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

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Message-ID: <20240321133250.GA1600070-robh@kernel.org>
Date: Thu, 21 Mar 2024 08:32:50 -0500
From: Rob Herring <robh@...nel.org>
To: David Woodhouse <dwmw2@...radead.org>
Cc: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
	Sudan Landge <sudanl@...zon.com>, tytso@....edu, Jason@...c4.com,
	krzysztof.kozlowski+dt@...aro.org, conor+dt@...nel.org,
	sathyanarayanan.kuppuswamy@...ux.intel.com, thomas.lendacky@....com,
	dan.j.williams@...el.com, devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org, graf@...zon.de, bchalios@...zon.es,
	xmarcalx@...zon.co.uk, ardb@...nel.org,
	benh <benh@...nel.crashing.org>
Subject: Re: [PATCH v1 0/4] virt: vmgenid: Add devicetree bindings support

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