Re: [PATCH v3 12/33] gpu: nova-core: gsp: add GMC dispatch on receive

[Timur Tabi]

On Thu, 2026-09-17 at 18:06 -0700, John Hubbard wrote:
> 
>      /// Waits for an unsolicited GSP event of type `M`. Events that arrive before it are
> logged and
>      /// consumed.
>      ///
> @@ -1097,9 +1110,9 @@ fn payload_slices<'a>(
>      /// # Errors
>      ///
>      /// - `ETIMEDOUT` if no element arrives within `timeout`.
> -    /// - `EIO` if the queue is already poisoned, or if the framing is invalid, which poisons
> it
> -    ///   (see [`Self::poisoned`]).
> -    #[expect(dead_code)]
> +    /// - `EIO` if the queue is already poisoned, or if the framing is invalid, or if the GMC
> API
> +    ///   header and the queue element header declare different payload sizes. Each of these
> +    ///   poisons the queue (see [`Self::poisoned`]).

What does it mean for the size to be "declared"?

>      fn wait_for_element(&self, timeout: Delta) -> Result<QueueElement<'_>> {
>          if self.poisoned.get() {
>              return Err(EIO);
> @@ -1146,8 +1159,89 @@ fn wait_for_element(&self, timeout: Delta) -> Result<QueueElement<'_>>
> {
>              )));
>          };
>  
> +        // GSP-RM writes both sizes from the same payload, so a difference means that one of
> the
> +        // two headers is corrupt, and the driver cannot know which.
> +        if payload_length != num::u32_as_usize(header.gmc.size) {
> +            return Err(self.poison(fmt!(
> +                "GMC seq# {}: GMC API header declares {} payload bytes, element header {}",
> +                header.gmc.sequence,
> +                header.gmc.size,
> +                payload_length
> +            )));

This message doesn't clearly specify what the error is.  How about something like:

"GMC API header declares payload size of {} bytes, but should be {}"