gpu: nova-core: create GSP-RM logging buffers debugfs entries

Create read-only debugfs entries for LOGINIT, LOGRM, and LOGINTR, which
are the three primary printf logging buffers from GSP-RM.  LOGPMU will
be added at a later date, as it requires support for its RPC message
first.

This patch uses the `pin_init_scope` feature to create the entries.
`pin_init_scope` solves the lifetime issue over the `DEBUGFS_ROOT`
reference by delaying its acquisition until the time the entry is
actually initialized.

Co-developed-by: Alexandre Courbot <acourbot@nvidia.com>
Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
Signed-off-by: Timur Tabi <ttabi@nvidia.com>
Tested-by: John Hubbard <jhubbard@nvidia.com>
Tested-by: Eliot Courtney <ecourtney@nvidia.com>
Link: https://patch.msgid.link/20260319212658.2541610-7-ttabi@nvidia.com
[ Rebase onto Coherent<T> changes. - Danilo ]
Signed-off-by: Danilo Krummrich <dakr@kernel.org>

drivers/gpu/nova-core/gsp.rs

@@ -3,6 +3,7 @@
 mod boot;
 
 use kernel::{
+    debugfs,
     device,
     dma::{
         Coherent,
@@ -106,17 +107,23 @@ fn new(dev: &device::Device<device::Bound>) -> Result<Self> {
     }
 }
 
-/// GSP runtime data.
-#[pin_data]
-pub(crate) struct Gsp {
-    /// Libos arguments.
-    pub(crate) libos: Coherent<[LibosMemoryRegionInitArgument]>,
+struct LogBuffers {
     /// Init log buffer.
     loginit: LogBuffer,
     /// Interrupts log buffer.
     logintr: LogBuffer,
     /// RM log buffer.
     logrm: LogBuffer,
+}
+
+/// GSP runtime data.
+#[pin_data]
+pub(crate) struct Gsp {
+    /// Libos arguments.
+    pub(crate) libos: Coherent<[LibosMemoryRegionInitArgument]>,
+    /// Log buffers, optionally exposed via debugfs.
+    #[pin]
+    logs: debugfs::Scope<LogBuffers>,
     /// Command queue.
     #[pin]
     pub(crate) cmdq: Cmdq,
@@ -130,13 +137,14 @@ pub(crate) fn new(pdev: &pci::Device<device::Bound>) -> impl PinInit<Self, Error
         pin_init::pin_init_scope(move || {
             let dev = pdev.as_ref();
 
+            let loginit = LogBuffer::new(dev)?;
+            let logintr = LogBuffer::new(dev)?;
+            let logrm = LogBuffer::new(dev)?;
+
             // Initialise the logging structures. The OpenRM equivalents are in:
             // _kgspInitLibosLoggingStructures (allocates memory for buffers)
             // kgspSetupLibosInitArgs_IMPL (creates pLibosInitArgs[] array)
             Ok(try_pin_init!(Self {
-                loginit: LogBuffer::new(dev)?,
-                logintr: LogBuffer::new(dev)?,
-                logrm: LogBuffer::new(dev)?,
                 cmdq <- Cmdq::new(dev),
                 rmargs: Coherent::init(dev, GFP_KERNEL, GspArgumentsPadded::new(&cmdq))?,
                 libos: {
@@ -153,6 +161,29 @@ pub(crate) fn new(pdev: &pci::Device<device::Bound>) -> impl PinInit<Self, Error
 
                     libos.into()
                 },
+                logs <- {
+                    let log_buffers = LogBuffers {
+                        loginit,
+                        logintr,
+                        logrm,
+                    };
+
+                    #[allow(static_mut_refs)]
+                    // SAFETY: `DEBUGFS_ROOT` is created before driver registration and cleared
+                    // after driver unregistration, so no probe() can race with its modification.
+                    //
+                    // PANIC: `DEBUGFS_ROOT` cannot be `None` here.  It is set before driver
+                    // registration and cleared after driver unregistration, so it is always
+                    // `Some` for the entire lifetime that probe() can be called.
+                    let log_parent: &debugfs::Dir = unsafe { crate::DEBUGFS_ROOT.as_ref() }
+                        .expect("DEBUGFS_ROOT not initialized");
+
+                    log_parent.scope(log_buffers, dev.name(), |logs, dir| {
+                        dir.read_binary_file(c"loginit", &logs.loginit.0);
+                        dir.read_binary_file(c"logintr", &logs.logintr.0);
+                        dir.read_binary_file(c"logrm", &logs.logrm.0);
+                    })
+                },
             }))
         })
     }