On Tue, Jul 16, 2024 at 11:13:24PM +0100, Bryan O'Donoghue wrote:
The use_count check was introduced so that multiple concurrent Raw Data Interfaces RDIs could be driven by different virtual channels VCs on the CSIPHY input driving the video pipeline.
This is an invalid use of use_count though as use_count pertains to the number of times a video entity has been opened by user-space not the number of active streams.
If use_count and stream-on count don't agree then stop_streaming() will break as is currently the case and has become apparent when using CAMSS with libcamera's released softisp 0.3.
The use of use_count like this is a bit hacky and right now breaks regular usage of CAMSS for a single stream case. As an example the "qcam" application in libcamera will fail with an -EBUSY result on stream stop and cannot then subsequently be restarted.
No, stopping qcam results in the splat below, and then it cannot be started again and any attempts to do so fails with -EBUSY.
The kernel log for this fault looks like this:
[ 1265.509831] WARNING: CPU: 5 PID: 919 at drivers/media/common/videobuf2/videobuf2-core.c:2183 __vb2_queue_cancel+0x230/0x2c8 [videobuf2_common] ... [ 1265.510630] Call trace: [ 1265.510636] __vb2_queue_cancel+0x230/0x2c8 [videobuf2_common] [ 1265.510648] vb2_core_streamoff+0x24/0xcc [videobuf2_common] [ 1265.510660] vb2_ioctl_streamoff+0x5c/0xa8 [videobuf2_v4l2] [ 1265.510673] v4l_streamoff+0x24/0x30 [videodev] [ 1265.510707] __video_do_ioctl+0x190/0x3f4 [videodev] [ 1265.510732] video_usercopy+0x304/0x8c4 [videodev] [ 1265.510757] video_ioctl2+0x18/0x34 [videodev] [ 1265.510782] v4l2_ioctl+0x40/0x60 [videodev] ... [ 1265.510944] videobuf2_common: driver bug: stop_streaming operation is leaving buffer 0 in active state [ 1265.511175] videobuf2_common: driver bug: stop_streaming operation is leaving buffer 1 in active state [ 1265.511398] videobuf2_common: driver bug: stop_streaming operation is leaving buffer 2 in active st
Johan