linux-kernel - Re: [PATCH 05/28] media/v4l2: remove V4L2-FLAG-MEMORY-NON-CONSISTENT

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Message-ID: <20200819135738.GB17098@lst.de>
Date:   Wed, 19 Aug 2020 15:57:38 +0200
From:   Christoph Hellwig <hch@....de>
To:     Tomasz Figa <tfiga@...omium.org>
Cc:     Robin Murphy <robin.murphy@....com>,
        Christoph Hellwig <hch@....de>, alsa-devel@...a-project.org,
        linux-ia64@...r.kernel.org,
        Linux Doc Mailing List <linux-doc@...r.kernel.org>,
        nouveau@...ts.freedesktop.org, linux-nvme@...ts.infradead.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "James E.J. Bottomley" <James.Bottomley@...senpartnership.com>,
        linux-mm@...ck.org, Marek Szyprowski <m.szyprowski@...sung.com>,
        linux-samsung-soc <linux-samsung-soc@...r.kernel.org>,
        Joonyoung Shim <jy0922.shim@...sung.com>,
        linux-scsi@...r.kernel.org,
        Kyungmin Park <kyungmin.park@...sung.com>,
        Ben Skeggs <bskeggs@...hat.com>,
        Matt Porter <mporter@...nel.crashing.org>,
        Linux Media Mailing List <linux-media@...r.kernel.org>,
        Tom Lendacky <thomas.lendacky@....com>,
        Pawel Osciak <pawel@...iak.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        "list@....net:IOMMU DRIVERS" <iommu@...ts.linux-foundation.org>,
        Joerg Roedel <joro@...tes.org>,
        "list@....net:IOMMU DRIVERS <iommu@...ts.linux-foundation.org>, Joerg
        Roedel <joro@...tes.org>," <linux-arm-kernel@...ts.infradead.org>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        linux-parisc@...r.kernel.org, netdev@...r.kernel.org,
        Seung-Woo Kim <sw0312.kim@...sung.com>,
        linux-mips@...r.kernel.org
Subject: Re: [PATCH 05/28] media/v4l2: remove
 V4L2-FLAG-MEMORY-NON-CONSISTENT

On Wed, Aug 19, 2020 at 02:49:01PM +0200, Tomasz Figa wrote:
> With the default config it doesn't, but with
> CONFIG_DMA_NONCOHERENT_CACHE_SYNC enabled it makes dma_pgprot() keep
> the pgprot value as is, without enforcing coherence attributes.

Which isn't selected on arm64, and that is for a good reason.

> AFAIK dma_cache_sync() isn't the only way to perform the cache
> synchronization.

Yes, it is the only documented way to do it.  And if you read the whole
series instead of screaming you'd see that it provides a proper way
to deal with non-coherent memory which will also work with arm64.
instead of screaming 

> By the way, as a videobuf2 reviewer, I'd appreciate being CC'd on any
> series related to the subsystem-facing DMA API changes, since
> videobuf2 is one of the biggest users of it.

The cc list is too long - I cc lists and key maintainers.  As a reviewer
should should watch your subsystems lists closely.