From: Chris Wolfe <cwolfe@xxxxxxxxxxxx>
Unfortunately some combinations of hardware seem to generate successful
communications on the aux channel, which always report deferred. As a
result native_write can wind up in an infinite loop.
This hack adds a large (~10ms) retry limit to avoid a kernel panic,
while hopefully minimizing the impact on working hardware.
Signed-off-by: cwolfe@xxxxxxxxxxxx
BUG=chromium-os:34840
TEST=Manually connect DP to VGA adapter to problem system. Added display
powers up and works normally, rather than black screen and reboot.
Change-Id: Ib1b0001ca8004e65c9c5e353dbdb5e252fd88438
Reviewed-on: https://gerrit.chromium.org/gerrit/34203
Commit-Ready: Chris Wolfe <cwolfe@xxxxxxxxxxxx>
Reviewed-by: Chris Wolfe <cwolfe@xxxxxxxxxxxx>
Tested-by: Chris Wolfe <cwolfe@xxxxxxxxxxxx>
---
drivers/gpu/drm/i915/intel_dp.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)
diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index e5d16bc..ac7d610 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -491,6 +491,7 @@ intel_dp_aux_native_write(struct intel_dp *intel_dp,
uint8_t msg[20];
int msg_bytes;
uint8_t ack;
+ int try;
intel_dp_check_edp(intel_dp);
if (send_bytes > 16)
@@ -501,7 +502,7 @@ intel_dp_aux_native_write(struct intel_dp *intel_dp,
msg[3] = send_bytes - 1;
memcpy(&msg[4], send, send_bytes);
msg_bytes = send_bytes + 4;
- for (;;) {
+ for (try = 0; try < 100; try++) {
ret = intel_dp_aux_ch(intel_dp, msg, msg_bytes, &ack, 1);
if (ret < 0)
return ret;
@@ -512,6 +513,10 @@ intel_dp_aux_native_write(struct intel_dp *intel_dp,
else
return -EIO;
}
+ if (try == 100) {
+ DRM_ERROR("too many retries, giving up\n");
+ return -EREMOTEIO;
+ }
return send_bytes;
}
--
1.8.3.2
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