Re: DMABOUNCE in pci-rcar

[Ben Dooks]

On 20/03/14 17:09, Arnd Bergmann wrote:
> On Thursday 20 March 2014 16:04:36 Ben Dooks wrote:
> > On 26/02/14 20:57, Arnd Bergmann wrote:
> > > On Wednesday 26 February 2014 12:48:17 Bjorn Helgaas wrote:
> > > > On Mon, Feb 24, 2014 at 4:00 AM, Arnd Bergmann <arnd@xxxxxxxx> wrote:
> > > > > Hi Magnus,
> > > > >
> > > > > I noticed during randconfig testing that you enabled DMABOUNCE for the
> > > > > pci-rcar-gen2 driver as posted in this patch https://lkml.org/lkml/2014/2/5/30
> > > > >
> > > > > I didn't see the original post unfortunately, but I fear we have to
> > > > > revert it and come up with a better solution, ...
> > > >
> > > > Sounds like I should drop the following patches from my pci/host-rcar
> > > > branch for now?
> > > >
> > > >     PCI: rcar: Add DMABOUNCE support
> > > >     PCI: rcar: Enable BOUNCE in case of HIGHMEM
> > > >     PCI: rcar: Make the Kconfig dependencies more generic
> > >
> > > Sounds good to me. The last patch is actually fine, but you'll have to
> > > fix the context to apply it without the other two.
> >
> > As a note, if we now boot a Lager with DT on 3.14-rc3 series the USB
> > controllers no longer work with full 2GiB RAM enabled in the device
> > tree.
>
> Did it work before these patches got applied initially?

It did, but I cannot remember if we where limiting DRAM to 1GiB
or not.

> > Could we work around this by having 1GiB of memory defined in the
> > 32bit memory and then add the rest of the 3GiB from the >32bit
> > area via LPAE? Will the kernel ever try to allocate DMA memory from
> > anything >32bit?
>
> You can solve the case for dma_alloc_coherent() this way, or by
> setting the mask correctly. It won't help you for dma_map_* though,
> which still requires someone to add support for swiotlb or using
> an IOMMU if present.

We do not have an IOMMU present at the moment. Not sure how
to go about setting a mask on a pci-probed device.


--
Ben Dooks				http://www.codethink.co.uk/
Senior Engineer				Codethink - Providing Genius
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