linux-kernel - Re: [PATCH v1 09/17] docs: core-api: document the IOVA-based API

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Message-ID: <87ttchwmde.fsf@trenco.lwn.net>
Date: Fri, 08 Nov 2024 12:34:21 -0700
From: Jonathan Corbet <corbet@....net>
To: Leon Romanovsky <leon@...nel.org>, Jens Axboe <axboe@...nel.dk>, Jason
 Gunthorpe <jgg@...pe.ca>, Robin Murphy <robin.murphy@....com>, Joerg
 Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>, Christoph Hellwig
 <hch@....de>, Sagi Grimberg <sagi@...mberg.me>
Cc: Keith Busch <kbusch@...nel.org>, Bjorn Helgaas <bhelgaas@...gle.com>,
 Logan Gunthorpe <logang@...tatee.com>, Yishai Hadas <yishaih@...dia.com>,
 Shameer Kolothum <shameerali.kolothum.thodi@...wei.com>, Kevin Tian
 <kevin.tian@...el.com>, Alex Williamson <alex.williamson@...hat.com>,
 Marek Szyprowski <m.szyprowski@...sung.com>, Jérôme
 Glisse
 <jglisse@...hat.com>, Andrew Morton <akpm@...ux-foundation.org>,
 linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-block@...r.kernel.org, linux-rdma@...r.kernel.org,
 iommu@...ts.linux.dev, linux-nvme@...ts.infradead.org,
 linux-pci@...r.kernel.org, kvm@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH v1 09/17] docs: core-api: document the IOVA-based API

Leon Romanovsky <leon@...nel.org> writes:

> From: Christoph Hellwig <hch@....de>
>
> Add an explanation of the newly added IOVA-based mapping API.
>
> Signed-off-by: Christoph Hellwig <hch@....de>
> Signed-off-by: Leon Romanovsky <leonro@...dia.com>
> ---
>  Documentation/core-api/dma-api.rst | 70 ++++++++++++++++++++++++++++++
>  1 file changed, 70 insertions(+)
>
> diff --git a/Documentation/core-api/dma-api.rst b/Documentation/core-api/dma-api.rst
> index 8e3cce3d0a23..6095696a65a7 100644
> --- a/Documentation/core-api/dma-api.rst
> +++ b/Documentation/core-api/dma-api.rst
> @@ -530,6 +530,76 @@ routines, e.g.:::
>  		....
>  	}
>  
> +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 addresses
> +matter.  All the consideration from the previous section apply here as well.
> +
> +::
> +
> +    bool dma_iova_try_alloc(struct device *dev, struct dma_iova_state *state,
> +		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.

So, I see that you have nice kernel-doc comments for these; why not just
pull them in here with a kernel-doc directive rather than duplicating
the information?

Thanks,

jon