Re: [PATCH] usb: ehci: Enable support for 64bit EHCI host controllers in arm64

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On Thu, May 15, 2014 at 05:53:53PM +0100, Liviu Dudau wrote:
> On Thu, May 15, 2014 at 04:36:25PM +0100, Alan Stern wrote:
> > On Thu, 15 May 2014, Liviu Dudau wrote:
> > > On Thu, May 15, 2014 at 03:11:48PM +0100, Alan Stern wrote:
> > > > On Wed, 14 May 2014, Mark Brown wrote:
> > > > > arm64 architecture handles correctly 64bit DMAs and can enable support
> > > > > for 64bit EHCI host controllers.
> > > > 
> > > > Did you folks tested this for all sorts of host controllers?  I have no
> > > > way to verify that it works, and last I heard, many (or even most)  
> > > > controllers don't work right with 64-bit DMA.
> > > 
> > > I have tested it with a host controller that is capable of 64-bit DMA and
> > > without this change it doesn't work.
> > 
> > What do you mean it doesn't work?  Can't the host controller use 32-bit
> > DMA?
> 
> It could if arm64 would restrict the DMA addresses to 32-bit, but it doesn't
> and I end up on my platform with USB DMA buffers allocated >4GB address.

dma_alloc_coherent() on arm64 should return 32-bit addresses if the
coherent_dma_mask is set to 32-bit. Which kernel version is this?

-- 
Catalin
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