Re: [PATCH] dma-direct: Set SG_DMA_SWIOTLB flag for dma-direct

[Robin Murphy]

On 08/05/2024 12:33 pm, Christoph Hellwig wrote:
> On Tue, May 07, 2024 at 01:07:25PM -0700, T.J. Mercier wrote:
> > On Mon, May 6, 2024 at 10:43???PM Christoph Hellwig <hch@xxxxxx> 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
>
> Whatever that code is doing is probably not upstream because it's too
> broken to live.

Indeed, at a glance it appears to be trying to reinvent 
dma_alloc_noncontiguous(). What's not immediately obvious is whether 
it's particular about allocations being DMA-contiguous; if not then I 
think it comes down to the same thing as vb2-dma-sg and the ideas we 
were tossing around for that[1].

Thanks,
Robin.

[1] 
https://lore.kernel.org/linux-media/20231228074645.765yytb2a7hvz7ti@xxxxxxxxxxxx/