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 > > <panto@xxxxxxxxxxxxxxxxxxxxxxx> 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 > >> <ID>: <SIZE> bytes <part-number>:<version> > >> > >> <ID> is the id of the overlay > >> <SIZE> is the size of the overlay in bytes > >> <part-number>, <version> are (optional) root level properties of the DTBO > >> > >> You can remove an overlay by echoing the <ID> 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@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
