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According to the specification[1] the 'capabilities' describe the physical device as a whole and the 'device_caps' describe the current device node. The existence of 'device_caps' is indicated by the V4L2_CAP_DEVICE_CAPS capability flag. Use the 'device_caps' if available to generate the correct ID_V4L_CAPABILITIES for the current device node. This is relevant for UVC devices with current kernels: Two /dev/videoX devices exist for those. One for video and one for metadata. The V4L2_CAP_VIDEO_CAPTURE flag is present in the 'capabilities' for both device nodes but only in the 'device_caps' of the video device node. Without this, the ID_V4L_CAPABILITIES of the metadata device node incorrectly contains 'capture'. [1] https://www.linuxtv.org/downloads/v4l-dvb-apis-new/uapi/v4l/vidioc-querycap.html systemd-commit: 646876105fe1799355715839477958adf1d096fd Author: Michael Olbrich <m.olbrich@pengutronix.de> Date: Sun Feb 3 10:52:02 2019 +0100
kaniini
approved these changes
Oct 16, 2021
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Author: Michael Olbrich m.olbrich@pengutronix.de
Date: Sun Feb 3 10:52:02 2019 +0100
v4l_id: use device_caps if available
According to the specification[1] the 'capabilities' describe the physical
device as a whole and the 'device_caps' describe the current device node.
The existence of 'device_caps' is indicated by the V4L2_CAP_DEVICE_CAPS
capability flag.
Use the 'device_caps' if available to generate the correct
ID_V4L_CAPABILITIES for the current device node.
This is relevant for UVC devices with current kernels: Two /dev/videoX
devices exist for those. One for video and one for metadata. The
V4L2_CAP_VIDEO_CAPTURE flag is present in the 'capabilities' for both
device nodes but only in the 'device_caps' of the video device node.
Without this, the ID_V4L_CAPABILITIES of the metadata device node
incorrectly contains 'capture'.
[1] https://www.linuxtv.org/downloads/v4l-dvb-apis-new/uapi/v4l/vidioc-querycap.html
systemd-commit: 646876105fe1799355715839477958adf1d096fd