Re: [PATCH] swiotlb: ensure io_tlb_default_mem spinlock always initialised

[Ben Dooks]

On 11/07/2022 11:39, Christoph Hellwig wrote:
> On Mon, Jul 11, 2022 at 11:24:51AM +0100, Ben Dooks wrote:
> > On 11/07/2022 11:21, Christoph Hellwig wrote:
> > > On Mon, Jul 11, 2022 at 11:07:17AM +0100, Robin Murphy wrote:
> > > > If none of your peripherals should need SWIOTLB, then the fact that
> > > > you're ending up in swiotlb_map() at all is a clear sign that
> > > > something's wrong. Most likely someone's forgotten to set their DMA
> > > > masks correctly.
> > >
> > > Yes.
> >
> > Possibly, we had at least one driver which attempted to set a 32 bit
> > DMA mask which had to be removed as the DMA layer accepts this but
> > since there is no DMA32 memory the allocator then just fails.
> >
> > I expect the above may need to be a separate discussion(s) of how to
> > default the DMA mask and how to stop the implicit acceptance of setting
> > a 32-bit DMA mask.
>
> No.  Linux simply assumes you can do 32-bit DMA and this won't
> change.  So we'll need to fix your platform to support swiotlb
> eventually.

Ok, is there any examples currently in the kernel that have no memory
in the DMA32 zone that do use swiotlb?