Re: [PATCH RFC 1/2] dt-bindings: mtd: ubi-volume: add 'volume-is-critical' property

From: Daniel Golle <daniel@makrotopia.org>
To: Krzysztof Kozlowski <krzk@kernel.org>
Cc: Miquel Raynal <miquel.raynal@bootlin.com>,
	Richard Weinberger <richard@nod.at>,
	Vignesh Raghavendra <vigneshr@ti.com>,
	Rob Herring <robh@kernel.org>,
	Krzysztof Kozlowski <krzk+dt@kernel.org>,
	Conor Dooley <conor+dt@kernel.org>,
	Zhihao Cheng <chengzhihao1@huawei.com>,
	John Crispin <john@phrozen.org>,
	linux-mtd@lists.infradead.org, devicetree@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH RFC 1/2] dt-bindings: mtd: ubi-volume: add 'volume-is-critical' property
Date: Sat, 28 Sep 2024 14:09:07 +0100	[thread overview]
Message-ID: <Zvf_84xxhxwpPgee@makrotopia.org> (raw)
In-Reply-To: <7a2e8819-ac70-4070-a731-53994c72cd79@kernel.org>

On Sat, Sep 28, 2024 at 03:02:47PM +0200, Krzysztof Kozlowski wrote:
> On 28/09/2024 14:47, Daniel Golle wrote:
> > Add the 'volume-is-critical' boolean property which marks a UBI volume
> > as critical for the device to boot. If set it prevents the user from
> > all kinds of write access to the volume as well as from renaming it or
> > detaching the UBI device it is located on.
> > 
> > Signed-off-by: Daniel Golle <daniel@makrotopia.org>
> > ---
> >  .../devicetree/bindings/mtd/partitions/ubi-volume.yaml   | 9 +++++++++
> >  1 file changed, 9 insertions(+)
> > 
> > diff --git a/Documentation/devicetree/bindings/mtd/partitions/ubi-volume.yaml b/Documentation/devicetree/bindings/mtd/partitions/ubi-volume.yaml
> > index 19736b26056b..2bd751bb7f9e 100644
> > --- a/Documentation/devicetree/bindings/mtd/partitions/ubi-volume.yaml
> > +++ b/Documentation/devicetree/bindings/mtd/partitions/ubi-volume.yaml
> > @@ -29,6 +29,15 @@ properties:
> >      description:
> >        This container may reference an NVMEM layout parser.
> >  
> > +  volume-is-critical:
> > +    description: This parameter, if present, indicates that the UBI volume
> > +      contains early-boot firmware images or data which should not be clobbered.
> > +      If set, it prevents the user from renaming the volume, writing to it or
> > +      making any changes affecting it, as well as detaching the UBI device it is
> > +      located on, so direct access to the underlying MTD device is prevented as
> > +      well.
> > +    type: boolean
> 
> UBI volumes are mapping to partitions 1-to-1, right? So rather I would
> propose to use partition.yaml - we already have read-only there with
> very similar description.

No, that's not the case.

An MTD partition can be used as UBI device. A UBI device (and hence MTD
partition) can host *several* UBI volumes.

Marking the MTD partition as 'read-only' won't work, as UBI needs
read-write access to perform bad block relocation, scrubbing, ...

Also, typically not all UBI volumes on a UBI device are
read-only/critical but only a subset of them.

But you are right that the description is inspired by the description
of the 'read-only' property in partition.yaml ;)

I initially thought to also name the property 'read-only', just like
for MTD partitions. However, as the desired effect goes beyond
preventing write access to the volume itself, I thought it'd be
better to use a new name.

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