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Message-ID: <38aad6c0e698c8e804694276d1762d61f2068ce8.camel@infradead.org>
Subject: Re:  [PATCH v1 0/4] virt: vmgenid: Add devicetree bindings support
From: David Woodhouse <dwmw2@infradead.org>
To: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>, Sudan Landge
	 <sudanl@amazon.com>, tytso@mit.edu, Jason@zx2c4.com, robh+dt@kernel.org, 
	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
Cc: graf@amazon.de, bchalios@amazon.es, xmarcalx@amazon.co.uk,
 ardb@kernel.org,  benh <benh@kernel.crashing.org>
Date: Wed, 20 Mar 2024 13:50:43 +0000
In-Reply-To: <23692c07-98bd-477d-b244-bba14c50352c@linaro.org>
References: <20240319143253.22317-1-sudanl@amazon.com>
	 <23692c07-98bd-477d-b244-bba14c50352c@linaro.org>
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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 fo=
r
> > the Virtual Machine Generation ID (vmgenid) driver.
> >=20
> > Virtual Machine Generation ID driver was introduced in commit af6b54e2b=
5ba
> > ("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.
>=20
> Virtual stuff is not a device, so your first assumption or rationale is
> not correct.
>=20
> Virtual stuff can be ACPI only, because DT is not for Virtual stuff.

I strongly disagree with this.

Discovering things is what the device-tree is *for*.

We don't want to add extra complexity and overhead on both host and
guest side to make things discoverable in a *less* efficient way.

The device-tree isn't just a last-resort for when we can't possibly do
things differently in a discoverable way. The device-tree is a first-
class citizen and perfectly valid choice as a way to discover things.

We shouldn't be forcing people to turn things into PCI devices just to
avoid adding DT bindings for them.

And we *certainly* shouldn't be directing people towards all the
awfulness of ACPI, and in-kernel bytecode interpreters, and all that
horridness, just because we don't want to use DT to... describe things.


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