gpu: nova-core: gsp: clarify comments about invariants and pointer roles

Disambiguate a few things in comments in cmdq.rs.

Signed-off-by: Eliot Courtney <ecourtney@nvidia.com>
Reviewed-by: Gary Guo <gary@garyguo.net>
Link: https://patch.msgid.link/20260129-nova-core-cmdq1-v3-2-2ede85493a27@nvidia.com
Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>

diff --git a/drivers/gpu/nova-core/gsp/cmdq.rs b/drivers/gpu/nova-core/gsp/cmdq.rs
index f139aad7af3fdc5f0899c6466bc477325c1cc0b4..0743597779f11a03e78cd70ac248d4ecccd90112 100644 (file)
--- a/drivers/gpu/nova-core/gsp/cmdq.rs
+++ b/drivers/gpu/nova-core/gsp/cmdq.rs
@@ -161,12 +161,14 @@ struct GspMem {
     /// Self-mapping page table entries.
     ptes: PteArray<{ GSP_PAGE_SIZE / size_of::<u64>() }>,
     /// CPU queue: the driver writes commands here, and the GSP reads them. It also contains the
-    /// write and read pointers that the CPU updates.
+    /// write and read pointers that the CPU updates. This means that the read pointer here is an
+    /// index into the GSP queue.
     ///
     /// This member is read-only for the GSP.
     cpuq: Msgq,
     /// GSP queue: the GSP writes messages here, and the driver reads them. It also contains the
-    /// write and read pointers that the GSP updates.
+    /// write and read pointers that the GSP updates. This means that the read pointer here is an
+    /// index into the CPU queue.
     ///
     /// This member is read-only for the driver.
     gspq: Msgq,
@@ -222,7 +224,7 @@ impl DmaGspMem {
         // - We will only access the driver-owned part of the shared memory.
         // - Per the safety statement of the function, no concurrent access will be performed.
         let gsp_mem = &mut unsafe { self.0.as_slice_mut(0, 1) }.unwrap()[0];
-        // PANIC: per the invariant of `cpu_write_ptr`, `tx` is `<= MSGQ_NUM_PAGES`.
+        // PANIC: per the invariant of `cpu_write_ptr`, `tx` is `< MSGQ_NUM_PAGES`.
         let (before_tx, after_tx) = gsp_mem.cpuq.msgq.data.split_at_mut(tx);
 
         if rx <= tx {
@@ -257,7 +259,7 @@ impl DmaGspMem {
         // - We will only access the driver-owned part of the shared memory.
         // - Per the safety statement of the function, no concurrent access will be performed.
         let gsp_mem = &unsafe { self.0.as_slice(0, 1) }.unwrap()[0];
-        // PANIC: per the invariant of `cpu_read_ptr`, `xx` is `<= MSGQ_NUM_PAGES`.
+        // PANIC: per the invariant of `cpu_read_ptr`, `rx` is `< MSGQ_NUM_PAGES`.
         let (before_rx, after_rx) = gsp_mem.gspq.msgq.data.split_at(rx);
 
         match tx.cmp(&rx) {
@@ -315,7 +317,7 @@ impl DmaGspMem {
     //
     // # Invariants
     //
-    // - The returned value is between `0` and `MSGQ_NUM_PAGES`.
+    // - The returned value is within `0..MSGQ_NUM_PAGES`.
     fn gsp_write_ptr(&self) -> u32 {
         let gsp_mem = self.0.start_ptr();
 
@@ -329,7 +331,7 @@ impl DmaGspMem {
     //
     // # Invariants
     //
-    // - The returned value is between `0` and `MSGQ_NUM_PAGES`.
+    // - The returned value is within `0..MSGQ_NUM_PAGES`.
     fn gsp_read_ptr(&self) -> u32 {
         let gsp_mem = self.0.start_ptr();
 
@@ -343,7 +345,7 @@ impl DmaGspMem {
     //
     // # Invariants
     //
-    // - The returned value is between `0` and `MSGQ_NUM_PAGES`.
+    // - The returned value is within `0..MSGQ_NUM_PAGES`.
     fn cpu_read_ptr(&self) -> u32 {
         let gsp_mem = self.0.start_ptr();
 
@@ -372,7 +374,7 @@ impl DmaGspMem {
     //
     // # Invariants
     //
-    // - The returned value is between `0` and `MSGQ_NUM_PAGES`.
+    // - The returned value is within `0..MSGQ_NUM_PAGES`.
     fn cpu_write_ptr(&self) -> u32 {
         let gsp_mem = self.0.start_ptr();