From mboxrd@z Thu Jan 1 00:00:00 1970 From: Matt Porter Subject: Re: [PATCH 3/3] DT: proc: Add runtime overlay interface in /proc Date: Wed, 6 Nov 2013 15:16:20 -0500 Message-ID: <20131106201620.GN28156@beef> References: <1383676898-29819-1-git-send-email-panto@antoniou-consulting.com> <1383676898-29819-4-git-send-email-panto@antoniou-consulting.com> <8EBC2D5B-74A4-4A85-8BEE-9EAEBFF045D4@antoniou-consulting.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <8EBC2D5B-74A4-4A85-8BEE-9EAEBFF045D4-wVdstyuyKrO8r51toPun2/C9HSW9iNxf@public.gmane.org> Sender: devicetree-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Pantelis Antoniou Cc: Rob Herring , Grant Likely , Stephen Warren , Koen Kooi , Alison Chaiken , Dinh Nguyen , Jan Lubbe , Alexander Sverdlin , Michael Stickel , Guenter Roeck , Dirk Behme , Alan Tull , Sascha Hauer , Michael Bohan , Ionut Nicu , Michal Simek , Matt Ranostay , "devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , "linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" List-Id: devicetree@vger.kernel.org On Wed, Nov 06, 2013 at 09:24:12PM +0200, Pantelis Antoniou wrote: > Hi Rob, > > On Nov 6, 2013, at 9:10 PM, Rob Herring wrote: > > > On Tue, Nov 5, 2013 at 12:41 PM, Pantelis Antoniou > > wrote: > >> Add a runtime interface to /proc to enable generic device tree overlay > >> usage. > >> > >> Two new /proc files are added: > >> > >> /proc/device-tree-overlay & /proc/device-tree-overlay-status > > > > I think we really want all this to live under sysfs. Grant did patches > > to move /proc/device-tree to /sys, but it never went upstream: > > > > v2: https://lkml.org/lkml/2013/3/21/215 > > v1: https://lkml.org/lkml/2013/3/20/311 > > > > Yes, I'm aware; the location of this control interface in /proc is > unusual, but had to go somewhere. It should be easy enough to move it to > /sys. > > >> /proc/device-tree-overlay accepts a stream of a device tree objects and > >> applies it to the running kernel's device tree. > >> > >> $ cat ~/BB-UART2-00A0.dtbo >device-tree-overlay > >> overlay_proc_release: Applied #2 overlay segments @0 > >> > >> /proc/device-tree-overlay-status displays the the overlays added using > >> the /proc interface > >> > >> $ cat device-tree-overlay-status > >> 0: 861 bytes BB-UART2:00A0 > > > > Is the size useful information? > > > > If the overlay doesn't contain part-number/version properties there is nothing > to differentiate each one loaded. No file information, it is just a byte stream > interface. > > >> > >> The format of the status line is > >> : bytes : > >> > >> is the id of the overlay > >> is the size of the overlay in bytes > >> , are (optional) root level properties of the DTBO > >> > >> You can remove an overlay by echoing the number of the overlay > >> precedded with a '-' > >> > >> So > >> $ echo "-0" >device-tree-overlay-status > >> > >> Removes the overlay. > > > > This interface seems racy. Could the id change on you between reading > > the status and echoing to remove the overlay? > > > > I would rather see a file created for each overlay and simply echo 0 > > or "remove" to remove the overlay. Or possibly it needs to be a > > directory per overlay with several files for info and control. This > > would be more inline with typical sysfs design. > > > > It was suggested to use a configfs interface. IIRC configfs can do what you > propose. > > Something like > > /config/dto/add <- load by cat overlay.dtbo >/config/dto/load In a configfs it makes more sense to mkdir. FWIW, USB gadget configfs is a good example of this. mkdir /config/dto/0 which would cause the kernel to create the attribute under that directory: /config/dto/0/load Which you use to load as noted above. Only problem is that configfs doesn't support binary attributes like sysfs. If it is a agreed that overlays are configuration then that would be a strong argument to bring over the binary attribute feature. > /config/dto/0/remove <- unload by echo 1 >/config/dto/0/remove rmdir /config/dto/0 > /config/dto/0/${prop} <- root level properties that are ignore by the overlay > mechanism -Matt -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html