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charset=UTF-8 Date: Wed, 03 Jun 2026 10:34:05 +0900 Message-Id: From: "Alexandre Courbot" To: "Eliot Courtney" Cc: "John Hubbard" , "Danilo Krummrich" , "Timur Tabi" , "Alistair Popple" , "Shashank Sharma" , "Zhi Wang" , "David Airlie" , "Simona Vetter" , "Bjorn Helgaas" , "Miguel Ojeda" , "Alex Gaynor" , "Boqun Feng" , "Gary Guo" , =?utf-8?q?Bj=C3=B6rn_Roy_Baron?= , "Benno Lossin" , "Andreas Hindborg" , "Alice Ryhl" , "Trevor Gross" , , "LKML" Subject: Re: [PATCH v12 15/22] gpu: nova-core: Hopper/Blackwell: add FSP message infrastructure References: <20260602032111.224790-1-jhubbard@nvidia.com> <20260602032111.224790-16-jhubbard@nvidia.com> In-Reply-To: X-ClientProxiedBy: TY4P301CA0059.JPNP301.PROD.OUTLOOK.COM (2603:1096:405:36a::12) To CH2PR12MB3990.namprd12.prod.outlook.com (2603:10b6:610:28::18) Precedence: bulk X-Mailing-List: nova-gpu@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: CH2PR12MB3990:EE_|SN7PR12MB6716:EE_ X-MS-Office365-Filtering-Correlation-Id: 05505326-84bd-4a9c-e04c-08dec110354e X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|7416014|376014|366016|10070799003|56012099006|4143699003|11063799006|22082099003|18002099003; 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Add the queue >> registers and the low-level helpers used by the higher-level FSP >> message layer. >> >> Signed-off-by: John Hubbard >> --- >> drivers/gpu/nova-core/falcon/fsp.rs | 61 ++++++++++++++++++++++++++++- >> drivers/gpu/nova-core/regs.rs | 21 ++++++++++ >> 2 files changed, 80 insertions(+), 2 deletions(-) >> >> diff --git a/drivers/gpu/nova-core/falcon/fsp.rs b/drivers/gpu/nova-core= /falcon/fsp.rs >> index 6b057d958115..0ec1c55213bc 100644 >> --- a/drivers/gpu/nova-core/falcon/fsp.rs >> +++ b/drivers/gpu/nova-core/falcon/fsp.rs >> @@ -112,7 +112,6 @@ impl Falcon { >> /// >> /// `data` is interpreted as little-endian 32-bit words. Returns `E= INVAL` >> /// if `offset` or the `data` length is not 4-byte aligned. >> - #[expect(dead_code)] >> fn write_emem(&mut self, bar: &Bar0, offset: u32, data: &[u8]) -> R= esult { >> if offset % 4 !=3D 0 || data.len() % 4 !=3D 0 { >> return Err(EINVAL); >> @@ -131,7 +130,6 @@ fn write_emem(&mut self, bar: &Bar0, offset: u32, da= ta: &[u8]) -> Result { >> /// >> /// `data` is stored as little-endian 32-bit words. Returns `EINVAL= ` if >> /// `offset` or the `data` length is not 4-byte aligned. >> - #[expect(dead_code)] >> fn read_emem(&mut self, bar: &Bar0, offset: u32, data: &mut [u8]) -= > Result { >> if offset % 4 !=3D 0 || data.len() % 4 !=3D 0 { >> return Err(EINVAL); >> @@ -145,4 +143,63 @@ fn read_emem(&mut self, bar: &Bar0, offset: u32, da= ta: &mut [u8]) -> Result { >> =20 >> Ok(()) >> } >> + >> + /// Poll FSP for incoming data. >> + /// >> + /// Returns the size of available data in bytes, or 0 if no data is= available. >> + /// >> + /// The FSP message queue is not circular. Pointers are reset to 0 = after each >> + /// message exchange, so `tail >=3D head` is always true when data = is present. >> + #[expect(dead_code)] >> + pub(crate) fn poll_msgq(&self, bar: &Bar0) -> u32 { >> + let head =3D bar.read(regs::NV_PFSP_MSGQ_HEAD).address(); >> + let tail =3D bar.read(regs::NV_PFSP_MSGQ_TAIL).address(); >> + >> + if head =3D=3D tail { >> + return 0; >> + } >> + >> + // TAIL points at last DWORD written, so add 4 to get total siz= e >> + tail.saturating_sub(head) + 4 >> + } > > In a later patch, `send_sync_fsp` polls this then calls `recv_msg`. But, > structurally it's possible to pass in any size to `recv_msg` and read > more than we are supposed to. What about having `recv_msg` do the > polling to get the size and return a KVec with the read out data, > instead of `send_sync_fsp`? `poll_msgq` could stay private and we can > make it public later if we need to. The issue I see with returning a `KVec` is that it imposes a dynamic allocation for every message. Granted, this is what the current code does, but now that we have this `&mut self` logic in place that guarantees exclusive access, we can also turn the receiving `KVec` into a member of `Fsp` and keep passing it as a mut reference to avoid that. > >> + >> + /// Writes `packet` to FSP EMEM and updates the queue pointers to n= otify FSP. >> + /// >> + /// Returns `EINVAL` if `packet` is empty or its length is not 4-by= te aligned. >> + #[expect(dead_code)] >> + pub(crate) fn send_msg(&mut self, bar: &Bar0, packet: &[u8]) -> Res= ult { >> + if packet.is_empty() { >> + return Err(EINVAL); >> + } >> + >> + // Write message to EMEM at offset 0 (validates 4-byte alignmen= t) >> + self.write_emem(bar, 0, packet)?; >> + >> + // Update queue pointers. TAIL points at the last DWORD written= . >> + let tail_offset =3D u32::try_from(packet.len() - 4).map_err(|_|= EINVAL)?; >> + bar.write_reg(regs::NV_PFSP_QUEUE_TAIL::zeroed().with_address(t= ail_offset)); >> + bar.write_reg(regs::NV_PFSP_QUEUE_HEAD::zeroed().with_address(0= )); >> + >> + Ok(()) >> + } >> + >> + /// Reads `size` bytes from FSP EMEM into `buffer` and resets the q= ueue pointers. >> + /// >> + /// `size` comes from `poll_msgq`. Returns `EINVAL` if `size` is 0,= exceeds >> + /// `buffer`, or is not 4-byte aligned. >> + #[expect(dead_code)] >> + pub(crate) fn recv_msg(&mut self, bar: &Bar0, buffer: &mut [u8], si= ze: usize) -> Result { >> + if size =3D=3D 0 || size > buffer.len() { >> + return Err(EINVAL); >> + } >> + >> + // Read response from EMEM at offset 0 (validates 4-byte alignm= ent) >> + self.read_emem(bar, 0, &mut buffer[..size])?; >> + >> + // Reset message queue pointers after reading >> + bar.write_reg(regs::NV_PFSP_MSGQ_TAIL::zeroed().with_address(0)= ); >> + bar.write_reg(regs::NV_PFSP_MSGQ_HEAD::zeroed().with_address(0)= ); >> + >> + Ok(()) >> + } > > I think we can remove the `size` argument and have the caller pass in > an appropriately sized slice (altho obviated by my other comment). Agreed, having both a slice and a length parameter is redundant and requires extra checks that shouldn't be necessary. `recv_msg` is also called right after we resized the receiving vector to the right size, so we currently do have a call-time guarantee that `size =3D=3D buffer.len()`.