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

Johan Hovold johan at kernel.org
Thu Aug 3 06:14:44 PDT 2017

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

	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

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 at vger.kernel.org>	# 4.12
Cc: Robin Murphy <robin.murphy at arm.com>
Cc: Sricharan R <sricharan at codeaurora.org>
Cc: Stefan Wahren <stefan.wahren at i2se.com>
Reported-by: Hans Verkuil <hverkuil at xs4all.nl>
Signed-off-by: Johan Hovold <johan at kernel.org>

 - 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;
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.

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