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>

diff --git a/drivers/gpu/nova-core/driver.rs b/drivers/gpu/nova-core/driver.rs
index e39885c0d5ca5d037da80fa50e01b387970e52fa..84b0e1703150e81e103883dfc6ebce32bab5f83d 100644 (file)
--- a/drivers/gpu/nova-core/driver.rs
+++ b/drivers/gpu/nova-core/driver.rs
@@ -14,11 +14,20 @@ use kernel::{
     },
     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 @@ impl pci::Driver for NovaCore {
                 _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
                 ),
             }))