Re: [PATCH v2] dma-mapping: skip USB devices when configuring DMA during probe

[Johan Hovold <johan@kernel.org>]

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?

Thanks,
Johan