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Date:   Thu, 28 Feb 2019 15:04:35 -0800 (PST)
From:   Paul Walmsley <paul.walmsley@...ive.com>
To:     Alistair Francis <alistair23@...il.com>
cc:     Paul Walmsley <paul.walmsley@...ive.com>,
        Alistair Francis <Alistair.Francis@....com>,
        "linux-riscv@...ts.infradead.org" <linux-riscv@...ts.infradead.org>,
        "robh@...nel.org" <robh@...nel.org>,
        "robin.murphy@....com" <robin.murphy@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] Revert "of/device: Really only set bus DMA mask when
 appropriate"

On Thu, 28 Feb 2019, Alistair Francis wrote:

> On Thu, Feb 28, 2019 at 2:39 PM Paul Walmsley <paul.walmsley@...ive.com> wrote:
> > On Thu, 28 Feb 2019, Alistair Francis wrote:
> > > This reverts commit 6778be4e520959659b27a441c06a84c9cb009085.
> > >
> > > Reverting the commit fixes these error messages and an non-functioning
> > > USB bus when attaching a USB to PCIe card to a RISC-V board:
> > >     xhci_hcd 0000:03:00.0: Host took too long to start, waited 16000 microseconds.
> > >     xhci_hcd 0000:03:00.0: startup error -19
> > >     xhci_hcd 0000:03:00.0: USB bus 2 deregistered
> > >     xhci_hcd 0000:03:00.0: WARNING: Host System Error
> > >     xhci_hcd 0000:03:00.0: remove, state 1
> > >
> > > Signed-off-by: Alistair Francis <alistair.francis@....com>
> > > ---
> > > I'm not sure if this is the correct fix, it's possible something else is
> > > wrong, but I wanted to get some feedback.
> > >
> > > drivers/of/device.c | 4 +---
> > >  1 file changed, 1 insertion(+), 3 deletions(-)
> > >
> > > diff --git a/drivers/of/device.c b/drivers/of/device.c
> > > index 3717f2a20d0d..8299f8055da7 100644
> > > --- a/drivers/of/device.c
> > > +++ b/drivers/of/device.c
> > > @@ -149,11 +149,9 @@ int of_dma_configure(struct device *dev, struct device_node *np, bool force_dma)
> > >        * set by the driver.
> > >        */
> > >       mask = DMA_BIT_MASK(ilog2(dma_addr + size - 1) + 1);
> > > +     dev->bus_dma_mask = mask;
> > >       dev->coherent_dma_mask &= mask;
> > >       *dev->dma_mask &= mask;
> > > -     /* ...but only set bus mask if we found valid dma-ranges earlier */
> >
> > Does the DT data for the PCIe controller that you're using contain a
> > dma-ranges node?
> 
> Ah, no it does not. It only has ranges and bus-range [1].
> 
> Any idea what the dma-ranges should be?
> 
> 1: https://github.com/riscv/opensbi/blob/master/platform/sifive/fu540/HiFiveUnleashed-MicroSemi-Expansion.dts#L407

Not off the top of my head, but this may help:

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/devicetree/booting-without-of.txt#n1389

You might also consider grepping through existing DT data for examples of 
dma-ranges usage.

N.B., I have no direct knowledge of this, but have been told that some of 
the MicroSemi PCIe controllers can only bus-master into a 32-bit region.  
If this is a MicroSemi controller, that would need to be reflected in 
dma-ranges.


- Paul

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