Hi,
Following the report from Sudip Mukherjee, the previous version of that patch got reverted until a fix was found.
While it's not clear yet why we end up in that situation, the culprit is that the original patch in its ASoC prepare hook was calling the vc4_hdmi_set_n_cts function that in turned relied on the connector->state->crtc pointer being non-NULL.
However, no particular caution was being done to make sure that was the case, eventually leading to a NULL pointer dereference under the "right" circumstances.
We did however had some checks for the pointers sanity in the original patch, but they were only enforced when the device was opened, and we were only checking for the connector->state pointer.
The fix is then two-fold: First, we check that we can actually perform audio operations in both startup and prepare, since the situation could have changed between the time the device was opened and the time when we actually start streaming. Then, the encoder->crtc conversion patch has been changed to check on connector->state->crtc as well in that sanity check to avoid dereferencing it if it's NULL.
Let me know what you think, Maxime
Maxime Ripard (2): drm/vc4: hdmi: Check the device state in prepare() drm/vc4: hdmi: Remove drm_encoder->crtc usage
drivers/gpu/drm/vc4/vc4_hdmi.c | 75 ++++++++++++++++++++++++++-------- 1 file changed, 57 insertions(+), 18 deletions(-)