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

[Robin Murphy]

On 03/08/17 14:14, 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>

Reviewed-by: Robin Murphy <robin.murphy@xxxxxxx>

> ---
> 
> 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)
> 
> 
>  drivers/base/dma-mapping.c | 8 ++++++++
>  include/linux/usb.h        | 5 +++++
>  2 files changed, 13 insertions(+)
> 
> diff --git a/drivers/base/dma-mapping.c b/drivers/base/dma-mapping.c
> index b555ff9dd8fc..604e99e6660a 100644
> --- a/drivers/base/dma-mapping.c
> +++ b/drivers/base/dma-mapping.c
> @@ -13,6 +13,7 @@
>  #include <linux/gfp.h>
>  #include <linux/of_device.h>
>  #include <linux/slab.h>
> +#include <linux/usb.h>
>  #include <linux/vmalloc.h>
>  
>  /*
> @@ -345,6 +346,10 @@ int dma_configure(struct device *dev)
>  	enum dev_dma_attr attr;
>  	int ret = 0;
>  
> +	/* USB devices share the controller's mask. */
> +	if (dev_is_usb(dev))
> +		return 0;
> +
>  	if (dev_is_pci(dev)) {
>  		bridge = pci_get_host_bridge_device(to_pci_dev(dev));
>  		dma_dev = bridge;
> @@ -369,6 +374,9 @@ int dma_configure(struct device *dev)
>  
>  void dma_deconfigure(struct device *dev)
>  {
> +	if (dev_is_usb(dev))
> +		return;
> +
>  	of_dma_deconfigure(dev);
>  	acpi_dma_deconfigure(dev);
>  }
> 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;
> +}
> +
>  /**
>   * struct usb_class_driver - identifies a USB driver that wants to use the USB major number
>   * @name: the usb class device name for this driver.  Will show up in sysfs.
>