From d3f36fa57aa289c43e01da16c928a2cd971ad5dc Mon Sep 17 00:00:00 2001
From: John Hubbard <jhubbard@nvidia.com>
Date: Fri, 20 Feb 2026 18:09:15 -0800
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

Reviewed-by: Gary Guo <gary@garyguo.net>
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
Link: https://patch.msgid.link/20260221020952.412352-2-jhubbard@nvidia.com
[ Use LKMM atomics; inline and slightly reword TODO comment. - Danilo ]
Signed-off-by: Danilo Krummrich <dakr@kernel.org>
---
 drivers/gpu/nova-core/driver.rs | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/nova-core/driver.rs b/drivers/gpu/nova-core/driver.rs
index e39885c0d5ca..84b0e1703150 100644
--- a/drivers/gpu/nova-core/driver.rs
+++ b/drivers/gpu/nova-core/driver.rs
@@ -14,11 +14,20 @@
     },
     prelude::*,
     sizes::SZ_16M,
-    sync::Arc, //
+    sync::{
+        atomic::{
+            Atomic,
+            Relaxed, //
+        },
+        Arc,
+    },
 };
 
 use crate::gpu::Gpu;
 
+/// Counter for generating unique auxiliary device IDs.
+static AUXILIARY_ID_COUNTER: Atomic<u32> = Atomic::new(0);
+
 #[pin_data]
 pub(crate) struct NovaCore {
     #[pin]
@@ -90,7 +99,9 @@ fn probe(pdev: &pci::Device<Core>, _info: &Self::IdInfo) -> impl PinInit<Self, E
                 _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.
+                    // TODO[XARR]: Use XArray or perhaps IDA for proper ID allocation/recycling. For
+                    // now, use a simple atomic counter that never recycles IDs.
+                    AUXILIARY_ID_COUNTER.fetch_add(1, Relaxed),
                     crate::MODULE_NAME
                 ),
             }))