From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 790653FC3 for ; Sat, 11 Sep 2021 11:56:11 +0000 (UTC) Received: by mail.kernel.org (Postfix) with ESMTPSA id 42D0F611F0; Sat, 11 Sep 2021 11:56:10 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1631361370; bh=lGmgTFSbG/Gs9rf2FxKe3GG+QgffwmnxvoctnWxBkSU=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=oB5WBiiNonBBZGsNVxgo4N7rahKgzeSZz+0DCcOUqo3s11ypdJS09AMk+uJh6Wh3L cbdHirmyPp/EbQoe8rbIT27/P6lHyzXSYLR4T+KdLgKwbh9zEVo2LZdWHDW69pSSs/ awBUsNUvYuqrj8knGWtm+RXO27LkmTULlhim1ruU= Date: Sat, 11 Sep 2021 13:56:08 +0200 From: Greg Kroah-Hartman To: Ojaswin Mujoo 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: References: <20210907115045.2206083-1-gregkh@linuxfoundation.org> <20210910114004.GA23656@ojas> <20210911112911.GA17777@ojas> Precedence: bulk X-Mailing-List: linux-staging@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210911112911.GA17777@ojas> 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? thanks, greg k-h