linux-kernel - Re: [PATCH] dma-direct: avoid redundant memory sync for swiotlb

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Message-ID: <20220413164415.GA31640@lst.de>
Date:   Wed, 13 Apr 2022 18:44:15 +0200
From:   Christoph Hellwig <hch@....de>
To:     Robin Murphy <robin.murphy@....com>
Cc:     Christoph Hellwig <hch@....de>, Chao Gao <chao.gao@...el.com>,
        linux-kernel@...r.kernel.org, iommu@...ts.linux-foundation.org,
        m.szyprowski@...sung.com,
        Wang Zhaoyang1 <zhaoyang1.wang@...el.com>,
        Gao Liang <liang.gao@...el.com>,
        Kevin Tian <kevin.tian@...el.com>
Subject: Re: [PATCH] dma-direct: avoid redundant memory sync for swiotlb

On Wed, Apr 13, 2022 at 02:10:56PM +0100, Robin Murphy wrote:
> Are you sure? AFAICS swiotlb_map() does the right thing, and 
> dma_direct_{sync,unmap} are working off the DMA address, which is that of 
> the bounce slot when SWIOTLB is involved (not least, how would the 
> is_swiotlb_buffer() checks work otherwise?)

Yeah, actually this should be fine.