[PATCH 4.19 111/125] drm/amd/display: Passive DP->HDMI dongle detection fix

[Greg Kroah-Hartman]

From: Michael Strauss <michael.strauss@xxxxxxx>

[ Upstream commit bc2fde42e2418808dbfc04de1a6da91d7d31cf1a ]

[WHY]
i2c_read is called to differentiate passive DP->HDMI and DP->DVI-D dongles
The call is expected to fail in DVI-D case but pass in HDMI case
Some HDMI dongles have a chance to fail as well, causing misdetection as DVI-D

[HOW]
Retry i2c_read to ensure failed result is valid

Signed-off-by: Michael Strauss <michael.strauss@xxxxxxx>
Reviewed-by: Tony Cheng <Tony.Cheng@xxxxxxx>
Acked-by: Leo Li <sunpeng.li@xxxxxxx>
Signed-off-by: Alex Deucher <alexander.deucher@xxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 .../gpu/drm/amd/display/dc/core/dc_link_ddc.c | 24 ++++++++++++++-----
 1 file changed, 18 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/amd/display/dc/core/dc_link_ddc.c b/drivers/gpu/drm/amd/display/dc/core/dc_link_ddc.c
index 8def0d9fa0ff0..46c9cb47a96e5 100644
--- a/drivers/gpu/drm/amd/display/dc/core/dc_link_ddc.c
+++ b/drivers/gpu/drm/amd/display/dc/core/dc_link_ddc.c
@@ -433,6 +433,7 @@ void dal_ddc_service_i2c_query_dp_dual_mode_adaptor(
 	enum display_dongle_type *dongle = &sink_cap->dongle_type;
 	uint8_t type2_dongle_buf[DP_ADAPTOR_TYPE2_SIZE];
 	bool is_type2_dongle = false;
+	int retry_count = 2;
 	struct dp_hdmi_dongle_signature_data *dongle_signature;
 
 	/* Assume we have no valid DP passive dongle connected */
@@ -445,13 +446,24 @@ void dal_ddc_service_i2c_query_dp_dual_mode_adaptor(
 		DP_HDMI_DONGLE_ADDRESS,
 		type2_dongle_buf,
 		sizeof(type2_dongle_buf))) {
-		*dongle = DISPLAY_DONGLE_DP_DVI_DONGLE;
-		sink_cap->max_hdmi_pixel_clock = DP_ADAPTOR_DVI_MAX_TMDS_CLK;
+		/* Passive HDMI dongles can sometimes fail here without retrying*/
+		while (retry_count > 0) {
+			if (i2c_read(ddc,
+				DP_HDMI_DONGLE_ADDRESS,
+				type2_dongle_buf,
+				sizeof(type2_dongle_buf)))
+				break;
+			retry_count--;
+		}
+		if (retry_count == 0) {
+			*dongle = DISPLAY_DONGLE_DP_DVI_DONGLE;
+			sink_cap->max_hdmi_pixel_clock = DP_ADAPTOR_DVI_MAX_TMDS_CLK;
 
-		CONN_DATA_DETECT(ddc->link, type2_dongle_buf, sizeof(type2_dongle_buf),
-				"DP-DVI passive dongle %dMhz: ",
-				DP_ADAPTOR_DVI_MAX_TMDS_CLK / 1000);
-		return;
+			CONN_DATA_DETECT(ddc->link, type2_dongle_buf, sizeof(type2_dongle_buf),
+					"DP-DVI passive dongle %dMhz: ",
+					DP_ADAPTOR_DVI_MAX_TMDS_CLK / 1000);
+			return;
+		}
 	}
 
 	/* Check if Type 2 dongle.*/
-- 
2.20.1