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Sat, 11 Sep 2021 05:51:04 -0700 (PDT) Date: Sat, 11 Sep 2021 18:20:58 +0530 From: Ojaswin Mujoo To: Greg Kroah-Hartman Cc: linux-staging@lists.linux.dev, Nicolas Saenz Julienne , Stefan Wahren , Arnd Bergmann , Dan Carpenter , Phil Elwell , bcm-kernel-feedback-list@broadcom.com, linux-rpi-kernel@lists.infradead.org, linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH] staging: vchiq: convert to use a miscdevice Message-ID: <20210911125058.GA112075@ojas> References: <20210907115045.2206083-1-gregkh@linuxfoundation.org> <20210910114004.GA23656@ojas> <20210911112911.GA17777@ojas> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210911_055106_616537_6998BE1B X-CRM114-Status: GOOD ( 35.68 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Sat, Sep 11, 2021 at 01:56:08PM +0200, Greg Kroah-Hartman wrote: > On Sat, Sep 11, 2021 at 04:59:11PM +0530, Ojaswin Mujoo wrote: > > On Fri, Sep 10, 2021 at 02:05:19PM +0200, Greg Kroah-Hartman wrote: > > > 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. > > Hello, thanks for the explanation and pointers. > > > > The "NAME==vchiq" change doesn't seem to work but I was able to get it > > correctly working by using "KERNEL=vchiq" instead: > > > > KERNEL=="vchiq", GROUP="video", MODE="0660" > > > > I tested this with and without this patch and it works as expected. > > Ah, yes, you are right, I was just guessing, I should have read the udev > documentation :) > > Any chance you can send a patch for this to whatever package that file > comes from? Sure Greg, I can do that. Thanks, ojaswin > > thanks, > > greg k-h _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel