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Subject[PATCH 4.19 174/313] drm/amd/display: Add retry to read ddc_clock pin
Date
4.19-stable review patch.  If anyone has any objections, please let me know.

------------------

[ 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 7c89785fd731..23a7ef97afdd 100644
--- a/drivers/gpu/drm/amd/display/dc/core/dc_link.c
+++ b/drivers/gpu/drm/amd/display/dc/core/dc_link.c
@@ -324,7 +324,7 @@ 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 =
@@ -353,11 +353,22 @@ 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


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