On Fri, Sep 10, 2021 at 05:10:04PM +0530, Ojaswin Mujoo wrote: > On Tue, Sep 07, 2021 at 01:50:45PM +0200, Greg Kroah-Hartman wrote: > > Using a struct class, a cdev, and another device just for a single minor > > device is total overkill. Just use a dynamic misc device instead, > > saving lots of logic and memory. > > Hello Greg, > > I got some time to test this out at my end. This seems to work correctly > however there's a small change in permissions applied to /dev/vchiq that > is causing tests to break. > > * Permissions before the patch * > $ ls -l /dev/vchiq > crw-rw---- 1 root video 235, 0 May 7 17:33 vchiq > > * Permissions after the patch * > $ ls -l /dev/vchiq > crw------- 1 root root 10, 125 May 7 17:30 vchiq > > As seen above, after the patch, the cdev is only accessible by root user, > which is causing the tests ($ vchiq_test -f 10) to fail when run as > non-root. Ah, that's not under the kernel's control, but as you point out, it's a udev issue. > I believe assigning the permission and "video" group to /dev/vchiq is > handled by udev, in the downstream pi OS, as seen in this line in > /lib/udev/rules.d/10-local-rpi.rules file: > > SUBSYSTEM=="vchiq", GROUP="video", MODE="0660" > > I'm not completely sure how the SUBSYSTEM part is passed to udev from > the kernel modules, however seems like the miscdevice is not notifying > udev correctly (?). No, the SUBSYSTEM for this device has changed from "vchiq" to "misc". Having a whole subsystem for just one character device is crazy, which is why I did the kernel change. Try changing the line in the udev file to: NAME=="vchiq", GROUP="video", MODE="0660" (SUBSYSTEM changes to NAME) and see if that works both on the newer kernel, and on the older ones as well. thanks, greg k-h
