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charset=UTF-8 Date: Fri, 27 Mar 2026 00:04:04 +0900 Message-Id: Subject: Re: [PATCH 4/7] gpu: nova-core: falcon: use dma::Coherent From: "Alexandre Courbot" To: "Eliot Courtney" Cc: "Danilo Krummrich" , "Abdiel Janulgue" , "Daniel Almeida" , "Robin Murphy" , "Andreas Hindborg" , "Miguel Ojeda" , "Boqun Feng" , "Gary Guo" , =?utf-8?q?Bj=C3=B6rn_Roy_Baron?= , "Benno Lossin" , "Alice Ryhl" , "Trevor Gross" , "David Airlie" , "Simona Vetter" , "John Hubbard" , "Alistair Popple" , "Joel Fernandes" , "Timur Tabi" , "Zhi Wang" , , , References: <20260321-b4-nova-dma-removal-v1-0-5cf18a75ff64@nvidia.com> <20260321-b4-nova-dma-removal-v1-4-5cf18a75ff64@nvidia.com> In-Reply-To: X-ClientProxiedBy: OS7PR01CA0125.jpnprd01.prod.outlook.com (2603:1096:604:24e::12) 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_|PH7PR12MB6418:EE_ X-MS-Office365-Filtering-Correlation-Id: 112996a3-324c-4d6e-5350-08de8b48ee5f X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|10070799003|366016|7416014|376014|22082099003|18002099003|56012099003; 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>> =20 >> use crate::{ >> - dma::DmaObject, >> driver::Bar0, >> falcon::hal::LoadMethod, >> gpu::Chipset, >> @@ -636,7 +636,7 @@ pub(crate) fn pio_load + FalconPioLoadable>( >> fn dma_wr( >> &self, >> bar: &Bar0, >> - dma_obj: &DmaObject, >> + dma_obj: &Coherent<[u8]>, >> target_mem: FalconMem, >> load_offsets: FalconDmaLoadTarget, >> ) -> Result { >> @@ -740,7 +740,7 @@ fn dma_load + Falcon= DmaLoadable>( >> fw: &F, >> ) -> Result { >> // Create DMA object with firmware content as the source of the= DMA engine. >> - let dma_obj =3D DmaObject::from_data(dev, fw.as_slice())?; >> + let dma_obj =3D Coherent::from_slice(dev, fw.as_slice(), GFP_KE= RNEL)?; > > Is it guaranteed that fw.as_slice() is a multiple of 256 in size? > In `dma_wr` it breaks this up into 256 byte transfers. Since this > no longer pads out to a page boundary, it means that it could now error > (around "DMA transfer goes beyond range of DMA object") if the Dmem=20 > section's size is not divisible by 256. But tbh, I find it odd that=20 > `dma_wr` doesn't check that FalconDmaLoadTarget's length is a > multiple of 256 anyway, because it looks like it'll write a bunch of > unrelated bytes (since it rounds up to the nearest 256 to copy). > > Maybe we should enforce that `FalconDmaLoadTarget` length is divisible > by 256? > > For this series if for all firmwares it's divisible by 256 then I think > it's fine to leave this as is for now, but I do find the lack of > checking in `dma_wr` (or anywhere else for FalconDmaLoadTarget) a bit > odd. All coherent allocations are page-aligned (and use full pages), so we are safe in terms of overflows. Also `dma_wr` uses `div_ceil(256)` which will skip the last data block entirely if it is not a multiple of 256. It might be a bit more robust to explicitly check that the size is a multiple of 256 and return an error if that is not the case indeed.