[PATCH v3] dma-mapping: skip USB devices when configuring DMA during probe

[Johan Hovold]

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 adding a flag to struct device
which prevents driver core from calling dma_configure() during probe and
making sure it is set for USB devices.

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>
---

v3
 - add flag to struct device to prevent DMA configuration during probe instead
   of checking for the USB bus type, which is not available when USB is built
   as a module as noted by Alan
 - drop moderated rpi list from CC

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 | 6 ++++++
 drivers/usb/core/usb.c     | 1 +
 include/linux/device.h     | 3 +++
 3 files changed, 10 insertions(+)

diff --git a/drivers/base/dma-mapping.c b/drivers/base/dma-mapping.c
index b555ff9dd8fc..f9f703be0ad1 100644
--- a/drivers/base/dma-mapping.c
+++ b/drivers/base/dma-mapping.c
@@ -345,6 +345,9 @@ int dma_configure(struct device *dev)
 	enum dev_dma_attr attr;
 	int ret = 0;
 
+	if (dev->skip_dma_configure)
+		return 0;
+
 	if (dev_is_pci(dev)) {
 		bridge = pci_get_host_bridge_device(to_pci_dev(dev));
 		dma_dev = bridge;
@@ -369,6 +372,9 @@ int dma_configure(struct device *dev)
 
 void dma_deconfigure(struct device *dev)
 {
+	if (dev->skip_dma_configure)
+		return;
+
 	of_dma_deconfigure(dev);
 	acpi_dma_deconfigure(dev);
 }
diff --git a/drivers/usb/core/usb.c b/drivers/usb/core/usb.c
index 17681d5638ac..2a85d905b539 100644
--- a/drivers/usb/core/usb.c
+++ b/drivers/usb/core/usb.c
@@ -588,6 +588,7 @@ struct usb_device *usb_alloc_dev(struct usb_device *parent,
 	 * Note: calling dma_set_mask() on a USB device would set the
 	 * mask for the entire HCD, so don't do that.
 	 */
+	dev->dev.skip_dma_configure = true;
 	dev->dev.dma_mask = bus->sysdev->dma_mask;
 	dev->dev.dma_pfn_offset = bus->sysdev->dma_pfn_offset;
 	set_dev_node(&dev->dev, dev_to_node(bus->sysdev));
diff --git a/include/linux/device.h b/include/linux/device.h
index 723cd54b94da..022cf258068b 100644
--- a/include/linux/device.h
+++ b/include/linux/device.h
@@ -877,6 +877,8 @@ struct dev_links_info {
  * @offline:	Set after successful invocation of bus type's .offline().
  * @of_node_reused: Set if the device-tree node is shared with an ancestor
  *              device.
+ * @skip_dma_configure: Set if driver core should not configure DMA for this
+ *              device during probe.
  *
  * At the lowest level, every device in a Linux system is represented by an
  * instance of struct device. The device structure contains the information
@@ -965,6 +967,7 @@ struct device {
 	bool			offline_disabled:1;
 	bool			offline:1;
 	bool			of_node_reused:1;
+	bool			skip_dma_configure:1;
 };
 
 static inline struct device *kobj_to_dev(struct kobject *kobj)
-- 
2.13.3