Instead of silently giving up when all link-training fallback values are
exhausted, this patch modifies the fallback's failure branch to reduces
both max_link_lane_count and max_link_rate to zero (0) and continues to
emit uevents until userspace stops attempting to modeset.
By doing so, we ensure the failing connector, which is in
link-status=Bad, has all its modes pruned (due to effectively having a
bandwidth of 0Gbps).
It is then the userspace's responsibility to ignore connectors with no
modes, even if they are marked as connected.
Signed-off-by: Gil Dekel <gildekel@xxxxxxxxxxxx>
---
drivers/gpu/drm/i915/display/intel_dp.c | 18 ++++++++++++++++--
1 file changed, 16 insertions(+), 2 deletions(-)
diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
index 7067ee3a4bd3..2152ddbab557 100644
--- a/drivers/gpu/drm/i915/display/intel_dp.c
+++ b/drivers/gpu/drm/i915/display/intel_dp.c
@@ -276,8 +276,12 @@ static int intel_dp_common_len_rate_limit(const struct intel_dp *intel_dp,
static int intel_dp_common_rate(struct intel_dp *intel_dp, int index)
{
+ /* This occurs when max link rate drops to 0 via link training fallback*/
+ if (index < 0)
+ return 0;
+
if (drm_WARN_ON(&dp_to_i915(intel_dp)->drm,
- index < 0 || index >= intel_dp->num_common_rates))
+ index >= intel_dp->num_common_rates))
return 162000;
return intel_dp->common_rates[index];
@@ -318,6 +322,9 @@ static int intel_dp_max_common_lane_count(struct intel_dp *intel_dp)
int intel_dp_max_lane_count(struct intel_dp *intel_dp)
{
switch (intel_dp->max_link_lane_count) {
+ /* This occurs when max link lane count drops to 0 via link training fallback*/
+ case 0:
+ return 0;
case 1:
case 2:
case 4:
@@ -672,7 +679,14 @@ int intel_dp_get_link_train_fallback_values(struct intel_dp *intel_dp,
intel_dp->max_link_lane_count = lane_count >> 1;
} else {
drm_err(&i915->drm, "Link Training Unsuccessful\n");
- return -1;
+ /*
+ * Ensure all of the connector's modes are pruned in the next
+ * probe by effectively reducing its bandwidth to 0 so userspace
+ * can ignore it within the next modeset attempt.
+ */
+ intel_dp->max_link_rate = 0;
+ intel_dp->max_link_lane_count = 0;
+ return 0;
}
return 0;
--
Gil Dekel, Software Engineer, Google / ChromeOS Display and Graphics
