netdev - Re: [PATCH 22/22] mtd: rawnand: Use dma_alloc

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Message-ID: <20220222131610.GA10464@lst.de>
Date:   Tue, 22 Feb 2022 14:16:10 +0100
From:   'Christoph Hellwig' <hch@....de>
To:     David Laight <David.Laight@...LAB.COM>
Cc:     'Christoph Hellwig' <hch@....de>,
        Hyeonggon Yoo <42.hyeyoo@...il.com>,
        Baoquan He <bhe@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "cl@...ux.com" <cl@...ux.com>,
        "penberg@...nel.org" <penberg@...nel.org>,
        "rientjes@...gle.com" <rientjes@...gle.com>,
        "iamjoonsoo.kim@....com" <iamjoonsoo.kim@....com>,
        "vbabka@...e.cz" <vbabka@...e.cz>,
        "david@...hat.com" <david@...hat.com>,
        "herbert@...dor.apana.org.au" <herbert@...dor.apana.org.au>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "linux-crypto@...r.kernel.org" <linux-crypto@...r.kernel.org>,
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        "wsa@...nel.org" <wsa@...nel.org>
Subject: Re: [PATCH 22/22] mtd: rawnand: Use dma_alloc_noncoherent() for
 dma buffer

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.