From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pf1-f182.google.com (mail-pf1-f182.google.com [209.85.210.182]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id C7A203FC3 for ; Sat, 11 Sep 2021 11:29:18 +0000 (UTC) Received: by mail-pf1-f182.google.com with SMTP id j16so4350229pfc.2 for ; Sat, 11 Sep 2021 04:29:18 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=nE6Vpn2ifraVOUHXGmEpuLZh+Ikao8iz2hSDRjcDdNI=; b=VX+XTfVBN4HIOzLzKYjvnziCEiqpZ5gaTBn+PaJkv34akMtiFiEAIYt2k+7sKh3piV iMcdTCd6WKHuA5iAVDwRngLZIoXugdar1femUuyIpYC1f7RKlsbNJyesm2s2IMzFNPTC yBVwYf9nnATqvbo9UUQPGz/7C5G0fJJtsJPNn49zH895MtXqboiZTGhMHq7scP19wLVW 4wQOT4a1ykOdBGVOsr1uqRLEABMfI3jEDtkqBf6bK9Ij15jHnFQAYDzUCWylRB5OZyOb iLIOBILDRlQHw7+jutgjHbDKStgcMV0wuLzUzIIkO9XVOww8QiGGJLWZ2yPPhFYlxC6x I71g== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=nE6Vpn2ifraVOUHXGmEpuLZh+Ikao8iz2hSDRjcDdNI=; b=OsERVFtZegQKB/PHDqUnJ1kXrl5H4Qlrslk7Mx/AAu1facXiakvpjqCDDRM4r2wP5P WuuXZAqCjALsoYDYtRmAtLXOOff3r21b/FSegQJ1RdRnfB+Iz2uohN9QComcknvuXvap Hr3l3zz5rbDXNH79eYRIAqrs8+RtWsacSZ2pC0BGFm6UQh5x16NBHknDqkBLR46YB3Jw znQdwNyRXj1WlJxtIzhxr0kNuudht7Aepq7lOxt5CEZw1I+RRUdtmMwgIA2uk+6TWIsu 4fuKL2f1Ej1SLukSIad1pK/GbZoB/jh4IHfqEKJC8s8poXDIYclKeDn815FY5qSzisDr ZweQ== X-Gm-Message-State: AOAM532k8a25wykB6MgV6MbkWETulX+sRSSWDt3gHIZANChzW5+NWn1L +BirR9+XmNldizU5k7h7u5A= X-Google-Smtp-Source: ABdhPJz3FdAEaCj7tJJNY31BmDCvgnxcHybUr0YzUiI9N/Qa0F32mc6/ynsC5sQX9aV6iya0MEwBIg== X-Received: by 2002:a63:1309:: with SMTP id i9mr2179080pgl.192.1631359758380; Sat, 11 Sep 2021 04:29:18 -0700 (PDT) Received: from ojas ([122.161.51.62]) by smtp.gmail.com with ESMTPSA id m21sm1570271pjl.14.2021.09.11.04.29.14 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 11 Sep 2021 04:29:18 -0700 (PDT) Date: Sat, 11 Sep 2021 16:59:11 +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: <20210911112911.GA17777@ojas> References: <20210907115045.2206083-1-gregkh@linuxfoundation.org> <20210910114004.GA23656@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: 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. Regards, Ojaswin > > thanks, > > greg k-h