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

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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>
This commit is contained in:
Eliot Courtney 2026-01-29 16:45:00 +09:00 committed by Alexandre Courbot
parent 9045ae2afc
commit bbe6831c02
1 changed files with 10 additions and 8 deletions
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18
drivers/gpu/nova-core/gsp/cmdq.rs
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@ -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 @@ fn new(dev: &device::Device<device::Bound>) -> Result<Self> {
// - 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 @@ fn new(dev: &device::Device<device::Bound>) -> Result<Self> {
// - 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 @@ fn allocate_command(&mut self, size: usize) -> Result<GspCommand<'_>> {
//
// # 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 @@ fn gsp_write_ptr(&self) -> u32 {
//
// # 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 @@ fn gsp_read_ptr(&self) -> u32 {
//
// # 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 @@ fn advance_cpu_read_ptr(&mut self, elem_count: u32) {
//
// # 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();