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X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: Cx1K9zU3jW8GUiulgZ7IqE8gKXNLr9MLlNmjdtZ6AkCUPx+T9xYMvKPioQLgjPB/GEuSBNY85sG7Vwc0aoBVSQ== X-MS-Exchange-Transport-CrossTenantHeadersStamped: DS6PR12MB600424 On Fri Nov 6, 2026 at 6:08 PM JST, Eliot Courtney wrote: > On Fri Nov 6, 2026 at 4:06 PM JST, Alexandre Courbot wrote: >> Trimming the two driver-owned slices of the command queue to the >> advertised length of a message is going to be used by both RPC and GMC >> messages, so factor that part out into a private function. >> >> The parsing itself can be improved by leveraging `split_at_checked` and >> `get`, so use them. >> >> No functional change intended. >> >> Suggested-by: Eliot Courtney >> Link: https://lore.kernel.org/all/DMN62G2CDG3N.ETT4GRFXWKKU@nvidia.com/ >> Signed-off-by: Alexandre Courbot >> --- >> drivers/gpu/nova-core/gsp/cmdq.rs | 21 +++++++++++++++++++++ >> drivers/gpu/nova-core/gsp/cmdq/rpc.rs | 20 +------------------- >> 2 files changed, 22 insertions(+), 19 deletions(-) >> >> diff --git a/drivers/gpu/nova-core/gsp/cmdq.rs b/drivers/gpu/nova-core/g= sp/cmdq.rs >> index 9dd11ac8952b..f3151aa8ea26 100644 >> --- a/drivers/gpu/nova-core/gsp/cmdq.rs >> +++ b/drivers/gpu/nova-core/gsp/cmdq.rs >> @@ -719,3 +719,24 @@ fn drain(&mut self) -> Result { >> } >> } >> } >> + >> +/// Helper function that trims the concatenation of `slice_1` and `slic= e_2` to `length`. >> +/// >> +/// Returns the truncated `(slice_1, slice_2)` pair, or `EIO` if `lengt= h > slice_1.len() + >> +/// slice_2.len()`. >> +fn trim_message_slice<'a>( >> + (slice_1, slice_2): (&'a [u8], &'a [u8]), >> + length: usize, >> +) -> Result<(&'a [u8], &'a [u8])> { >> + // See if `slice_1` covers the whole message, take it entirely if i= t doesn't. >> + let slice_1 =3D slice_1 >> + .split_at_checked(length) >> + .map(|split| split.0) >> + .unwrap_or(slice_1); >> + // `slice_2` is the remainder of the message not covered by `slice_= 1`. >> + let slice_2 =3D slice_2 >> + .get(..length.saturating_sub(slice_1.len())) >> + .ok_or(EIO)?; >> + >> + Ok((slice_1, slice_2)) >> +} > > I think .split_at_checked(length).map(|x| x.0) is the same as > .get(..length), so you can prolly just write: > > ``` > let slice_1 =3D slice_1.get(..length).unwrap_or(slice_1); Oh yeah, I was just too fixated on using `split_at_checked` and didn't notice using `get` directly was simpler, thanks! > let slice_2 =3D slice_2.get(..length - slice_1.len()).ok_or(EIO)?; > ``` > > Up to you if you want to use a checked_sub or saturating_sub but it's > locally clear that it won't underflow imo. Yes, this is indeed super trivial. It's actually one of the potential-panic= -site dilemmas where I have trouble deciding what to do. In the end for this one I've decided to go for your suggestion of using `-` with a `PANIC:` comment, as the panic site is eventually optimized away, and the generated assembly is the most efficient.