FAILED: patch "[PATCH] drm/amd/display: Get LTTPR IEEE OUI/Device ID From Closest" failed to apply to 6.15-stable tree

[<gregkh@linuxfoundation.org>]

The patch below does not apply to the 6.15-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.15.y
git checkout FETCH_HEAD
git cherry-pick -x d358a51444c88bcc995e471dc8cc840f19e4b374
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2025063005-crop-granular-c1cb@gregkh' --subject-prefix 'PATCH 6.15.y' HEAD^..

Possible dependencies:



thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From d358a51444c88bcc995e471dc8cc840f19e4b374 Mon Sep 17 00:00:00 2001
From: Michael Strauss <michael.strauss@amd.com>
Date: Wed, 26 Feb 2025 10:03:48 -0500
Subject: [PATCH] drm/amd/display: Get LTTPR IEEE OUI/Device ID From Closest
 LTTPR To Host

[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@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Wenjing Liu <wenjing.liu@amd.com>
Signed-off-by: Michael Strauss <michael.strauss@amd.com>
Signed-off-by: Alex Hung <alex.hung@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit 791897f5c77a2a65d0e500be4743af2ddf6eb061)
Cc: stable@vger.kernel.org

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;