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Date:   Wed, 29 Nov 2017 10:11:12 -0600
From:   Alan Tull <atull@...nel.org>
To:     Rob Herring <robh+dt@...nel.org>
Cc:     Frank Rowand <frowand.list@...il.com>,
        Pantelis Antoniou <pantelis.antoniou@...sulko.com>,
        Moritz Fischer <mdf@...nel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        linux-fpga@...r.kernel.org
Subject: Re: [RFC 0/2] of: Add whitelist

On Wed, Nov 29, 2017 at 7:31 AM, Rob Herring <robh+dt@...nel.org> wrote:
> On Wed, Nov 29, 2017 at 3:20 AM, Frank Rowand <frowand.list@...il.com> wrote:
>> On 11/27/17 15:58, Alan Tull wrote:
>>> Here's a proposal for a whitelist to lock down the dynamic device tree.
>>>
>>> For an overlay to be accepted, all of its targets are required to be
>>> on a target node whitelist.
>>>
>>> Currently the only way I have to get on the whitelist is calling a
>>> function to add a node.  That works for fpga regions, but I think
>>> other uses will need a way of having adding specific nodes from the
>>> base device tree, such as by adding a property like 'allow-overlay;'
>>> or 'allow-overlay = "okay";' If that is acceptable, I could use some
>>> advice on where that particular code should go.
>>>
>>> Alan
>>>
>>> Alan Tull (2):
>>>   of: overlay: add whitelist
>>>   fpga: of region: add of-fpga-region to whitelist
>>>
>>>  drivers/fpga/of-fpga-region.c |  9 ++++++
>>>  drivers/of/overlay.c          | 73 +++++++++++++++++++++++++++++++++++++++++++
>>>  include/linux/of.h            | 12 +++++++
>>>  3 files changed, 94 insertions(+)
>>>
>>
>> The plan was to use connectors to restrict where an overlay could be applied.
>> I would prefer not to have multiple methods for accomplishing the same thing
>> unless there is a compelling reason to do so.
>
> Connector nodes need a mechanism to enable themselves, too. I don't
> think connector nodes are going to solve every usecase.
>
> Rob

The two methods I'm suggesting are intended to handle different cases.
  There will exist some drivers that by their nature will want every
instance to be enabled for overlays, such as fpga regions.  The other
case is where drivers could support overlays but that's not the
widespread use for them.  So no need to enable every instance of that
driver for overlays.  In that case the DT property provides some
granularity, only enabling overlays for specific instances of that
driver, leaving the rest of the DT locked down.

If we only want one method, I would choose having the DT property only
and not exporting the functions.  Users would have to add the property
for every FPGA region but that's not really painful.  This would have
the benefit of still keeping the DT locked down unless someone
specifically wanted to enable some regions for overlays for their
particular use.

Alan

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