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Subject: Re: [PATCH v4 4/4] Documentation: ABI: /sys/firmware/devicetree/overlays
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From: Pantelis Antoniou <pantelis.antoniou@konsulko.com>
In-Reply-To: <CAL_JsqKm9PtDKaabx22Y8WQRJ+RCxWE9Fj+kO2dCJ7_UzriyzA@mail.gmail.com>
Date: Mon, 15 Jun 2015 16:26:57 +0300
Cc: Grant Likely <grant.likely@secretlab.ca>,
        Andrew Morton <akpm@linux-foundation.org>,
        Matt Porter <mporter@konsulko.com>,
        Koen Kooi <koen@dominion.thruhere.net>,
        Guenter Roeck <linux@roeck-us.net>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        "devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-api@vger.kernel.org" <linux-api@vger.kernel.org>
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To: Rob Herring <robherring2@gmail.com>
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Hi Rob,

> On Jun 15, 2015, at 16:24 , Rob Herring <robherring2@gmail.com> wrote:
> 
> On Fri, Jun 12, 2015 at 2:38 PM, Pantelis Antoniou
> <pantelis.antoniou@konsulko.com> wrote:
>> Documentation ABI entry for overlays sysfs entries.
>> 
>> Signed-off-by: Pantelis Antoniou <pantelis.antoniou@konsulko.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@konsulko.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@konsulko.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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