5.15-stable review patch. If anyone has any objections, please let me know.
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From: Wayne Lin Wayne.Lin@amd.com
[ Upstream commit 6bbce873a9c97cb12f5455c497be279ac58e707f ]
[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: 2f015ec6eab6 ("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... Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/gpu/drm/drm_dp_mst_topology.c | 8 ++++---- include/drm/drm_dp_mst_helper.h | 7 +++++++ 2 files changed, 11 insertions(+), 4 deletions(-)
diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c index 86e1a61b6b6df..70be5719e403b 100644 --- a/drivers/gpu/drm/drm_dp_mst_topology.c +++ b/drivers/gpu/drm/drm_dp_mst_topology.c @@ -178,13 +178,13 @@ 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/drm_dp_mst_helper.h b/include/drm/drm_dp_mst_helper.h index ddb9231d03097..9911264e0b155 100644 --- a/include/drm/drm_dp_mst_helper.h +++ b/include/drm/drm_dp_mst_helper.h @@ -232,6 +232,13 @@ 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;