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 /config/dto/0/remove <- unload by echo 1 >/config/dto/0/remove /config/dto/0/${prop} <- root level properties that are ignore by the overlay mechanism > Rob Regards -- Pantelis -- 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
