linux-kernel - Re: [PATCH v4 2/3] gpu: nova-core: avoid probing non-display/compute PCI functions

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Message-Id: <DC7AZL4OWXTY.2F7TRSCZYNK6S@nvidia.com>
Date: Wed, 20 Aug 2025 22:52:50 +0900
From: "Alexandre Courbot" <acourbot@...dia.com>
To: "John Hubbard" <jhubbard@...dia.com>, "Danilo Krummrich"
 <dakr@...nel.org>
Cc: "Joel Fernandes" <joelagnelf@...dia.com>, "Timur Tabi"
 <ttabi@...dia.com>, "Alistair Popple" <apopple@...dia.com>, "David Airlie"
 <airlied@...il.com>, "Simona Vetter" <simona@...ll.ch>, "Bjorn Helgaas"
 <bhelgaas@...gle.com>, Krzysztof Wilczyński
 <kwilczynski@...nel.org>, "Miguel Ojeda" <ojeda@...nel.org>, "Alex Gaynor"
 <alex.gaynor@...il.com>, "Boqun Feng" <boqun.feng@...il.com>, "Gary Guo"
 <gary@...yguo.net>, Björn Roy Baron
 <bjorn3_gh@...tonmail.com>, "Benno Lossin" <lossin@...nel.org>, "Andreas
 Hindborg" <a.hindborg@...nel.org>, "Alice Ryhl" <aliceryhl@...gle.com>,
 "Trevor Gross" <tmgross@...ch.edu>, <nouveau@...ts.freedesktop.org>,
 <linux-pci@...r.kernel.org>, <rust-for-linux@...r.kernel.org>, "LKML"
 <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 2/3] gpu: nova-core: avoid probing
 non-display/compute PCI functions

On Wed Aug 20, 2025 at 12:08 PM JST, John Hubbard wrote:
> NovaCore has so far been too imprecise about figuring out if .probe()
> has found a supported PCI PF (Physical Function). By that I mean:
> .probe() sets up BAR0 (which involves a lot of very careful devres and
> Device<Bound> details behind the scenes). And then if it is dealing with
> a non-supported device such as the .1 audio PF on many GPUs, it fails
> out due to an unexpected BAR0 size. We have been fortunate that the BAR0
> sizes are different.
>
> Really, we should be filtering on PCI class ID instead. These days I
> think we can confidently pick out Nova's supported PF's via PCI class
> ID. And if not, then we'll revisit.
>
> The approach here is to filter on "Display VGA" or "Display 3D", which
> is how PCI class IDs express "this is a modern GPU's PF".
>
> Cc: Danilo Krummrich <dakr@...nel.org>
> Cc: Alexandre Courbot <acourbot@...dia.com>
> Signed-off-by: John Hubbard <jhubbard@...dia.com>
> ---
>  drivers/gpu/nova-core/driver.rs | 28 +++++++++++++++++++++++-----
>  1 file changed, 23 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/gpu/nova-core/driver.rs b/drivers/gpu/nova-core/driver.rs
> index 274989ea1fb4..b60c9defa9d1 100644
> --- a/drivers/gpu/nova-core/driver.rs
> +++ b/drivers/gpu/nova-core/driver.rs
> @@ -1,6 +1,9 @@
>  // SPDX-License-Identifier: GPL-2.0
>  
> -use kernel::{auxiliary, bindings, c_str, device::Core, pci, prelude::*, sizes::SZ_16M, sync::Arc};
> +use kernel::{
> +    auxiliary, bindings, c_str, device::Core, pci, pci::Class, pci::ClassMask, prelude::*,
> +    sizes::SZ_16M, sync::Arc,
> +};
>  
>  use crate::gpu::Gpu;
>  
> @@ -18,10 +21,25 @@ pub(crate) struct NovaCore {
>      PCI_TABLE,
>      MODULE_PCI_TABLE,
>      <NovaCore as pci::Driver>::IdInfo,
> -    [(
> -        pci::DeviceId::from_id(bindings::PCI_VENDOR_ID_NVIDIA, bindings::PCI_ANY_ID as u32),
> -        ()
> -    )]
> +    [
> +        // Modern NVIDIA GPUs will show up as either VGA or 3D controllers.
> +        (
> +            pci::DeviceId::from_class_and_vendor(
> +                Class::DISPLAY_VGA,
> +                ClassMask::ClassSubclass,
> +                bindings::PCI_VENDOR_ID_NVIDIA
> +            ),
> +            ()
> +        ),
> +        (
> +            pci::DeviceId::from_class_and_vendor(
> +                Class::DISPLAY_3D,
> +                ClassMask::ClassSubclass,
> +                bindings::PCI_VENDOR_ID_NVIDIA
> +            ),

This is making use of `from_class_and_vendor`, which is modified in the
next patch, requiring to modify this part of the file again. How about
switching this patch with 3/3 so we only modify the nova-core code once?

I also wonder if we want to merge 1/3 and (the current) 3/3, since 1/3
alone leaves `from_class_and_vendor` into some intermediate state that
nobody will ever get a chance to use anyway, and one doesn't really make
sense without the other. WDYT?