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authorLyude Paul <lyude@redhat.com>2019-06-20 17:59:25 -0400
committerLyude Paul <lyude@redhat.com>2019-10-24 14:36:13 -0400
commit12a280c7286857119cf0d88c487f695e3a1c0912 (patch)
treeffe1c12fafcf912e4d35374c2395b686df958f2f /drivers/powercap
parent6f85f73821f6af4de4429ab2f2f7958dbd81cb90 (diff)
drm/dp_mst: Add topology ref history tracking for debugging
For very subtle mistakes with topology refs, it can be rather difficult to trace them down with the debugging info that we already have. I had one such issue recently while trying to implement suspend/resume reprobing for MST, and ended up coming up with this. Inspired by Chris Wilson's wakeref tracking for i915, this adds a very similar feature to the DP MST helpers, which allows for partial tracking of topology refs for both ports and branch devices. This is a lot less advanced then wakeref tracking: we merely keep a count of all of the spots where a topology ref has been grabbed or dropped, then dump out that history in chronological order when a port or branch device's topology refcount reaches 0. So far, I've found this incredibly useful for debugging topology refcount errors. Since this has the potential to be somewhat slow and loud, we add an expert kernel config option to enable or disable this feature, CONFIG_DRM_DEBUG_DP_MST_TOPOLOGY_REFS. Changes since v1: * Don't forget to destroy topology_ref_history_lock Changes since v4: * Correct order of kref_put()/topology_ref_history_unlock - we can't unlock the history after kref_put() since the memory might have been freed by that point * Don't print message on allocation error failures, the kernel already does this for us Changes since v5: * Get rid of some leftover usages of %px * Remove a leftover empty return; statement Cc: Juston Li <juston.li@intel.com> Cc: Imre Deak <imre.deak@intel.com> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com> Cc: Harry Wentland <hwentlan@amd.com> Cc: Daniel Vetter <daniel.vetter@ffwll.ch> Reviewed-by: Sean Paul <sean@poorly.run> Signed-off-by: Lyude Paul <lyude@redhat.com> Link: https://patchwork.freedesktop.org/patch/msgid/20191022023641.8026-15-lyude@redhat.com
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