drm/amd/display: Add retry to read ddc_clock pin

[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>

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 9f551fc..912036c 100644 (file)
--- a/drivers/gpu/drm/amd/display/dc/core/dc_link.c
+++ b/drivers/gpu/drm/amd/display/dc/core/dc_link.c
@@ -342,7 +342,7 @@ 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 =
@@ -371,11 +371,22 @@ 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;