linux-kernel - Re: [PATCH v3 2/2] gpu: nova-core: add boot42 support for next-gen GPUs

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Message-ID: <6ac08d3e-6057-4869-ae41-03a0f900a0bb@kernel.org>
Date: Thu, 30 Oct 2025 15:45:56 +0100
From: Danilo Krummrich <dakr@...nel.org>
To: Timur Tabi <ttabi@...dia.com>
Cc: John Hubbard <jhubbard@...dia.com>, "lossin@...nel.org"
 <lossin@...nel.org>, "a.hindborg@...nel.org" <a.hindborg@...nel.org>,
 "boqun.feng@...il.com" <boqun.feng@...il.com>, Zhi Wang <zhiw@...dia.com>,
 "simona@...ll.ch" <simona@...ll.ch>, "tmgross@...ch.edu"
 <tmgross@...ch.edu>, "alex.gaynor@...il.com" <alex.gaynor@...il.com>,
 "nouveau@...ts.freedesktop.org" <nouveau@...ts.freedesktop.org>,
 "ojeda@...nel.org" <ojeda@...nel.org>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
 "rust-for-linux@...r.kernel.org" <rust-for-linux@...r.kernel.org>,
 "bjorn3_gh@...tonmail.com" <bjorn3_gh@...tonmail.com>,
 Edwin Peer <epeer@...dia.com>, "airlied@...il.com" <airlied@...il.com>,
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 Joel Fernandes <joelagnelf@...dia.com>,
 Alexandre Courbot <acourbot@...dia.com>, "gary@...yguo.net"
 <gary@...yguo.net>, Alistair Popple <apopple@...dia.com>
Subject: Re: [PATCH v3 2/2] gpu: nova-core: add boot42 support for next-gen
 GPUs

On 10/30/25 3:22 PM, Timur Tabi wrote:
> On Wed, 2025-10-29 at 22:30 -0700, John Hubbard wrote:
>> However, I don't want anyone to have to risk reading boot42 on some
>> ancient GPU (earlier than Fermi, even), with uncertain results.
>>
>> And our HW team has promised to leave behind arch0==0, arch1==1 in
>> in boot0, more or less forever, specifically to help us out here.
>>
>> With that in mind, I *do* want to read boot0 for the forseeable future,
>> as a guide to whether to look at boot42. I really think that is the
>> way to thread the needle here.
> 
> Sure, and this is exactly what is_ancient_gpu() does.  It tells you whether to use boot42
> instead of boot0.  It is the only function that looks at boot0.

I think you're indeed talking about the same thing, but thinking differently
about the implementation details.

A standalone is_ancient_gpu() function called from probe() like

	if is_ancient_gpu(bar) {
		return Err(ENODEV);
	}

is what we would probably do in C, but in Rust we should just call

	let spec = Spec::new()?;

from probe() and Spec::new() will return Err(ENODEV) when it run into an ancient
GPU spec internally.