequence as illustrated below:
u8 RAD[0] = (LCT_2_UFP << 4) | LCT_3_UFP
RAD[1] = (LCT_4_UFP << 4) | LCT_5_UFP
...
In drm_dp_mst_rad_to_str(), it wrongly to use BIT_MASK(4) to fetch the port
number of one nibble.
[How]
Adjust the code by:
- RAD array items are valuable only for LCT >= 1.
- Use 0xF as the mask to replace BIT_MASK(4)
V2:
- Document how RAD is constructed (Imre)
Fixes: 2f015ec6eab6 ("drm/dp_mst: Add sideband down request tracing +
selftests")
Cc: Imre Deak <imre.d...@intel.com>
Cc: Ville Syrjälä <ville.syrj...@linux.intel.com>
Cc: Harry Wentland <hwent...@amd.com>
Cc: Lyude Paul <ly...@redhat.com>
Signed-off-by: Wayne Lin <wayne....@amd.com>
---
drivers/gpu/drm/display/drm_dp_mst_topology.c | 8 ++++----
include/drm/display/drm_dp_mst_helper.h | 7 +++++++
2 files changed, 11 insertions(+), 4 deletions(-)
diff --git a/drivers/gpu/drm/display/drm_dp_mst_topology.c
b/drivers/gpu/drm/display/drm_dp_mst_topology.c
index f8cd094efa3c..271a00b81264 100644
--- a/drivers/gpu/drm/display/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/display/drm_dp_mst_topology.c
@@ -175,13 +175,13 @@ static int
drm_dp_mst_rad_to_str(const u8 rad[8], u8 lct, char *out, size_t len)
{
int i;
- u8 unpacked_rad[16];
+ u8 unpacked_rad[16] = {};
- for (i = 0; i < lct; i++) {
+ for (i = 1; i < lct; i++) {
if (i % 2)
- unpacked_rad[i] = rad[i / 2] >> 4;
+ unpacked_rad[i] = rad[(i - 1) / 2] >> 4;
else
- unpacked_rad[i] = rad[i / 2] & BIT_MASK(4);
+ unpacked_rad[i] = rad[(i - 1) / 2] & 0xF;
}
/* TODO: Eventually add something to printk so we can format the rad
diff --git a/include/drm/display/drm_dp_mst_helper.h
b/include/drm/display/drm_dp_mst_helper.h
index a80ba457a858..fdf9b8647592 100644
--- a/include/drm/display/drm_dp_mst_helper.h
+++ b/include/drm/display/drm_dp_mst_helper.h
@@ -222,6 +222,13 @@ struct drm_dp_mst_branch {
*/
struct list_head destroy_next;
+ /**
+ * @rad: Relative Address of the MST branch.
+ * For drm_dp_mst_topology_mgr::mst_primary, it's rad[8] are all 0,
+ * unset and unused. For MST branches connected after mst_primary,
+ * in each element of rad[] the nibbles are ordered by the most
+ * signifcant 4 bits first and the least significant 4 bits second.
+ */
u8 rad[8];
u8 lct;
int num_ports;
--
2.37.3
