From nobody Tue Dec 16 21:57:56 2025 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 610AB27CB36; Wed, 23 Apr 2025 08:14:36 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1745396076; cv=none; b=UVw4+Uawx2yiq5O+Px6svS0iCEHPv5iMDSQUny7noiy2DWsdJWfaOmVz3EPJsXo3TmYsGDjypPh05+M0stYOAnYXWF40/TQDa/xwTaNJhchLcTTzoNcMl3Uw73AKtTGQw5/nKS8QfFr98hHp71J9z+md7oHfIuWkmx5t6LBbCPc= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1745396076; c=relaxed/simple; bh=d1+z79zg+kihe5QDvuiZPuBTqwMqD9eJrziwPARATZw=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=K2JcvhPi/6woJCsVXdy50zEKYRVn1nk3rH1u87k6fvs6WQJHgPobE+Cav6ApLRlCNJfK4lmrckgR1XNV0qt967wbaPrFUxcp1HeEwYOea5NLNHDNH7whL3PjoDQV9eYKwK81uSfmqVPADSLw0GKlVno5E+R+0/xdBjM72A9jNAw= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=pxwe7iTc; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="pxwe7iTc" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 7F16CC4CEE2; Wed, 23 Apr 2025 08:14:35 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1745396076; bh=d1+z79zg+kihe5QDvuiZPuBTqwMqD9eJrziwPARATZw=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=pxwe7iTcgrDrrJrmcOzX972ifQ9D6JVEhDyjPcwwbwuVl5WBAXYDa/8l4DwaLlO1Y vWsvyN8+xhjntksq9HHQv/U5yDIQ7bXtbs603iaK9U11b3NwRT8KTo7Y16zEYpBwAb tekXO0ynYv4MEb0+spPpvw7nl4VYxfxNCatQQ4wLsfvGxwO1M7Nx+Fq7d37PGV8eWi FEqyUa6I1tPF5wbesUJJBhjietyGAKhO/Ixdu0i9NC9A91a0SuSF5RdIyowf8I/PLc cdrRTsuDCiC9V64kjPfH592VX/vNZGPVXZWQfZlhD2D+uTZMCYmKBCur2EngxrpVBY rnT3jQf4b8oTQ== From: Leon Romanovsky To: Marek Szyprowski , Jens Axboe , Christoph Hellwig , Keith Busch Cc: Jake Edge , Jonathan Corbet , Jason Gunthorpe , Zhu Yanjun , Robin Murphy , Joerg Roedel , Will Deacon , Sagi Grimberg , Bjorn Helgaas , Logan Gunthorpe , Yishai Hadas , Shameer Kolothum , Kevin Tian , Alex Williamson , =?UTF-8?q?J=C3=A9r=C3=B4me=20Glisse?= , Andrew Morton , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-block@vger.kernel.org, linux-rdma@vger.kernel.org, iommu@lists.linux.dev, linux-nvme@lists.infradead.org, linux-pci@vger.kernel.org, kvm@vger.kernel.org, linux-mm@kvack.org, Niklas Schnelle , Chuck Lever , Luis Chamberlain , Matthew Wilcox , Dan Williams , Kanchan Joshi , Chaitanya Kulkarni , Leon Romanovsky Subject: [PATCH v9 09/24] docs: core-api: document the IOVA-based API Date: Wed, 23 Apr 2025 11:13:00 +0300 Message-ID: <7d5cf410e923a22c519ea60f4f35e3c9f8f845e3.1745394536.git.leon@kernel.org> X-Mailer: git-send-email 2.49.0 In-Reply-To: References: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Christoph Hellwig Add an explanation of the newly added IOVA-based mapping API. Signed-off-by: Christoph Hellwig Tested-by: Jens Axboe Signed-off-by: Leon Romanovsky --- Documentation/core-api/dma-api.rst | 71 ++++++++++++++++++++++++++++++ 1 file changed, 71 insertions(+) diff --git a/Documentation/core-api/dma-api.rst b/Documentation/core-api/dm= a-api.rst index 8e3cce3d0a23..2ad08517e626 100644 --- a/Documentation/core-api/dma-api.rst +++ b/Documentation/core-api/dma-api.rst @@ -530,6 +530,77 @@ routines, e.g.::: .... } =20 +Part Ie - IOVA-based DMA mappings +--------------------------------- + +These APIs allow a very efficient mapping when using an IOMMU. They are an +optional path that requires extra code and are only recommended for drivers +where DMA mapping performance, or the space usage for storing the DMA addr= esses +matter. All the considerations from the previous section apply here as we= ll. + +:: + + bool dma_iova_try_alloc(struct device *dev, struct dma_iova_state *sta= te, + phys_addr_t phys, size_t size); + +Is used to try to allocate IOVA space for mapping operation. If it returns +false this API can't be used for the given device and the normal streaming +DMA mapping API should be used. The ``struct dma_iova_state`` is allocated +by the driver and must be kept around until unmap time. + +:: + + static inline bool dma_use_iova(struct dma_iova_state *state) + +Can be used by the driver to check if the IOVA-based API is used after a +call to dma_iova_try_alloc. This can be useful in the unmap path. + +:: + + int dma_iova_link(struct device *dev, struct dma_iova_state *state, + phys_addr_t phys, size_t offset, size_t size, + enum dma_data_direction dir, unsigned long attrs); + +Is used to link ranges to the IOVA previously allocated. The start of all +but the first call to dma_iova_link for a given state must be aligned +to the DMA merge boundary returned by ``dma_get_merge_boundary())``, and +the size of all but the last range must be aligned to the DMA merge bounda= ry +as well. + +:: + + int dma_iova_sync(struct device *dev, struct dma_iova_state *state, + size_t offset, size_t size); + +Must be called to sync the IOMMU page tables for IOVA-range mapped by one = or +more calls to ``dma_iova_link()``. + +For drivers that use a one-shot mapping, all ranges can be unmapped and the +IOVA freed by calling: + +:: + + void dma_iova_destroy(struct device *dev, struct dma_iova_state *state, + size_t mapped_len, enum dma_data_direction dir, + unsigned long attrs); + +Alternatively drivers can dynamically manage the IOVA space by unmapping +and mapping individual regions. In that case + +:: + + void dma_iova_unlink(struct device *dev, struct dma_iova_state *state, + size_t offset, size_t size, enum dma_data_direction dir, + unsigned long attrs); + +is used to unmap a range previously mapped, and + +:: + + void dma_iova_free(struct device *dev, struct dma_iova_state *state); + +is used to free the IOVA space. All regions must have been unmapped using +``dma_iova_unlink()`` before calling ``dma_iova_free()``. =20 Part II - Non-coherent DMA allocations -------------------------------------- --=20 2.49.0