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charset=UTF-8 Date: Fri, 27 Feb 2026 20:28:57 +0900 Message-Id: From: "Alexandre Courbot" To: "Eliot Courtney" Cc: "Danilo Krummrich" , "Alice Ryhl" , "David Airlie" , "Simona Vetter" , "Miguel Ojeda" , "Boqun Feng" , "Gary Guo" , =?utf-8?q?Bj=C3=B6rn_Roy_Baron?= , "Benno Lossin" , "Andreas Hindborg" , "Trevor Gross" , , , , , "Zhi Wang" Subject: Re: [PATCH v3 8/9] gpu: nova-core: gsp: support large RPCs via continuation record References: <20260226-cmdq-continuation-v3-0-572ab9916766@nvidia.com> <20260226-cmdq-continuation-v3-8-572ab9916766@nvidia.com> In-Reply-To: <20260226-cmdq-continuation-v3-8-572ab9916766@nvidia.com> X-ClientProxiedBy: TYCP286CA0112.JPNP286.PROD.OUTLOOK.COM (2603:1096:400:29c::7) To CH2PR12MB3990.namprd12.prod.outlook.com (2603:10b6:610:28::18) Precedence: bulk X-Mailing-List: rust-for-linux@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: CH2PR12MB3990:EE_|SJ0PR12MB7460:EE_ X-MS-Office365-Filtering-Correlation-Id: ffd1a77c-b0a4-492c-3138-08de75f367a2 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|366016|7416014|376014|1800799024|10070799003; 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> + > + self.send_single_command(bar, state.command(command))?; As we discussed offline these two lines were bothering me a bit, because we pass `command` twice and there is a possibility (although purely hypothetical) of API misuse. I think I found a way around it: we turn `SplitState` into an enum with a `Single` variant, that contains the original command, and a `Split` one, which contains the truncated initial command and its continuation records. This simple change cascades into more simplifications in the new types introduced by this patch: `SplitCommand` is not an enum anymore, but the original command with a shorter payload. And the continuation records are their own self-contained type. This is achieved by allocating two `KVVec`s when we split, and taking advantage of the `SBuffer` we conveniently have at hand to fill them both. I have pushed a branch with this idea implemented on top of yours in [1] - please check it, but I think it brings a nice (if small) incremental improvement. It removes the API misuse potential, makes every type purely single-purpose, and doesn't need `PhantomData` or lifetimes, making it simpler overall IMHO. [1] https://github.com/Gnurou/linux/tree/review/continuations > + > + while let Some(continuation) =3D state.next_continuation_record(= ) { > + dev_dbg!( > + &self.dev, > + "GSP RPC: send continuation: size=3D0x{:x}\n", > + command_size(&continuation), > + ); `send_single_command` should already print the command, so I don't think we need this additional debug print? > + // Turbofish needed because the compiler cannot infer M here= . > + self.send_single_command::>(bar, cont= inuation)?; > + } > + > + Ok(()) > + } > + > /// Wait for a message to become available on the message queue. > /// > /// This works purely at the transport layer and does not interpret = or validate the message > diff --git a/drivers/gpu/nova-core/gsp/commands.rs b/drivers/gpu/nova-cor= e/gsp/commands.rs > index 8f270eca33be..6ffd0b9cbf05 100644 > --- a/drivers/gpu/nova-core/gsp/commands.rs > +++ b/drivers/gpu/nova-core/gsp/commands.rs > @@ -4,6 +4,7 @@ > array, > convert::Infallible, > ffi::FromBytesUntilNulError, > + marker::PhantomData, > str::Utf8Error, // > }; > =20 > @@ -22,13 +23,16 @@ > driver::Bar0, > gsp::{ > cmdq::{ > + command_size, > Cmdq, > CommandToGsp, > MessageFromGsp, // > }, > fw::{ > commands::*, > - MsgFunction, // > + GspMsgElement, > + MsgFunction, > + GSP_MSG_QUEUE_ELEMENT_SIZE_MAX, // > }, > }, > sbuffer::SBufferIter, > @@ -242,3 +246,141 @@ pub(crate) fn get_gsp_info(cmdq: &mut Cmdq, bar: &B= ar0) -> Result } > } > } > + > +/// The `ContinuationRecord` command. > +pub(crate) struct ContinuationRecord<'a> { These new types are to be used by the command queue, and we don't want to use them elsewhere, so `pub(super)` seems more appropriate to me. And actually, since they are more command queue infrastructure than pure "commands" that fulfill a given purpose, I'd suggest moving them into their own sub-module of `gsp` (named `continuation` or `split` maybe?). That way they don't get in the way of readers who just want to learn about GSP commands.