Hi Alan, On 12/09/16 16:09, Alan Stern wrote: > On Mon, 12 Sep 2016, Roger Quadros wrote: > >> 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> >> --- > > How does v2 of this patch differ from v1? No functional difference. Just added more explanation in the commit log. > >> drivers/usb/core/message.c | 6 ++++++ >> drivers/usb/core/usb.c | 7 +++++++ >> 2 files changed, 13 insertions(+) >> >> diff --git a/drivers/usb/core/message.c b/drivers/usb/core/message.c >> index 0406a59..66364ea 100644 >> --- a/drivers/usb/core/message.c >> +++ b/drivers/usb/core/message.c >> @@ -1863,6 +1863,12 @@ free_interfaces: >> intf->dev.type = &usb_if_device_type; >> intf->dev.groups = usb_interface_groups; >> intf->dev.dma_mask = dev->dev.dma_mask; >> + /* Propagate dma_pfn_offset to USB interface. >> + * This is especially required by mass storage interface >> + * which relies on SCSI layer and scsi_calculate_bounce_limit() >> + * to set the bounce buffer limit based on dma_pfn_offset. >> + */ >> + intf->dev.dma_pfn_offset = dev->dev.dma_pfn_offset; > > I really think this comment isn't necessary. It seems pretty obvious > that if you're copying DMA-related fields from one device to another > then you'll want to copy the dma_pfn_offset along with everything else. > No? > > The explanation in the Changelog is enough, IMO. Fine with me. > >> 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..7dde93d 100644 >> --- a/drivers/usb/core/usb.c >> +++ b/drivers/usb/core/usb.c >> @@ -441,6 +441,13 @@ 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; >> + /* Propagate bus controller's dma_pfn_offset to USB device, >> + * as it would be needed to be propagated to USB interfaces. >> + * This is especially required by mass storage interface >> + * which relies on SCSI layer and scsi_calculate_bounce_limit() >> + * to set the bounce buffer limit based on dma_pfn_offset. >> + */ >> + dev->dev.dma_pfn_offset = bus->controller->dma_pfn_offset; > > Same here. OK. > >> set_dev_node(&dev->dev, dev_to_node(bus->controller)); >> dev->state = USB_STATE_ATTACHED; >> dev->lpm_disable_count = 1; > > Alan Stern > cheers, -roger -- 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
