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

From: Alan Stern
Date: Thu Aug 03 2017 - 10:04:29 EST

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@xxxxxxxxxxxxxxx> # 4.12
> Cc: Robin Murphy <robin.murphy@xxxxxxx>
> Cc: Sricharan R <sricharan@xxxxxxxxxxxxxx>
> Cc: Stefan Wahren <stefan.wahren@xxxxxxxx>
> Reported-by: Hans Verkuil <hverkuil@xxxxxxxxx>
> Signed-off-by: Johan Hovold <johan@xxxxxxxxxx>
> ---
> v2
> - amend commit message and point out that the long-standing 30-bit DMA-mask
> bug was benign to the dwc2 HCD itself (Robin)
> - add and use a new dev_is_usb() helper (Robin)

> 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?

Alan Stern