linux-kernel - Re: [PATCH] swiotlb: sync buffer when mapping FROM

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Message-ID: <20190523164332.GA22245@lst.de>
Date:   Thu, 23 May 2019 18:43:32 +0200
From:   Christoph Hellwig <hch@....de>
To:     Marek Szyprowski <m.szyprowski@...sung.com>
Cc:     Robin Murphy <robin.murphy@....com>,
        Christoph Hellwig <hch@....de>,
        Horia Geantă <horia.geanta@....com>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        linux-imx@....com
Subject: Re: [PATCH] swiotlb: sync buffer when mapping FROM_DEVICE

On Thu, May 23, 2019 at 07:35:07AM +0200, Marek Szyprowski wrote:
> Don't we have DMA_BIDIRECTIONAL for such case?

Not sure if it was intended for that case, but it definitively should
do the right thing for swiotlb, and it should also do the right thing
in terms of cache maintainance.

> Maybe we should update 
> documentation a bit to point that DMA_FROM_DEVICE expects the whole 
> buffer to be filled by the device?

Probably. Horia, can you try to use DMA_BIDIRECTIONAL?