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drm/amd/display: Add dp_skip_rbr flag for NUTMEG

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No functional changes. Just clean up a conceptual mismatch.

Based on feedback on the NUTMEG code in DC, the
preferred_link_setting is meant to force the DP link to a
specific setting, meaning both the link rate and lane count
should be locked to an exact value. What NUTMEG needs is
a lower bound on the link rate, which is not the same concept.

Implement this as a HW workaround flag instead.

Suggested-by: Wenjing Liu <wenjing.liu@amd.com>
Signed-off-by: Timur Kristóf <timur.kristof@gmail.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit 871ceb853841bcaa4e6cec3723b16c4887a760be)
Cc: stable@vger.kernel.org
This commit is contained in:
Timur Kristóf 2026-05-29 11:09:09 +02:00 committed by Alex Deucher
parent 9fb646bc4d
commit e39b7cf5c6
3 changed files with 6 additions and 4 deletions
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2
drivers/gpu/drm/amd/display/dc/dc.h
View File

@ -1815,6 +1815,8 @@ struct dc_scratch_space {
bool dp_skip_DID2;
bool dp_skip_reset_segment;
bool dp_skip_fs_144hz;
/* Some DP bridges don't work with RBR and must use HBR. */
bool dp_skip_rbr;
bool dp_mot_reset_segment;
/* Some USB4 docks do not handle turning off MST DSC once it has been enabled. */
bool dpia_mst_dsc_always_on;

2
drivers/gpu/drm/amd/display/dc/link/link_detection.c
View File

@ -623,7 +623,7 @@ static bool detect_dp(struct dc_link *link,
link->dpcd_caps.sink_count.bits.SINK_COUNT = 1;
/* NUTMEG requires that we use HBR, doesn't work with RBR. */
if (link->dpcd_caps.branch_dev_id == DP_BRANCH_DEVICE_ID_00001A)
link->preferred_link_setting.link_rate = LINK_RATE_HIGH;
link->wa_flags.dp_skip_rbr = true;
}
return true;

6
drivers/gpu/drm/amd/display/dc/link/protocols/link_dp_capability.c
View File

@ -750,9 +750,9 @@ static bool decide_dp_link_settings(struct dc_link *link, struct dc_link_setting
if (req_bw > dp_link_bandwidth_kbps(link, &link->verified_link_cap))
return false;
if (link->preferred_link_setting.link_rate != LINK_RATE_UNKNOWN) {
initial_link_setting.link_rate = link->preferred_link_setting.link_rate;
current_link_setting.link_rate = link->preferred_link_setting.link_rate;
if (link->wa_flags.dp_skip_rbr) {
initial_link_setting.link_rate = LINK_RATE_HIGH;
current_link_setting.link_rate = LINK_RATE_HIGH;
}
/* search for the minimum link setting that: