[PATCH v3 05/31] gpu: nova-core: gsp: decode the FIFO engine table

[Zhi Wang]

From: Alok Kumar <alkumar@xxxxxxxxxx>

GSP_INIT reports the FIFO engine topology used to build the channel map
for vGPU instances.

Decode the count, GMC IDs and flags into GspStaticInfo and expose
host-driven engines in firmware FIFO order, retaining repeated IDs.
Reject counts and indexed entries beyond the driver's 64-entry table
capacity rather than silently accepting a prefix. An omitted count
remains zero.

Cc: Alexandre Courbot <acourbot@xxxxxxxxxx>
Signed-off-by: Alok Kumar <alkumar@xxxxxxxxxx>
Co-developed-by: Zhi Wang <zhiw@xxxxxxxxxx>
Signed-off-by: Zhi Wang <zhiw@xxxxxxxxxx>
---
 drivers/gpu/nova-core/gsp/commands.rs    |  2 +-
 drivers/gpu/nova-core/gsp/fw/commands.rs | 80 ++++++++++++++++++++++++
 2 files changed, 81 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/nova-core/gsp/commands.rs b/drivers/gpu/nova-core/gsp/commands.rs
index 9473004a0921..436ea52689b9 100644
--- a/drivers/gpu/nova-core/gsp/commands.rs
+++ b/drivers/gpu/nova-core/gsp/commands.rs
@@ -126,7 +126,7 @@ pub(crate) fn gsp_init(
 /// # Errors
 ///
 /// - `EINVAL` if the payload is not a whole number of NVKV words, or if the stream is malformed
-///   or omits a required key.
+///   or omits a required key, or the FIFO engine count exceeds the supported table capacity.
 /// - `ENOMEM` if the words or the decoded regions cannot be allocated.
 fn decode_gsp_init_reply(payload_0: &[u8], payload_1: &[u8]) -> Result<GspStaticInfo> {
     const WORD_SIZE: usize = size_of::<u64>();
diff --git a/drivers/gpu/nova-core/gsp/fw/commands.rs b/drivers/gpu/nova-core/gsp/fw/commands.rs
index d0715dca1be2..17ae4224e214 100644
--- a/drivers/gpu/nova-core/gsp/fw/commands.rs
+++ b/drivers/gpu/nova-core/gsp/fw/commands.rs
@@ -29,6 +29,7 @@
     DecoderValue,
     Encodable,
     Encoder,
+    Indexed,
     Key,
     KeyId,
     Required, //
@@ -317,6 +318,52 @@ pub(crate) fn new(
 
 // Decode:
 
+const MAX_FIFO_ENGINES: usize = 64;
+
+/// Bit mask for `NVGMC_SC_ENGINE_FLAGS_IS_HOST_DRIVEN`.
+const ENGINE_FLAGS_IS_HOST_DRIVEN: u32 = 1 << 0;
+
+/// Host-driven GMC engine IDs in hardware FIFO order, including any repeated IDs.
+///
+/// # Invariants
+///
+/// `count` is at most [`MAX_FIFO_ENGINES`]. The first `count` slots are the retained engine IDs.
+#[derive(Copy, Clone)]
+pub(crate) struct FifoEngineList {
+    gmc_ids: [u32; MAX_FIFO_ENGINES],
+    count: usize,
+}
+
+impl FifoEngineList {
+    #[expect(dead_code)]
+    pub(crate) fn gmc_ids(&self) -> &[u32] {
+        // PANIC: The type invariant bounds `count` by the array capacity.
+        &self.gmc_ids[..self.count]
+    }
+}
+
+/// A FIFO engine count that fits the supported tables.
+///
+/// # Invariants
+///
+/// The count is at most [`MAX_FIFO_ENGINES`].
+#[derive(Default)]
+struct FifoEngineCount(usize);
+
+impl TryFrom<DecoderValue<'_>> for FifoEngineCount {
+    type Error = Error;
+
+    fn try_from(value: DecoderValue<'_>) -> Result<Self> {
+        let count = crate::num::u32_as_usize(u32::try_from(value)?);
+        if count > MAX_FIFO_ENGINES {
+            Err(EINVAL)
+        } else {
+            // INVARIANT: The count was checked against the table capacity above.
+            Ok(Self(count))
+        }
+    }
+}
+
 // Should decode with UnknownKeyPolicy::Ignore.
 nvkv_decode! {
     /// Schema for the `GSP_INIT` response.
@@ -326,6 +373,9 @@ pub(crate) struct GspInitResponseSchema => GspStaticInfo {
         fb_regions: Accumulated<FbRegionSchema>,
         bar1_pde_base: Required<u64, { Self::BAR1_PDE_BASE_KEY }>,
         vmmu_segment_size: Key<u64, { Self::VMMU_SEGMENT_SIZE_KEY }>,
+        fifo_engine_count: Key<FifoEngineCount, { Self::FIFO_ENGINE_COUNT_KEY }>,
+        fifo_engine_gmc_ids: Indexed<u32, MAX_FIFO_ENGINES, { Self::FIFO_ENGINE_GMC_ID_KEY }>,
+        fifo_engine_flags: Indexed<u32, MAX_FIFO_ENGINES, { Self::FIFO_ENGINE_FLAGS_KEY }>,
     }
 }
 
@@ -334,6 +384,9 @@ impl GspInitResponseSchema {
     const GPU_NAME_STRING_KEY: KeyId = 0x2000;
     const BAR1_PDE_BASE_KEY: KeyId = 0x1020;
     const VMMU_SEGMENT_SIZE_KEY: KeyId = 0x1050;
+    const FIFO_ENGINE_COUNT_KEY: KeyId = 0x0500;
+    const FIFO_ENGINE_GMC_ID_KEY: KeyId = 0x0501;
+    const FIFO_ENGINE_FLAGS_KEY: KeyId = 0x0502;
 }
 
 /// The static GPU configuration, as decoded from the `GSP_INIT` reply.
@@ -343,6 +396,9 @@ pub(crate) struct GspStaticInfo {
     bar1_pde_base: u64,
     #[cfg_attr(not(CONFIG_KUNIT = "y"), expect(dead_code))]
     vmmu_segment_size: u64,
+    fifo_engine_count: FifoEngineCount,
+    fifo_engine_gmc_ids: [u32; MAX_FIFO_ENGINES],
+    fifo_engine_flags: [u32; MAX_FIFO_ENGINES],
 }
 
 /// Error type for [`GspStaticInfo::gpu_name`].
@@ -407,6 +463,30 @@ pub(crate) fn total_fb_end(&self) -> Option<u64> {
             .checked_add(1)
     }
 
+    /// Returns the host-driven engines in their firmware FIFO order.
+    #[expect(dead_code)]
+    pub(crate) fn fifo_engine_list(&self) -> FifoEngineList {
+        // INVARIANT: The list starts empty and appends at most one ID per supported input slot.
+        let mut fifo_engine_list = FifoEngineList {
+            gmc_ids: [0; MAX_FIFO_ENGINES],
+            count: 0,
+        };
+        for (&gmc_id, &flags) in self
+            .fifo_engine_gmc_ids
+            .iter()
+            .zip(&self.fifo_engine_flags)
+            .take(self.fifo_engine_count.0)
+        {
+            if flags & ENGINE_FLAGS_IS_HOST_DRIVEN != 0 {
+                // PANIC: At most one slot is filled per input, and the input has at most
+                // MAX_FIFO_ENGINES entries, so the next retained ID always fits.
+                fifo_engine_list.gmc_ids[fifo_engine_list.count] = gmc_id;
+                fifo_engine_list.count += 1;
+            }
+        }
+        fifo_engine_list
+    }
+
     /// Returns the BAR1 page directory entry base address.
     pub(crate) fn bar1_pde_base(&self) -> u64 {
         self.bar1_pde_base