[PATCH 05/23] drm/amd/display: Get LTTPR IEEE OUI/Device ID From Closest LTTPR To Host
Alex Hung
alex.hung at amd.com
Wed Jun 4 18:43:16 UTC 2025
From: Michael Strauss <michael.strauss at amd.com>
[WHY]
These fields are read for the explicit purpose of detecting embedded LTTPRs
(i.e. between host ASIC and the user-facing port), and thus need to
calculate the correct DPCD address offset based on LTTPR count to target
the appropriate LTTPR's DPCD register space with these queries.
[HOW]
Cascaded LTTPRs in a link each snoop and increment LTTPR count when queried
via DPCD read, so an LTTPR embedded in a source device (e.g. USB4 port on a
laptop) will always be addressible using the max LTTPR count seen by the
host. Therefore we simply need to use a recently added helper function to
calculate the correct DPCD address to target potentially embedded LTTPRs
based on the received LTTPR count.
Cc: Mario Limonciello <mario.limonciello at amd.com>
Cc: Alex Deucher <alexander.deucher at amd.com>
Cc: stable at vger.kernel.org
Reviewed-by: Wenjing Liu <wenjing.liu at amd.com>
Signed-off-by: Michael Strauss <michael.strauss at amd.com>
Signed-off-by: Alex Hung <alex.hung at amd.com>
---
drivers/gpu/drm/amd/display/dc/dc_dp_types.h | 4 +-
.../dc/link/protocols/link_dp_capability.c | 38 +++++++++++++++----
2 files changed, 33 insertions(+), 9 deletions(-)
diff --git a/drivers/gpu/drm/amd/display/dc/dc_dp_types.h b/drivers/gpu/drm/amd/display/dc/dc_dp_types.h
index 0bad8304ccf6..d346f8ae1634 100644
--- a/drivers/gpu/drm/amd/display/dc/dc_dp_types.h
+++ b/drivers/gpu/drm/amd/display/dc/dc_dp_types.h
@@ -1172,8 +1172,8 @@ struct dc_lttpr_caps {
union dp_128b_132b_supported_lttpr_link_rates supported_128b_132b_rates;
union dp_alpm_lttpr_cap alpm;
uint8_t aux_rd_interval[MAX_REPEATER_CNT - 1];
- uint8_t lttpr_ieee_oui[3];
- uint8_t lttpr_device_id[6];
+ uint8_t lttpr_ieee_oui[3]; // Always read from closest LTTPR to host
+ uint8_t lttpr_device_id[6]; // Always read from closest LTTPR to host
};
struct dc_dongle_dfp_cap_ext {
diff --git a/drivers/gpu/drm/amd/display/dc/link/protocols/link_dp_capability.c b/drivers/gpu/drm/amd/display/dc/link/protocols/link_dp_capability.c
index a5127c2d47ef..0f965380a9b4 100644
--- a/drivers/gpu/drm/amd/display/dc/link/protocols/link_dp_capability.c
+++ b/drivers/gpu/drm/amd/display/dc/link/protocols/link_dp_capability.c
@@ -385,9 +385,15 @@ bool dp_is_128b_132b_signal(struct pipe_ctx *pipe_ctx)
bool dp_is_lttpr_present(struct dc_link *link)
{
/* Some sink devices report invalid LTTPR revision, so don't validate against that cap */
- return (dp_parse_lttpr_repeater_count(link->dpcd_caps.lttpr_caps.phy_repeater_cnt) != 0 &&
+ uint32_t lttpr_count = dp_parse_lttpr_repeater_count(link->dpcd_caps.lttpr_caps.phy_repeater_cnt);
+ bool is_lttpr_present = (lttpr_count > 0 &&
link->dpcd_caps.lttpr_caps.max_lane_count > 0 &&
link->dpcd_caps.lttpr_caps.max_lane_count <= 4);
+
+ if (lttpr_count > 0 && !is_lttpr_present)
+ DC_LOG_ERROR("LTTPR count is nonzero but invalid lane count reported. Assuming no LTTPR present.\n");
+
+ return is_lttpr_present;
}
/* in DP compliance test, DPR-120 may have
@@ -1551,6 +1557,8 @@ enum dc_status dp_retrieve_lttpr_cap(struct dc_link *link)
uint8_t lttpr_dpcd_data[10] = {0};
enum dc_status status;
bool is_lttpr_present;
+ uint32_t lttpr_count;
+ uint32_t closest_lttpr_offset;
/* Logic to determine LTTPR support*/
bool vbios_lttpr_interop = link->dc->caps.vbios_lttpr_aware;
@@ -1602,20 +1610,22 @@ enum dc_status dp_retrieve_lttpr_cap(struct dc_link *link)
lttpr_dpcd_data[DP_LTTPR_ALPM_CAPABILITIES -
DP_LT_TUNABLE_PHY_REPEATER_FIELD_DATA_STRUCTURE_REV];
+ lttpr_count = dp_parse_lttpr_repeater_count(link->dpcd_caps.lttpr_caps.phy_repeater_cnt);
+
/* If this chip cap is set, at least one retimer must exist in the chain
* Override count to 1 if we receive a known bad count (0 or an invalid value) */
if (((link->chip_caps & AMD_EXT_DISPLAY_PATH_CAPS__EXT_CHIP_MASK) == AMD_EXT_DISPLAY_PATH_CAPS__DP_FIXED_VS_EN) &&
- (dp_parse_lttpr_repeater_count(link->dpcd_caps.lttpr_caps.phy_repeater_cnt) == 0)) {
+ lttpr_count == 0) {
/* If you see this message consistently, either the host platform has FIXED_VS flag
* incorrectly configured or the sink device is returning an invalid count.
