Re: [PATCH v3 10/14] gpu: nova-core: bound a GSP wait by a single deadline

[Alexandre Courbot]

On Thu Sep 3, 2026 at 12:15 PM JST, John Hubbard wrote:
<...>
> @@ -611,15 +621,39 @@ pub(crate) fn send_command_no_wait<M>(&self, bar: Bar0<'_>, command: M) -> Resul
>          self.inner.lock().send_command(bar, command)
>      }
>  
> -    /// Receive a message from the GSP.
> +    /// Waits for an unsolicited GSP event of type `M`, logging any other event that arrives
> +    /// first.
> +    ///
> +    /// The queue is locked for the whole wait, for up to [`Self::RECEIVE_TIMEOUT`], so a
> +    /// concurrent command cannot consume the awaited event.
>      ///
> -    /// See [`CmdqInner::receive_msg`] for details.
> -    pub(crate) fn receive_msg<M: MessageFromGsp>(&self, timeout: Delta) -> Result<M>
> +    /// # Errors
> +    ///
> +    /// - `ETIMEDOUT` if the event does not arrive within [`Self::RECEIVE_TIMEOUT`] of the call,
> +    ///   however many other events arrive while waiting.
> +    /// - `EIO` if the queue is poisoned or a message fails framing or checksum validation (see
> +    ///   [`CmdqInner::wait_for_msg`]).

Let's not mention private methods in public documentation.

> +    ///
> +    /// Error codes returned by [`MessageFromGsp::read`] are propagated as-is.
> +    pub(crate) fn await_msg<M: MessageFromGsp>(&self) -> Result<M>
>      where
>          // This allows all error types, including `Infallible`, to be used for `M::InitError`.
>          Error: From<M::InitError>,
>      {
> -        self.inner.lock().receive_msg(timeout)
> +        let mut inner = self.inner.lock();
> +
> +        let deadline = Instant::<Monotonic>::now() + Self::RECEIVE_TIMEOUT;
> +        loop {
> +            let remaining = deadline - Instant::<Monotonic>::now();
> +            if remaining.is_negative() {
> +                break Err(ETIMEDOUT);
> +            }
> +            match inner.receive_msg::<M>(remaining) {
> +                Ok(msg) => break Ok(msg),
> +                Err(ERANGE) => continue,
> +                Err(e) => break Err(e),
> +            }
> +        }

This block and the one from `send_command` are strictly identical - we
should factor them out.

The right place for this seems to be a new method in `CmdqInner`:

    fn await_msg<M: MessageFromGsp>(&mut self) -> Result<M> ...

Then this `await_msg` simply becomes:

    self.inner.lock().await_msg()

While `send_command` is simplified to:

    let mut inner = self.inner.lock();
    inner.send_command(bar, command)?;
    inner.await_msg()