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@xxxxxx> --- Changelog: v3: - removed comments from code as commit log is sufficient. v2: - added more information in commit log and code. drivers/usb/core/message.c | 1 + drivers/usb/core/usb.c | 1 + 2 files changed, 2 insertions(+) diff --git a/drivers/usb/core/message.c b/drivers/usb/core/message.c index 0406a59..6856b7a 100644 --- a/drivers/usb/core/message.c +++ b/drivers/usb/core/message.c @@ -1863,6 +1863,7 @@ free_interfaces: intf->dev.type = &usb_if_device_type; intf->dev.groups = usb_interface_groups; 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); diff --git a/drivers/usb/core/usb.c b/drivers/usb/core/usb.c index 5e80697..d81791a 100644 --- a/drivers/usb/core/usb.c +++ b/drivers/usb/core/usb.c @@ -441,6 +441,7 @@ struct usb_device *usb_alloc_dev(struct usb_device *parent, dev->dev.type = &usb_device_type; dev->dev.groups = usb_device_groups; 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; -- 2.7.4 -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
