linux-kernel - [PATCH] gpu: nova-core: fix aux device registration for multi-GPU systems

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Message-ID: <20260205041120.127106-1-jhubbard@nvidia.com>
Date: Wed,  4 Feb 2026 20:11:20 -0800
From: John Hubbard <jhubbard@...dia.com>
To: Danilo Krummrich <dakr@...nel.org>,
	Alexandre Courbot <acourbot@...dia.com>
Cc: Joel Fernandes <joelagnelf@...dia.com>,
	Timur Tabi <ttabi@...dia.com>,
	Alistair Popple <apopple@...dia.com>,
	Eliot Courtney <ecourtney@...dia.com>,
	Zhi Wang <zhiw@...dia.com>,
	David Airlie <airlied@...il.com>,
	Simona Vetter <simona@...ll.ch>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	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,
	rust-for-linux@...r.kernel.org,
	LKML <linux-kernel@...r.kernel.org>,
	John Hubbard <jhubbard@...dia.com>
Subject: [PATCH] gpu: nova-core: fix aux device registration for multi-GPU systems

The auxiliary device registration was using a hardcoded ID of 0, which
caused probe() to fail on multi-GPU systems with:

   sysfs: cannot create duplicate filename '/bus/auxiliary/devices/NovaCore.nova-drm.0'

Fix this by using an atomic counter to generate unique IDs for each
GPU's aux device registration. The TODO item to eventually use XArray
for recycling aux device IDs is retained, but for now, this works very
nicely.

This has the side effect of making debugfs[1] work on multi-GPU systems.

[1] https://lore.kernel.org/20260203224757.871729-1-ttabi@nvidia.com

Signed-off-by: John Hubbard <jhubbard@...dia.com>
---
 drivers/gpu/nova-core/driver.rs | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

Hi,

This is based on today's (Feb 4, 2026) linux-next/master branch.

thanks,
John Hubbard

diff --git a/drivers/gpu/nova-core/driver.rs b/drivers/gpu/nova-core/driver.rs
index 5a4cc047bcfc..a542ec0b40fa 100644
--- a/drivers/gpu/nova-core/driver.rs
+++ b/drivers/gpu/nova-core/driver.rs
@@ -1,5 +1,7 @@
 // SPDX-License-Identifier: GPL-2.0
 
+use core::sync::atomic::{AtomicU32, Ordering};
+
 use kernel::{
     auxiliary,
     device::Core,
@@ -19,6 +21,9 @@
 
 use crate::gpu::Gpu;
 
+/// Counter for generating unique auxiliary device IDs.
+static AUXILIARY_ID_COUNTER: AtomicU32 = AtomicU32::new(0);
+
 #[pin_data]
 pub(crate) struct NovaCore {
     #[pin]
@@ -85,12 +90,17 @@ fn probe(pdev: &pci::Device<Core>, _info: &Self::IdInfo) -> impl PinInit<Self, E
                 GFP_KERNEL,
             )?;
 
+            // TODO[XARR]: Use XArray for proper ID allocation/recycling; for now we use a simple
+            // atomic counter which never recycles IDs. A unique ID is required for multi-GPU
+            // systems; without it, probe() fails for all but the first GPU.
+            let aux_id = AUXILIARY_ID_COUNTER.fetch_add(1, Ordering::Relaxed);
+
             Ok(try_pin_init!(Self {
                 gpu <- Gpu::new(pdev, bar.clone(), bar.access(pdev.as_ref())?),
                 _reg <- auxiliary::Registration::new(
                     pdev.as_ref(),
                     c"nova-drm",
-                    0, // TODO[XARR]: Once it lands, use XArray; for now we don't use the ID.
+                    aux_id,
                     crate::MODULE_NAME
                 ),
             }))

base-commit: 0f8a890c4524d6e4013ff225e70de2aed7e6d726
-- 
2.53.0