On Fri Jan 23, 2026 at 12:12 PM GMT, Eliot Courtney wrote:
> Disambiguate a few things in comments in cmdq.rs.
>
> Signed-off-by: Eliot Courtney <[email protected]>
> ---
> drivers/gpu/nova-core/gsp/cmdq.rs | 18 ++++++++++--------
> 1 file changed, 10 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/gpu/nova-core/gsp/cmdq.rs
> b/drivers/gpu/nova-core/gsp/cmdq.rs
> index f139aad7af3f..09c28eeb6f12 100644
> --- 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 @@ 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`.
Can this just be `tx < 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 between `0` and `MSGQ_NUM_PAGES - 1`,
> inclusive.
I wonder if this can be `is within 0..MSGQ_NUM_PAGES`. What do others think?
Best,
Gary
> 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 between `0` and `MSGQ_NUM_PAGES - 1`,
> inclusive.
> 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 between `0` and `MSGQ_NUM_PAGES - 1`,
> inclusive.
> 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 between `0` and `MSGQ_NUM_PAGES - 1`,
> inclusive.
> fn cpu_write_ptr(&self) -> u32 {
> let gsp_mem = self.0.start_ptr();
>
