[PATCH AUTOSEL 4.20 218/304] drm/amd/display: Add retry to read ddc_clock pin

[Sasha Levin <sashal@kernel.org>]

From: Paul Hsieh <paul.hsieh@amd.com>

[ Upstream commit bd4905a9583c760da31ded7256dca6f71483c3dc ]

[WHY]
On customer board, there is one pluse (1v , < 1ms) on
DDC_CLK pin when plug / unplug DP cable. Driver will read
it and config DP to HDMI/DVI dongle.

[HOW]
If there is a real dongle, DDC_CLK should be always pull high.
Try to read again to recovery this special case. Retry times = 3.
Need additional 3ms to detect DP passive dongle(3 failures)

Signed-off-by: Paul Hsieh <paul.hsieh@amd.com>
Reviewed-by: Eric Yang <eric.yang2@amd.com>
Acked-by: Leo Li <sunpeng.li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/gpu/drm/amd/display/dc/core/dc_link.c | 23 ++++++++++++++-----
 1 file changed, 17 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/amd/display/dc/core/dc_link.c b/drivers/gpu/drm/amd/display/dc/core/dc_link.c
index 5141c1401889..ef1b350a45e0 100644
--- a/drivers/gpu/drm/amd/display/dc/core/dc_link.c
+++ b/drivers/gpu/drm/amd/display/dc/core/dc_link.c
@@ -332,7 +332,7 @@ bool dc_link_is_dp_sink_present(struct dc_link *link)
 {
 	enum gpio_result gpio_result;
 	uint32_t clock_pin = 0;
-
+	uint8_t retry = 0;
 	struct ddc *ddc;
 
 	enum connector_id connector_id =
@@ -361,11 +361,22 @@ bool dc_link_is_dp_sink_present(struct dc_link *link)
 		return present;
 	}
 
-	/* Read GPIO: DP sink is present if both clock and data pins are zero */
-	/* [anaumov] in DAL2, there was no check for GPIO failure */
-
-	gpio_result = dal_gpio_get_value(ddc->pin_clock, &clock_pin);
-	ASSERT(gpio_result == GPIO_RESULT_OK);
+	/*
+	 * Read GPIO: DP sink is present if both clock and data pins are zero
+	 *
+	 * [W/A] plug-unplug DP cable, sometimes customer board has
+	 * one short pulse on clk_pin(1V, < 1ms). DP will be config to HDMI/DVI
+	 * then monitor can't br light up. Add retry 3 times
+	 * But in real passive dongle, it need additional 3ms to detect
+	 */
+	do {
+		gpio_result = dal_gpio_get_value(ddc->pin_clock, &clock_pin);
+		ASSERT(gpio_result == GPIO_RESULT_OK);
+		if (clock_pin)
+			udelay(1000);
+		else
+			break;
+	} while (retry++ < 3);
 
 	present = (gpio_result == GPIO_RESULT_OK) && !clock_pin;
 
-- 
2.19.1