*/
DC_LOG_ERROR("lttpr_caps phy_repeater_cnt is 0x%x, forcing it to 0x80.",
link->dpcd_caps.lttpr_caps.phy_repeater_cnt);
link->dpcd_caps.lttpr_caps.phy_repeater_cnt = 0x80;
+ lttpr_count = 1;
DC_LOG_DC("lttpr_caps forced phy_repeater_cnt = %d\n", link->dpcd_caps.lttpr_caps.phy_repeater_cnt);
}
- /* Attempt to train in LTTPR transparent mode if repeater count exceeds 8. */
is_lttpr_present = dp_is_lttpr_present(link);
DC_LOG_DC("is_lttpr_present = %d\n", is_lttpr_present);
@@ -1623,11 +1633,25 @@ enum dc_status dp_retrieve_lttpr_cap(struct dc_link *link)
if (is_lttpr_present) {
CONN_DATA_DETECT(link, lttpr_dpcd_data, sizeof(lttpr_dpcd_data), "LTTPR Caps: ");
- core_link_read_dpcd(link, DP_LTTPR_IEEE_OUI, link->dpcd_caps.lttpr_caps.lttpr_ieee_oui, sizeof(link->dpcd_caps.lttpr_caps.lttpr_ieee_oui));
- CONN_DATA_DETECT(link, link->dpcd_caps.lttpr_caps.lttpr_ieee_oui, sizeof(link->dpcd_caps.lttpr_caps.lttpr_ieee_oui), "LTTPR IEEE OUI: ");
+ // Identify closest LTTPR to determine if workarounds required for known embedded LTTPR
+ closest_lttpr_offset = dp_get_closest_lttpr_offset(lttpr_count);
- core_link_read_dpcd(link, DP_LTTPR_DEVICE_ID, link->dpcd_caps.lttpr_caps.lttpr_device_id, sizeof(link->dpcd_caps.lttpr_caps.lttpr_device_id));
- CONN_DATA_DETECT(link, link->dpcd_caps.lttpr_caps.lttpr_device_id, sizeof(link->dpcd_caps.lttpr_caps.lttpr_device_id), "LTTPR Device ID: ");
+ core_link_read_dpcd(link, (DP_LTTPR_IEEE_OUI + closest_lttpr_offset),
+ link->dpcd_caps.lttpr_caps.lttpr_ieee_oui, sizeof(link->dpcd_caps.lttpr_caps.lttpr_ieee_oui));
+ core_link_read_dpcd(link, (DP_LTTPR_DEVICE_ID + closest_lttpr_offset),
+ link->dpcd_caps.lttpr_caps.lttpr_device_id, sizeof(link->dpcd_caps.lttpr_caps.lttpr_device_id));
+
+ if (lttpr_count > 1) {
+ CONN_DATA_DETECT(link, link->dpcd_caps.lttpr_caps.lttpr_ieee_oui, sizeof(link->dpcd_caps.lttpr_caps.lttpr_ieee_oui),
+ "Closest LTTPR To Host's IEEE OUI: ");
+ CONN_DATA_DETECT(link, link->dpcd_caps.lttpr_caps.lttpr_device_id, sizeof(link->dpcd_caps.lttpr_caps.lttpr_device_id),
+ "Closest LTTPR To Host's LTTPR Device ID: ");
+ } else {
+ CONN_DATA_DETECT(link, link->dpcd_caps.lttpr_caps.lttpr_ieee_oui, sizeof(link->dpcd_caps.lttpr_caps.lttpr_ieee_oui),
+ "LTTPR IEEE OUI: ");
+ CONN_DATA_DETECT(link, link->dpcd_caps.lttpr_caps.lttpr_device_id, sizeof(link->dpcd_caps.lttpr_caps.lttpr_device_id),
+ "LTTPR Device ID: ");
+ }
}
return status;
--
2.43.0
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