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From: Scott Wood <oss@buserror.net>
To: Laurentiu Tudor <laurentiu.tudor@nxp.com>, Christian Zigotzky
 <chzigotzky@xenosoft.de>, "linuxppc-dev@lists.ozlabs.org"
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Date: Wed, 05 Sep 2018 13:39:04 -0500
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Subject: Re: FSL/NXP P5020: USB problems with the latest Git kernels
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On Wed, 2018-09-05 at 14:08 +0000, Laurentiu Tudor wrote:
> Hi Scott,
> 
> > -----Original Message----- 
> > On Mon, 2018-08-27 at 20:15 +0200, Christian Zigotzky wrote:
> > > Hello,
> > > 
> > > Our users tested the RC1 of kernel 4.19 on their P5020 boards today.
> > > Unfortunately the USB bug still exists. With mem values bigger than
> > 
> > 4096M,
> > > the USB mouse and keyboard doesn’t work. With the bootarg mem=4096M, the
> > 
> > USB
> > > devices work without any problems. Please compile the RC1 and test it on
> > > your P5020 board. There is a problem with the memory management since
> > > 22/08/18.
> > 
> > I just tested 4.19-rc1 on a T4240 and got a similar problem with MMC.  MMC
> > and
> > USB on these chips both have a 32-bit DMA limitation.  I'll look into it.
> 
> I encountered similar issues on LS104xA chips. This is the workaround for
> MMC:
> https://patchwork.kernel.org/patch/10506627/

That's not a workaround; it's the proper way to handle DMA addressing limits.

> On the USB side I didn't find a proper place in the usb subsystem code for a
> workaround but instead
> found an undocumented kernel arg (*) that limits the dma mask to 32 bits:
> xhci-hcd.quirks=0x800000.
> 
> (*) https://patchwork.kernel.org/patch/10509159/

The mask should already be getting set to 32 bits.  The problem is a recent
patch that changed initcall order, which lead to swiotlb not being used.  We
need to rework the swiotlb notifier so it doesn't depend on initcall ordering.

-Scott