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drm/dp_mst: Fix drm RAD print

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[ Upstream commit 6bbce873a9 ]

[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)

V3:
- Adjust the comment for rad[] so kdoc formats it properly (Lyude)

Fixes: 2f015ec6ea ("drm/dp_mst: Add sideband down request tracing + selftests")
Cc: Imre Deak <imre.deak@intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Harry Wentland <hwentlan@amd.com>
Cc: Lyude Paul <lyude@redhat.com>
Reviewed-by: Lyude Paul <lyude@redhat.com>
Signed-off-by: Wayne Lin <Wayne.Lin@amd.com>
Signed-off-by: Lyude Paul <lyude@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250113091100.3314533-2-Wayne.Lin@amd.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Wayne Lin 2025-01-13 17:10:59 +08:00 committed by Greg Kroah-Hartman
parent 5ffb6b9a1a
commit 69e90c1e33
2 changed files with 11 additions and 4 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

8
drivers/gpu/drm/display/drm_dp_mst_topology.c
View File

@ -179,13 +179,13 @@ 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

7
include/drm/display/drm_dp_mst_helper.h
View File

@ -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;