linux-kernel - Re: [PATCH] dma-direct: Set SG_DMA

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Message-ID: <CABdmKX3PgcXaRUH3L7OV+POMiMd5L6pEF4fLXYPgfmQUNu_trg@mail.gmail.com>
Date: Tue, 7 May 2024 13:07:25 -0700
From: "T.J. Mercier" <tjmercier@...gle.com>
To: Christoph Hellwig <hch@....de>
Cc: Marek Szyprowski <m.szyprowski@...sung.com>, Robin Murphy <robin.murphy@....com>, 
	isaacmanjarres@...gle.com, Catalin Marinas <catalin.marinas@....com>, iommu@...ts.linux.dev, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] dma-direct: Set SG_DMA_SWIOTLB flag for dma-direct

On Mon, May 6, 2024 at 10:43 PM Christoph Hellwig <hch@....de> wrote:
>
> On Mon, May 06, 2024 at 09:39:53AM -0700, T.J. Mercier wrote:
> > > You should not check, you simply must handle it by doing the proper
> > > DMA API based ownership management.
> >
> > That doesn't really work for uncached buffers.
>
> What uncached buffers?

For example these ones:
https://android.googlesource.com/kernel/common/+/refs/heads/android-mainline/drivers/dma-buf/heaps/system_heap.c#141

Vendors have their own drivers that also export uncached buffers in a
similar way.