Hi Matt, On Nov 6, 2013, at 10:16 PM, Matt Porter wrote: > 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. > I see. This can be made to work. > 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. > > Oops... >> /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 > Oh well, let's see what the maintainer have to say about which way to do. Any option of the tree presented would work fine. > -Matt 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
