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    SubjectRe: [PATCH v2] dma-mapping: skip USB devices when configuring DMA during probe
    On Thu, Aug 03, 2017 at 04:23:08PM +0200, Johan Hovold wrote:
    > On Thu, Aug 03, 2017 at 10:04:21AM -0400, Alan Stern wrote:
    > > On Thu, 3 Aug 2017, Johan Hovold wrote:
    > >
    > > > USB devices use the DMA mask and offset of the controller, which have
    > > > already been setup when a device is probed. Note that modifying the
    > > > DMA mask of a USB device would change the mask for the controller (and
    > > > all devices on the bus) as the mask is literally shared.
    > > >
    > > > Since commit 2bf698671205 ("USB: of: fix root-hub device-tree node
    > > > handling"), of_dma_configure() would be called also for root hubs, which
    > > > use the device node of the controller. A separate, long-standing bug
    > > > that makes of_dma_configure() generate a 30-bit DMA mask from the RPI3's
    > > > "dma-ranges" would thus set a broken mask also for the controller. This
    > > > in turn prevents USB devices from enumerating when control transfers
    > > > fail:
    > > >
    > > > dwc2 3f980000.usb: Cannot do DMA to address 0x000000003a166a00
    > > >
    > > > Note that the aforementioned DMA-mask bug was benign for the HCD itself
    > > > as the dwc2 driver overwrites the mask previously set by
    > > > of_dma_configure() for the platform device in its probe callback. The
    > > > mask would only later get corrupted when the root-hub child device was
    > > > probed.
    > > >
    > > > Fix this, and similar future problems, by simply skipping USB devices
    > > > when dma_configure() is called during probe.
    > > >
    > > > Fixes: 09515ef5ddad ("of/acpi: Configure dma operations at probe time for platform/amba/pci bus devices")
    > > > Cc: stable <stable@vger.kernel.org> # 4.12
    > > > Cc: Robin Murphy <robin.murphy@arm.com>
    > > > Cc: Sricharan R <sricharan@codeaurora.org>
    > > > Cc: Stefan Wahren <stefan.wahren@i2se.com>
    > > > Reported-by: Hans Verkuil <hverkuil@xs4all.nl>
    > > > Signed-off-by: Johan Hovold <johan@kernel.org>
    > > > ---
    >
    > > > diff --git a/include/linux/usb.h b/include/linux/usb.h
    > > > index cb9fbd54386e..f86ad9d8c756 100644
    > > > --- a/include/linux/usb.h
    > > > +++ b/include/linux/usb.h
    > > > @@ -1222,6 +1222,11 @@ struct usb_device_driver {
    > > >
    > > > extern struct bus_type usb_bus_type;
    > > >
    > > > +static inline bool dev_is_usb(struct device *dev)
    > > > +{
    > > > + return dev->bus == &usb_bus_type;
    > > > +}
    > > > +
    > >
    > > Will this work if the USB subsystem is built as a module?
    >
    > Nope. :-/
    >
    > Add another flag (e.g. skip_dma_configure) to struct device for now?

    Or we can make sure that of_dma_configure() is only ever called for
    platform_devices by checking against platform_bus_type instead.

    I guess this was the intention of 09515ef5ddad ("of/acpi: Configure dma
    operations at probe time for platform/amba/pci bus devices") too.

    Thanks,
    Johan

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