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drm/amd/display: Update FIXED_VS Link Rate Toggle Workaround Usage

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[WHY]
Previously the 128b/132b LTTPR support DPCD field was used to decide if
FIXED_VS training sequence required a rate toggle before initiating LT.

When running DP2.1 4.9.x.x compliance tests, emulated LTTPRs can report
no-128b/132b support which is then forwarded by the FIXED_VS retimer.
As a result this test exposes the rate toggle again, erroneously causing
failures as certain compliance sinks don't expect this behaviour.

[HOW]
Add new DPCD register defines/reads to read LTTPR IEEE OUI and device ID.

Decide whether to perform the rate toggle based on the LTTPR's IEEE OUI
which guarantees that we only perform the toggle on affected retimers.

Reviewed-by: Wenjing Liu <wenjing.liu@amd.com>
Signed-off-by: Michael Strauss <michael.strauss@amd.com>
Signed-off-by: Zaeem Mohamed <zaeem.mohamed@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
This commit is contained in:
Michael Strauss 2025-01-24 15:02:27 -05:00 committed by Alex Deucher
parent 23ef388a84
commit 7c6518c1c7
3 changed files with 20 additions and 3 deletions
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8
drivers/gpu/drm/amd/display/dc/dc_dp_types.h
View File

@ -1128,6 +1128,8 @@ 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];
};
struct dc_dongle_dfp_cap_ext {
@ -1391,6 +1393,12 @@ struct dp_trace {
#ifndef DP_BRANCH_VENDOR_SPECIFIC_START
#define DP_BRANCH_VENDOR_SPECIFIC_START 0x50C
#endif
#ifndef DP_LTTPR_IEEE_OUI
#define DP_LTTPR_IEEE_OUI 0xF003D
#endif
#ifndef DP_LTTPR_DEVICE_ID
#define DP_LTTPR_DEVICE_ID 0xF0040
#endif
/** USB4 DPCD BW Allocation Registers Chapter 10.7 **/
#ifndef DP_TUNNELING_CAPABILITIES
#define DP_TUNNELING_CAPABILITIES 0xE000D /* 1.4a */

12
drivers/gpu/drm/amd/display/dc/link/protocols/link_dp_capability.c
View File

@ -1575,10 +1575,18 @@ enum dc_status dp_retrieve_lttpr_cap(struct dc_link *link)
/* Attempt to train in LTTPR transparent mode if repeater count exceeds 8. */
is_lttpr_present = dp_is_lttpr_present(link);
if (is_lttpr_present)
DC_LOG_DC("is_lttpr_present = %d\n", is_lttpr_present);
if (is_lttpr_present) {
CONN_DATA_DETECT(link, lttpr_dpcd_data, sizeof(lttpr_dpcd_data), "LTTPR Caps: ");
DC_LOG_DC("is_lttpr_present = %d\n", is_lttpr_present);
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: ");
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: ");
}
return status;
}

3
drivers/gpu/drm/amd/display/dc/link/protocols/link_dp_training_fixed_vs_pe_retimer.c
View File

@ -270,7 +270,8 @@ enum link_training_result dp_perform_fixed_vs_pe_training_sequence(
rate = get_dpcd_link_rate(&lt_settings->link_settings);
if (!link->dpcd_caps.lttpr_caps.main_link_channel_coding.bits.DP_128b_132b_SUPPORTED) {
// Only perform toggle if FIXED_VS LTTPR reports no IEEE OUI
if (memcmp("\x0,\x0,\x0", &link->dpcd_caps.lttpr_caps.lttpr_ieee_oui[0], 3) == 0) {
/* Vendor specific: Toggle link rate */
toggle_rate = (rate == 0x6) ? 0xA : 0x6;