gpu: nova-core: provide a clear error report for unsupported GPUs

Pass in a PCI device to Spec::new(), and provide a Display
implementation for boot42, in order to provide a clear, concise report
of what happened: the driver read NV_PMC_BOOT42, and found that the GPU
is not supported.

For very old GPUs (older than Fermi), the driver still returns ENODEV,
but it does so without a driver-specific dmesg report. That is exactly
appropriate, because if such a GPU is installed, it can only be
supported by Nouveau. And if so, the user is not helped by additional
error messages from Nova.

Here's the full dmesg output for a Blackwell (not yet supported) GPU:

NovaCore 0000:01:00.0: Probe Nova Core GPU driver.
NovaCore 0000:01:00.0: Unsupported chipset: boot42 = 0x1b2a1000 (architecture 0x1b, implementation 0x2)
NovaCore 0000:01:00.0: probe with driver NovaCore failed with error -524

Cc: Alexandre Courbot <acourbot@nvidia.com>
Cc: Danilo Krummrich <dakr@kernel.org>
Cc: Timur Tabi <ttabi@nvidia.com>
Cc: Joel Fernandes <joelagnelf@nvidia.com>
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
[acourbot@nvidia.com: fix commit log with ENODEV (not ENOTSUPP) error
code for unsupported GPUs.]
Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
Message-ID: <20251115010923.1192144-5-jhubbard@nvidia.com>

drivers/gpu/nova-core/gpu.rs

@@ -182,7 +182,7 @@ pub(crate) struct Spec {
 }
 
 impl Spec {
-    fn new(bar: &Bar0) -> Result<Spec> {
+    fn new(dev: &device::Device, bar: &Bar0) -> Result<Spec> {
         // Some brief notes about boot0 and boot42, in chronological order:
         //
         // NV04 through NV50:
@@ -207,7 +207,10 @@ impl Spec {
             return Err(ENODEV);
         }
 
-        Spec::try_from(regs::NV_PMC_BOOT_42::read(bar))
+        let boot42 = regs::NV_PMC_BOOT_42::read(bar);
+        Spec::try_from(boot42).inspect_err(|_| {
+            dev_err!(dev, "Unsupported chipset: {}\n", boot42);
+        })
     }
 }
 
@@ -259,7 +262,7 @@ impl Gpu {
         bar: &'a Bar0,
     ) -> impl PinInit<Self, Error> + 'a {
         try_pin_init!(Self {
-            spec: Spec::new(bar).inspect(|spec| {
+            spec: Spec::new(pdev.as_ref(), bar).inspect(|spec| {
                 dev_info!(pdev.as_ref(),"NVIDIA ({})\n", spec);
             })?,
 

drivers/gpu/nova-core/regs.rs

@@ -67,6 +67,24 @@ impl NV_PMC_BOOT_42 {
             })
             .and_then(Chipset::try_from)
     }
+
+    /// Returns the raw architecture value from the register.
+    fn architecture_raw(self) -> u8 {
+        ((self.0 >> Self::ARCHITECTURE_RANGE.start()) & ((1 << Self::ARCHITECTURE_RANGE.len()) - 1))
+            as u8
+    }
+}
+
+impl kernel::fmt::Display for NV_PMC_BOOT_42 {
+    fn fmt(&self, f: &mut kernel::fmt::Formatter<'_>) -> kernel::fmt::Result {
+        write!(
+            f,
+            "boot42 = 0x{:08x} (architecture 0x{:x}, implementation 0x{:x})",
+            self.0,
+            self.architecture_raw(),
+            self.implementation()
+        )
+    }
 }
 
 // PBUS