linux-kernel - Re: [PATCH v4 4/4] Documentation: ABI: /sys/firmware/devicetree/overlays

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Message-Id: <B474B6B9-0C7C-4A46-B64F-BD76DA4B7F3B@konsulko.com>
Date:	Mon, 15 Jun 2015 16:26:57 +0300
From:	Pantelis Antoniou <pantelis.antoniou@...sulko.com>
To:	Rob Herring <robherring2@...il.com>
Cc:	Grant Likely <grant.likely@...retlab.ca>,
	Andrew Morton <akpm@...ux-foundation.org>,
	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 v4 4/4] Documentation: ABI: /sys/firmware/devicetree/overlays

Hi Rob,

> On Jun 15, 2015, at 16:24 , Rob Herring <robherring2@...il.com> wrote:
> 
> On Fri, Jun 12, 2015 at 2:38 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 | 35 ++++++++++++++++++++++
>> 1 file changed, 35 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..be2d28b
>> --- /dev/null
>> +++ b/Documentation/ABI/testing/sysfs-firmware-devicetree-overlays
>> @@ -0,0 +1,35 @@
>> +What:          /sys/firmware/devicetree/overlays/
>> +Date:          March 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.
>> +
>> +What:          /sys/firmware/devicetree/overlays/<id>
>> +Date:          March 2015
>> +Contact:       Pantelis Antoniou <pantelis.antoniou@...sulko.com>
>> +Description:
>> +               Each directory represents an applied overlay, containing
>> +               the following attribute files.
>> +
>> +               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."
> 
> Doesn't this below up above with "enable”?

Ugh I guess so.

> 

>> +
>> +               targets: A file containing the list of targets of each overlay
>> +                        with each line containing a target.
> 
> We have OF nodes in sysfs now. Would it be more useful if we created
> links to the target nodes instead of having a list of names?
> 

Probably, this interface is merely informational; things get complicated by
the fact that there can be more than one target in each overlay.

>> +
>> +               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.
>> +
>> --
>> 1.7.12
>> 

Regards

— Pantelis

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