linux-kernel - [PATCH AUTOSEL 6.12 016/107] drm/amd/display: Block UHBR Based On USB-C PD Cable ID

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Message-ID: <20241124133301.3341829-16-sashal@kernel.org>
Date: Sun, 24 Nov 2024 08:28:36 -0500
From: Sasha Levin <sashal@...nel.org>
To: linux-kernel@...r.kernel.org,
	stable@...r.kernel.org
Cc: Michael Strauss <michael.strauss@....com>,
	Wenjing Liu <wenjing.liu@....com>,
	Ovidiu Bunea <ovidiu.bunea@....com>,
	Aurabindo Pillai <aurabindo.pillai@....com>,
	Daniel Wheeler <daniel.wheeler@....com>,
	Alex Deucher <alexander.deucher@....com>,
	Sasha Levin <sashal@...nel.org>,
	harry.wentland@....com,
	sunpeng.li@....com,
	Rodrigo.Siqueira@....com,
	christian.koenig@....com,
	Xinhui.Pan@....com,
	airlied@...il.com,
	simona@...ll.ch,
	alex.hung@....com,
	george.shen@....com,
	daniel.sa@....com,
	Ausef.Yousof@....com,
	amd-gfx@...ts.freedesktop.org,
	dri-devel@...ts.freedesktop.org
Subject: [PATCH AUTOSEL 6.12 016/107] drm/amd/display: Block UHBR Based On USB-C PD Cable ID

From: Michael Strauss <michael.strauss@....com>

[ Upstream commit 4f01a68751194d05280d659a65758c09e4af04d6 ]

[WHY]
Currently the absence of UHBR cable ID caps from USB-C PD does not block UHBR
rates. In situations where DPCD reports valid UHBR capability but USB-C PD
does not, such as using a USB-C to DP1.4 dongle connected to a native DP2.1
cable, link loss and lightup failures can be seen as a result.

Additionally, in edge cases where a platform supports cable ID but DMUB
doesn't correctly return cable ID caps, driver currently also allows UHBR.

[HOW]
Block UHBR rates over DP alt mode if cable id indicates no UHBR support.
Additionally, block UHBR rates if a cable ID supported platform receives no
reply from a DMUB cable id query.

Reviewed-by: Wenjing Liu <wenjing.liu@....com>
Reviewed-by: Ovidiu Bunea <ovidiu.bunea@....com>
Signed-off-by: Michael Strauss <michael.strauss@....com>
Signed-off-by: Aurabindo Pillai <aurabindo.pillai@....com>
Tested-by: Daniel Wheeler <daniel.wheeler@....com>
Signed-off-by: Alex Deucher <alexander.deucher@....com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 .../dc/link/protocols/link_dp_capability.c    | 22 ++++++++++++++-----
 1 file changed, 16 insertions(+), 6 deletions(-)

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 d78c8ec4de79e..fe4aa2c158eae 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
@@ -1409,7 +1409,8 @@ static bool get_usbc_cable_id(struct dc_link *link, union dp_cable_id *cable_id)
 
 	if (!link->ctx->dmub_srv ||
 			link->ep_type != DISPLAY_ENDPOINT_PHY ||
-			link->link_enc->features.flags.bits.DP_IS_USB_C == 0)
+			link->link_enc->features.flags.bits.DP_IS_USB_C == 0 ||
+			link->link_enc->features.flags.bits.IS_DP2_CAPABLE == 0)
 		return false;
 
 	memset(&cmd, 0, sizeof(cmd));
@@ -1422,7 +1423,9 @@ static bool get_usbc_cable_id(struct dc_link *link, union dp_cable_id *cable_id)
 		cable_id->raw = cmd.cable_id.data.output_raw;
 		DC_LOG_DC("usbc_cable_id = %d.\n", cable_id->raw);
 	}
-	return cmd.cable_id.header.ret_status == 1;
+
+	ASSERT(cmd.cable_id.header.ret_status);
+	return true;
 }
 
 static void retrieve_cable_id(struct dc_link *link)
@@ -2103,6 +2106,8 @@ struct dc_link_settings dp_get_max_link_cap(struct dc_link *link)
 	/* get max link encoder capability */
 	if (link_enc)
 		link_enc->funcs->get_max_link_cap(link_enc, &max_link_cap);
+	else
+		return max_link_cap;
 
 	/* Lower link settings based on sink's link cap */
 	if (link->reported_link_cap.lane_count < max_link_cap.lane_count)
@@ -2136,10 +2141,15 @@ struct dc_link_settings dp_get_max_link_cap(struct dc_link *link)
 	 */
 	cable_max_link_rate = get_cable_max_link_rate(link);
 
-	if (!link->dc->debug.ignore_cable_id &&
-			cable_max_link_rate != LINK_RATE_UNKNOWN) {
-		if (cable_max_link_rate < max_link_cap.link_rate)
-			max_link_cap.link_rate = cable_max_link_rate;
+	if (!link->dc->debug.ignore_cable_id) {
+		if (cable_max_link_rate != LINK_RATE_UNKNOWN)
+			// cable max link rate known
+			max_link_cap.link_rate = MIN(max_link_cap.link_rate, cable_max_link_rate);
+		else if (link_enc->funcs->is_in_alt_mode && link_enc->funcs->is_in_alt_mode(link_enc))
+			// cable max link rate ambiguous, DP alt mode, limit to HBR3
+			max_link_cap.link_rate = MIN(max_link_cap.link_rate, LINK_RATE_HIGH3);
+		//else {}
+			// cable max link rate ambiguous, DP, do nothing
 
 		if (!link->dpcd_caps.cable_id.bits.UHBR13_5_CAPABILITY &&
 				link->dpcd_caps.cable_id.bits.CABLE_TYPE >= 2)
-- 
2.43.0