From mboxrd@z Thu Jan  1 00:00:00 1970
From: Christoph Hellwig <hch@lst.de>
Subject: Re: a saner API for allocating DMA addressable pages
Date: Tue, 25 Aug 2020 15:26:12 +0200
Message-ID: <20200825132612.GA22318@lst.de>
References: <CGME20200819065610eucas1p2fde88e81917071b1888e7cc01ba0f298@eucas1p2.samsung.com> <20200819065555.1802761-1-hch@lst.de> <8fa1ce36-c783-1a02-6890-211eb504a33b@samsung.com>
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To: Marek Szyprowski <m.szyprowski@samsung.com>
Cc: Christoph Hellwig <hch@lst.de>, Mauro Carvalho Chehab <mchehab@kernel.org>, Thomas Bogendoerfer <tsbogend@alpha.franken.de>, "James E.J. Bottomley" <James.Bottomley@HansenPartnership.com>, Joonyoung Shim <jy0922.shim@samsung.com>, Seung-Woo Kim <sw0312.kim@samsung.com>, Kyungmin Park <kyungmin.park@samsung.com>, Ben Skeggs <bskeggs@redhat.com>, Pawel Osciak <pawel@osciak.com>, Matt Porter <mporter@kernel.crashing.org>, iommu@lists.linux-foundation.org, Tom Lendacky <thomas.lendacky@amd.com>, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-media@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-ia64@vger.kernel.org, linux-mips@vger.kernel.org, linux-parisc@vger.kernel.org, linux-samsung-soc@vger.kernel.org, nouveau@lists.freedesktop.
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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.