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 <rog...@ti.com> > ---
How does v2 of this patch differ from v1? > 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. > 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. > set_dev_node(&dev->dev, dev_to_node(bus->controller)); > dev->state = USB_STATE_ATTACHED; > dev->lpm_disable_count = 1; Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
