linux-kernel - Re: [PATCH 05/16] dma-mapping: Introduce dma_map_sg

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Date:   Tue, 27 Apr 2021 20:01:13 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Logan Gunthorpe <logang@...tatee.com>
Cc:     linux-kernel@...r.kernel.org, linux-nvme@...ts.infradead.org,
        linux-block@...r.kernel.org, linux-pci@...r.kernel.org,
        linux-mm@...ck.org, iommu@...ts.linux-foundation.org,
        Stephen Bates <sbates@...thlin.com>,
        Christoph Hellwig <hch@....de>,
        Dan Williams <dan.j.williams@...el.com>,
        Christian König <christian.koenig@....com>,
        John Hubbard <jhubbard@...dia.com>,
        Don Dutile <ddutile@...hat.com>,
        Matthew Wilcox <willy@...radead.org>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        Jakowski Andrzej <andrzej.jakowski@...el.com>,
        Minturn Dave B <dave.b.minturn@...el.com>,
        Jason Ekstrand <jason@...kstrand.net>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Xiong Jianxin <jianxin.xiong@...el.com>,
        Bjorn Helgaas <helgaas@...nel.org>,
        Ira Weiny <ira.weiny@...el.com>,
        Robin Murphy <robin.murphy@....com>
Subject: Re: [PATCH 05/16] dma-mapping: Introduce dma_map_sg_p2pdma()

On Tue, Apr 27, 2021 at 04:55:45PM -0600, Logan Gunthorpe wrote:

> > Also, I see only 8 users of this function. How about just fix them all
> > to support negative returns and use this as the p2p API instead of
> > adding new API?
> 
> Well there might be 8 users of dma_map_sg_attrs() but there are a very
> large number of dma_map_sg(). Seems odd to me to single out the first as
> requiring these changes, but leave the latter.

At a high level I'm OK with it. dma_map_sg_attrs() is the extra
extended version of dma_map_sg(), it already has a different
signature, a different return code is not out of the question.

dma_map_sg() is just the simple easy to use interface that can't do
advanced stuff.

> I'm not that opposed to this. But it will make this series a fair bit
> longer to change the 8 map_sg_attrs() usages.

Yes, but the result seems much nicer to not grow the DMA API further.

Jason