I got kernel WARNINGs frequently on Haswell laptops complaining about
invalid max DP link bw. With drm.debug=0x0e, it turned out that the
obtained DPCD is utterly bogus when it happens:
[drm:intel_dp_get_dpcd], DPCD: 4d 4d 4d 4d 4d 4d 4d 4d 4d 4d 4d 4d 4d 4d 4d
This seems happening intermittently without plug state changes and
even after the first few reads succeeded. As a workaround, add a
sanity check for such bogus values and retry reading if it hits.
Signed-off-by: Takashi Iwai <ti...@suse.de>
---
drivers/gpu/drm/i915/intel_dp.c | 15 ++++++++++++++-
1 file changed, 14 insertions(+), 1 deletion(-)
diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index eb8139da9763..f596353da557 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -2792,13 +2792,26 @@ intel_dp_get_dpcd(struct intel_dp *intel_dp)
struct intel_digital_port *dig_port = dp_to_dig_port(intel_dp);
struct drm_device *dev = dig_port->base.base.dev;
struct drm_i915_private *dev_priv = dev->dev_private;
-
+ int retry = 0;
char dpcd_hex_dump[sizeof(intel_dp->dpcd) * 3];
+ again:
if (intel_dp_aux_native_read_retry(intel_dp, 0x000, intel_dp->dpcd,
sizeof(intel_dp->dpcd)) == 0)
return false; /* aux transfer failed */
+ /* sanity check: sometimes DPCD contains a series of same bogus value
+ * even though the above returned success. Retry reading in that case.
+ */
+ if (intel_dp->dpcd[0]) {
+ int i;
+ for (i = 1; i < sizeof(intel_dp->dpcd); i++)
+ if (intel_dp->dpcd[i] != intel_dp->dpcd[0])
+ break;
+ if (i >= sizeof(intel_dp->dpcd) && retry++ < 2)
+ goto again;
+ }
+
hex_dump_to_buffer(intel_dp->dpcd, sizeof(intel_dp->dpcd),
32, 1, dpcd_hex_dump, sizeof(dpcd_hex_dump), false);
DRM_DEBUG_KMS("DPCD: %s\n", dpcd_hex_dump);
--
1.8.4.3
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