From b44bbc46a8bbcd9c6bb1d167ca3f78d3aa5ee41d Mon Sep 17 00:00:00 2001 From: Roger Quadros Date: Tue, 13 Sep 2016 11:16:03 +0300 Subject: 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 Acked-by: Arnd Bergmann Acked-by: Alan Stern Signed-off-by: Greg Kroah-Hartman --- drivers/usb/core/message.c | 5 +++++ 1 file changed, 5 insertions(+) (limited to 'drivers/usb/core/message.c') diff --git a/drivers/usb/core/message.c b/drivers/usb/core/message.c index 5ab5c1a81462..3a4707746157 100644 --- a/drivers/usb/core/message.c +++ b/drivers/usb/core/message.c @@ -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); -- cgit v1.2.3