Commit b44bbc46 authored Sep 13, 2016 by Roger Quadros Committed by Greg Kroah-Hartman Sep 13, 2016

usb: core: setup dma_pfn_offset for USB devices and, interfaces



If dma_pfn_offset is not inherited correctly from the host controller,
it might result in sub-optimal configuration as bounce
buffer limit might be set to less than optimal level.

Consider the mass storage device case.
USB storage driver creates a scsi host for the mass storage interface in
drivers/usb/storage/usb.c
The scsi host parent device is nothing but the the USB interface device.
Now, __scsi_init_queue() calls scsi_calculate_bounce_limit() to find out
and set the block layer bounce limit.
scsi_calculate_bounce_limit() uses dma_max_pfn(host_dev) to get the
bounce_limit. host_dev is nothing but the device representing the
mass storage interface.
If that device doesn't have the right dma_pfn_offset, then dma_max_pfn()
is messed up and the bounce buffer limit is wrong.

e.g. On Keystone 2 systems, dma_max_pfn() is 0x87FFFF and dma_mask_pfn
is 0xFFFFF. Consider a mass storage use case: Without this patch,
usb scsi host device (usb-storage) will get a dma_pfn_offset of 0 resulting
in a dma_max_pfn() of 0xFFFFF within the scsi layer
(scsi_calculate_bounce_limit()).
This will result in bounce buffers being unnecessarily used.

Hint: On 32-bit ARM platforms dma_max_pfn() = dma_mask_pfn + dma_pfn_offset

Signed-off-by: Roger Quadros <rogerq@ti.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

parent 9cdd8e11

drivers/usb/core/message.c

+5 −0

Original line number	Diff line number	Diff line
		@@ -1859,7 +1859,12 @@ free_interfaces:
		intf->dev.bus = &usb_bus_type;
		intf->dev.type = &usb_if_device_type;
		intf->dev.groups = usb_interface_groups;
		/*
		* Please refer to usb_alloc_dev() to see why we set
		* dma_mask and dma_pfn_offset.
		*/
		intf->dev.dma_mask = dev->dev.dma_mask;
		intf->dev.dma_pfn_offset = dev->dev.dma_pfn_offset;
		INIT_WORK(&intf->reset_ws, __usb_queue_reset_device);
		intf->minor = -1;
		device_initialize(&intf->dev);

drivers/usb/core/usb.c

+11 −0

Original line number	Diff line number	Diff line
		@@ -440,7 +440,18 @@ struct usb_device usb_alloc_dev(struct usb_device parent,
		dev->dev.bus = &usb_bus_type;
		dev->dev.type = &usb_device_type;
		dev->dev.groups = usb_device_groups;
		/*
		* Fake a dma_mask/offset for the USB device:
		* We cannot really use the dma-mapping API (dma_alloc_* and
		* dma_map_*) for USB devices but instead need to use
		* usb_alloc_coherent and pass data in 'urb's, but some subsystems
		* manually look into the mask/offset pair to determine whether
		* they need bounce buffers.
		* Note: calling dma_set_mask() on a USB device would set the
		* mask for the entire HCD, so don't do that.
		*/
		dev->dev.dma_mask = bus->controller->dma_mask;
		dev->dev.dma_pfn_offset = bus->controller->dma_pfn_offset;
		set_dev_node(&dev->dev, dev_to_node(bus->controller));
		dev->state = USB_STATE_ATTACHED;
		dev->lpm_disable_count = 1;

Admin message