Re: [PATCH v1 0/4] virt: vmgenid: Add devicetree bindings support

From: Rob Herring <robh@kernel.org>
To: David Woodhouse <dwmw2@infradead.org>
Cc: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>,
	Sudan Landge <sudanl@amazon.com>,
	tytso@mit.edu, Jason@zx2c4.com,
	krzysztof.kozlowski+dt@linaro.org, conor+dt@kernel.org,
	sathyanarayanan.kuppuswamy@linux.intel.com,
	thomas.lendacky@amd.com, dan.j.williams@intel.com,
	devicetree@vger.kernel.org, linux-kernel@vger.kernel.org,
	graf@amazon.de, bchalios@amazon.es, xmarcalx@amazon.co.uk,
	ardb@kernel.org, benh <benh@kernel.crashing.org>
Subject: Re: [PATCH v1 0/4] virt: vmgenid: Add devicetree bindings support
Date: Thu, 21 Mar 2024 08:32:50 -0500	[thread overview]
Message-ID: <20240321133250.GA1600070-robh@kernel.org> (raw)
In-Reply-To: <60404403932a984d1f75d111ff53b9053af03579.camel@infradead.org>

On Wed, Mar 20, 2024 at 04:55:45PM +0000, David Woodhouse wrote:
> On Wed, 2024-03-20 at 11:15 -0500, Rob Herring wrote:
> > On Wed, Mar 20, 2024 at 01:50:43PM +0000, David Woodhouse wrote:
> > > On Tue, 2024-03-19 at 16:24 +0100, Krzysztof Kozlowski wrote:
> > > > On 19/03/2024 15:32, Sudan Landge wrote:
> > > > > This small series of patches aims to add devicetree bindings support for
> > > > > the Virtual Machine Generation ID (vmgenid) driver.
> > > > > 
> > > > > Virtual Machine Generation ID driver was introduced in commit af6b54e2b5ba
> > > > > ("virt: vmgenid: notify RNG of VM fork and supply generation ID") as an
> > > > > ACPI only device.
> > > > > We would like to extend vmgenid to support devicetree bindings because:
> > > > > 1. A device should not be defined as an ACPI or DT only device.
> > 
> > This (and the binding patch) tells me nothing about what "Virtual 
> > Machine Generation ID driver" is and isn't really justification for 
> > "why".
> 
> It's a reference to a memory area which the OS can use to tell whether
> it's been snapshotted and restored (or 'forked'). A future submission
> should have a reference to something like
> https://www.qemu.org/docs/master/specs/vmgenid.html or the Microsoft
> doc which is linked from there.

That doc mentions fw_cfg for which we already have a binding. Why can't 
it be used/extended here?

Rob

[1] https://www.kernel.org/doc/Documentation/devicetree/bindings/firmware/qemu%2Cfw-cfg-mmio.yaml