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V4L2_BUF_TYPE_VIDEO_OUTPUT_MPLANE is a v4l2_buf_type enum value (10), not a capability bit, so OR-ing it into the device_caps mask yielded 0x0000000a instead of 0x00002002. A device advertising only V4L2_CAP_VIDEO_OUTPUT_MPLANE therefore fell through to VFL_DIR_RX instead of VFL_DIR_TX, and the stray 0x8 bit is not part of the V4L2_CAP_* space at all. With the wrong direction, determine_valid_ioctls() in the V4L2 core rejects VIDIOC_ENUMOUTPUT, VIDIOC_G_OUTPUT, VIDIOC_S_OUTPUT and the VIDIOC_*AUDOUT ioctls with -ENOTTY even though the driver implements them, and instead enables capture-only ioctls such as VIDIOC_ENUMINPUT, VIDIOC_G_INPUT, VIDIOC_S_INPUT and VIDIOC_QUERYSTD. Format negotiation keeps working because the driver registers both the _vid_cap and _vid_out variants of ENUM_FMT/G_FMT/S_FMT/TRY_FMT, which is why the bug went unnoticed. Fixes: f364e65 ("Initial commit")
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V4L2_BUF_TYPE_VIDEO_OUTPUT_MPLANEis av4l2_buf_typeenum value (10), not acapability bit, so OR-ing it into the
device_capsmask yielded the wrong value:V4L2_CAP_VIDEO_OUTPUT (0x2) | 10=0x0000000aV4L2_CAP_VIDEO_OUTPUT (0x2) | V4L2_CAP_VIDEO_OUTPUT_MPLANE (0x2000)=0x00002002A device advertising only
V4L2_CAP_VIDEO_OUTPUT_MPLANEtherefore fell through toVFL_DIR_RXinstead ofVFL_DIR_TX. The stray0x8bit that the old mask picked upis not part of the
V4L2_CAP_*space at all.Impact
vfl_dirfeedsdetermine_valid_ioctls()in the V4L2 core, whereis_rx = vfl_dir != VFL_DIR_TXandis_tx = vfl_dir != VFL_DIR_RX. With the directionmisdetected, an mplane-only output device:
-ENOTTYforVIDIOC_ENUMOUTPUT,VIDIOC_G_OUTPUT,VIDIOC_S_OUTPUTand theVIDIOC_*AUDOUTioctls, even though the driver implements all of themVIDIOC_ENUMINPUT,VIDIOC_G_INPUT,VIDIOC_S_INPUT,VIDIOC_QUERYSTD,VIDIOC_G_TUNERand friendsFormat negotiation keeps working either way, because the driver registers both the
_vid_capand_vid_outvariants ofENUM_FMT/G_FMT/S_FMT/TRY_FMT. That islikely why this went unnoticed;
v4l2-compliancewould flag the direction-exclusiveioctls.
Notes
The line dates back to the initial commit. f365fc5 ("driver: properly set device
direction") touched these exact lines to change
vfl_dir |=to=, but the typo oneline below was missed.