linux-kernel - Re: [PATCH 08/28] MIPS: make dma_sync_*_for

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Message-ID: <20200901135304.GC11944@alpha.franken.de>
Date:   Tue, 1 Sep 2020 15:53:04 +0200
From:   Thomas Bogendoerfer <tsbogend@...ha.franken.de>
To:     Christoph Hellwig <hch@....de>
Cc:     Mauro Carvalho Chehab <mchehab@...nel.org>,
        "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>,
        Marek Szyprowski <m.szyprowski@...sung.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: [PATCH 08/28] MIPS: make dma_sync_*_for_cpu a little less
 overzealous

On Wed, Aug 19, 2020 at 08:55:35AM +0200, Christoph Hellwig wrote:
> When transferring DMA ownership back to the CPU there should never
> be any writeback from the cache, as the buffer was owned by the
> device until now.  Instead it should just be invalidated for the
> mapping directions where the device could have written data.
> Note that the changes rely on the fact that kmap_atomic is stubbed
> out for the !HIGHMEM case to simplify the code a bit.
> 
> Signed-off-by: Christoph Hellwig <hch@....de>
> ---
>  arch/mips/mm/dma-noncoherent.c | 44 +++++++++++++++++++++-------------
>  1 file changed, 28 insertions(+), 16 deletions(-)

Acked-by: Thomas Bogendoerfer <tsbogend@...ha.franken.de>

-- 
Crap can work. Given enough thrust pigs will fly, but it's not necessarily a
good idea.                                                [ RFC1925, 2.3 ]