Re: [PATCH 3/3] DT: proc: Add runtime overlay interface in /proc

From: Ionut Nicu
Date: Wed Nov 06 2013 - 04:52:41 EST


On 05.11.2013 19:41, ext 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
> /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
> 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

Wouldn't it be easier if echo "-BB-UART2-00A0" > device-tree-overlay-status was
supported also? That way one doesn't need to know the order in which the
overlays were applied or parse the status file to get the <ID>.

> Removes the overlay.
> Note that this seldom works on most platforms since platform_device
> removal is something that almost never works without extra patches.
> Signed-off-by: Pantelis Antoniou <panto@xxxxxxxxxxxxxxxxxxxxxxx>

It would be very helpful to me if I would have a notification mechanism
for overlay add and remove operations based on blocking_notifier_call_chain(),.
This way other drivers can be notified when the dt changes.

But I guess that could be added in the future with another patch.

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