drm/amd/display: Add retry to read ddc_clock pin
authorPaul Hsieh <paul.hsieh@amd.com>
Thu, 22 Nov 2018 10:43:45 +0000 (18:43 +0800)
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Tue, 12 Feb 2019 18:47:12 +0000 (19:47 +0100)
commit1baca23ade65af672080550aac5da653e53f413c
tree342744928a1e1c3bd8435a44f4d2fffe4d4dc067
parenta756020008e80b30a2b3313666f50b3ae1da9c17
drm/amd/display: Add retry to read ddc_clock pin

[ 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