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

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Message-ID: <20241108200355.GC189042@unreal>
Date: Fri, 8 Nov 2024 22:03:55 +0200
From: Leon Romanovsky <leon@...nel.org>
To: Jonathan Corbet <corbet@....net>
Cc: 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>, 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

On Fri, Nov 08, 2024 at 12:34:21PM -0700, Jonathan Corbet wrote:
> 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?

Can I you please point me to commit/lore link/documentation with example
of such directive and I will do it?

Thanks

> 
> Thanks,
> 
> jon