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Date:   Tue, 22 Feb 2022 14:16:10 +0100
From:   'Christoph Hellwig' <hch@lst.de>
To:     David Laight <David.Laight@ACULAB.COM>
Cc:     'Christoph Hellwig' <hch@lst.de>,
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Subject: Re: [PATCH 22/22] mtd: rawnand: Use dma_alloc_noncoherent() for
 dma buffer
Message-ID: <20220222131610.GA10464@lst.de>
References: <20220219005221.634-1-bhe@redhat.com> <20220219005221.634-23-bhe@redhat.com> <20220219071900.GH26711@lst.de> <YhDSAJG+LksZSnLP@ip-172-31-19-208.ap-northeast-1.compute.internal> <20220222084652.GB6210@lst.de> <fe8deb6dd0b44a8a839820747451c37c@AcuMS.aculab.com>
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On Tue, Feb 22, 2022 at 09:06:48AM +0000, David Laight wrote:
> From: Christoph Hellwig
> > Sent: 22 February 2022 08:47
> ...
> > > Hmm.. for this specific case, What about allocating two buffers
> > > for DMA_TO_DEVICE and DMA_FROM_DEVICE at initialization time?
> > 
> > That will work, but I don't see the benefit as you'd still need to call
> > dma_sync_single* before and after each data transfer.
> 
> For systems with an iommu that should save all the iommu setup
> for every transfer.

So does allocating a single buffer as in the patch we are replying to.