netdev - Re: a saner API for allocating DMA addressable pages

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Message-ID: <20200825132612.GA22318@lst.de>
Date:   Tue, 25 Aug 2020 15:26:12 +0200
From:   Christoph Hellwig <hch@....de>
To:     Marek Szyprowski <m.szyprowski@...sung.com>
Cc:     Christoph Hellwig <hch@....de>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        "James E.J. Bottomley" <James.Bottomley@...senPartnership.com>,
        Joonyoung Shim <jy0922.shim@...sung.com>,
        Seung-Woo Kim <sw0312.kim@...sung.com>,
        Kyungmin Park <kyungmin.park@...sung.com>,
        Ben Skeggs <bskeggs@...hat.com>,
        Pawel Osciak <pawel@...iak.com>,
        Matt Porter <mporter@...nel.crashing.org>,
        iommu@...ts.linux-foundation.org,
        Tom Lendacky <thomas.lendacky@....com>,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-media@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-ia64@...r.kernel.org, linux-mips@...r.kernel.org,
        linux-parisc@...r.kernel.org, linux-samsung-soc@...r.kernel.org,
        nouveau@...ts.freedesktop.org, netdev@...r.kernel.org,
        linux-nvme@...ts.infradead.org, linux-scsi@...r.kernel.org,
        linux-mm@...ck.org, alsa-devel@...a-project.org
Subject: Re: a saner API for allocating DMA addressable pages

On Tue, Aug 25, 2020 at 01:30:41PM +0200, Marek Szyprowski wrote:
> I really wonder what is the difference between this new API and 
> alloc_pages(GFP_DMA, n). Is this API really needed? I thought that this 
> is legacy thing to be removed one day...

The difference is that the pages returned are guranteed to be addressable
by the devie.  This is a very important difference that matters for
a lot of use cases.