linux-kernel - Re: [PATCH v6 4/4] Documentation: ABI: /sys/firmware/devicetree/overlays

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Date:	Tue, 20 Oct 2015 17:00:13 -0500
From:	Rob Herring <robherring2@...il.com>
To:	Pantelis Antoniou <pantelis.antoniou@...sulko.com>
Cc:	Frank Rowand <frowand.list@...il.com>,
	Matt Porter <mporter@...sulko.com>,
	Koen Kooi <koen@...inion.thruhere.net>,
	Guenter Roeck <linux@...ck-us.net>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-api@...r.kernel.org" <linux-api@...r.kernel.org>
Subject: Re: [PATCH v6 4/4] Documentation: ABI: /sys/firmware/devicetree/overlays

On Tue, Oct 20, 2015 at 4:02 PM, Pantelis Antoniou
<pantelis.antoniou@...sulko.com> wrote:
> Hi Rob,
>
>> On Oct 20, 2015, at 23:56 , Rob Herring <robherring2@...il.com> wrote:
>>
>> On Tue, Oct 20, 2015 at 2:13 PM, Pantelis Antoniou
>> <pantelis.antoniou@...sulko.com> wrote:
>>> Documentation ABI entry for overlays sysfs entries.
>>>
>>> Signed-off-by: Pantelis Antoniou <pantelis.antoniou@...sulko.com>
>>> ---
>>> .../ABI/testing/sysfs-firmware-devicetree-overlays | 40 ++++++++++++++++++++++
>>> 1 file changed, 40 insertions(+)
>>> create mode 100644 Documentation/ABI/testing/sysfs-firmware-devicetree-overlays
>>>
>>> diff --git a/Documentation/ABI/testing/sysfs-firmware-devicetree-overlays b/Documentation/ABI/testing/sysfs-firmware-devicetree-overlays
>>> new file mode 100644
>>> index 0000000..adc4068
>>> --- /dev/null
>>> +++ b/Documentation/ABI/testing/sysfs-firmware-devicetree-overlays
>>> @@ -0,0 +1,40 @@
>>> +What:          /sys/firmware/devicetree/overlays/
>>> +Date:          October 2015
>>> +Contact:       Pantelis Antoniou <pantelis.antoniou@...sulko.com>
>>> +Description:
>>> +               This directory contains the applied device tree overlays of
>>> +               the running system, as directories of the overlay id.
>>> +
>>> +               enable: The master enable switch, by default is 1, and when
>>> +                       set to 0 it cannot be re-enabled for security reasons.
>>> +
>>> +               The discussion about this switch takes place in:
>>> +               http://comments.gmane.org/gmane.linux.drivers.devicetree/101871
>>> +
>>> +               Kees Cook:
>>> +               "Coming from the perspective of drawing a bright line between
>>> +               kernel and the root user (which tends to start with disabling
>>> +               kernel module loading), I would say that there at least needs
>>> +               to be a high-level one-way "off" switch for the interface so
>>> +               that systems that have this interface can choose to turn it off
>>> +               during initial boot, etc."
>>> +
>>> +What:          /sys/firmware/devicetree/overlays/<id>
>>> +Date:          October 2015
>>> +Contact:       Pantelis Antoniou <pantelis.antoniou@...sulko.com>
>>> +Description:
>>> +               Each directory represents an applied overlay, containing
>>> +               the following attribute files.
>>> +
>>> +               can_remove: The attribute set to 1 means that the overlay can
>>> +                           be removed, while 0 means that the overlay is being
>>> +                           overlapped therefore removal is prohibited.
>>> +
>>> +What:          /sys/firmware/devicetree/overlays/<id>/<fragment-name>/
>>> +Date:          October 2015
>>> +Contact:       Pantelis Antoniou <pantelis.antoniou@...sulko.com>
>>> +Description:
>>> +               Each of these directories contain information about of the
>>> +               particular overlay fragment.
>>> +
>>> +               target: The full-path of the target of the fragment
>>> --
>>
>> What happened to attributes within the fragment dir?
>>
>
> There’s a single attribute named target that contains the target of the fragment.
>
> At the moment this is the only attribute. I eventually intent to put the full contents of the overlay fragment
> there as /sysfs/firmware/devicetree/base does, but this would make things quite complicated for now.
>
> Should I add a What: line for that too?

There should be an entry for every file. These should not be in the
description. So "enable" and "can_remove" need entries too.

Rob
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