linux-kernel - Re: [patch] media: videobuf-dma-sg: Clear dma coherent buf only once

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Message-ID: <20190327082501.GM20525@lst.de>
Date:   Wed, 27 Mar 2019 09:25:01 +0100
From:   " Christoph Hellwig <hch@....de>" <hch@....de>
To:     Hillf Danton <hdanton@...a.com>
Cc:     "linux-media@...r.kernel.org" <linux-media@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        " Christoph Hellwig <hch@....de>" <hch@....de>,
        " Marek Szyprowski <m.szyprowski@...sung.com>" 
        <m.szyprowski@...sung.com>,
        " Will Deacon <will.deacon@....com>" <will.deacon@....com>,
        " Mauro Carvalho Chehab <mchehab@...nel.org>" <mchehab@...nel.org>
Subject: Re: [patch] media: videobuf-dma-sg: Clear dma coherent buf only
 once

On Thu, Mar 21, 2019 at 06:36:21PM +0800, Hillf Danton wrote:
> On both the arch and dma core sides, see commit 6829e274a623 and 518a2f1925c3
> respectively, efforts are paid for clearing memory returned from dma_alloc_*
> functions, so on the driver side we can get our duty offloaded by explicitly
> asking the dma core for a zero-ed buffer.

And why do you think you then need to pass __GFP_ZERO?