On Wed, 26 Jun 2013, Ming Lei wrote:
> USB spec stats that short packet can only appear at the end
> of transfer. Because lost of HC(EHCI/UHCI/OHCI/...) can't
> build a full packet from discontinuous buffers, we introduce
> the limit in usb_submit_urb() to avoid such kind of bad sg buffers
> coming from driver.
>
> The limit might be a bit strict:
> - platform has iommu to do sg list mapping
> - some host controllers may support to build full packet from
> discontinuous buffers.
>
> But considered that most of HCs don't support that, and driver
> need work well or keep consistent on different HCs and ARCHs, we
> have to introduce the limit.
>
> Currently, only usbtest is reported to pass such sg buffers to HC,
> and other users(mass storage, usbfs) don't have the problem.
>
> We don't check it on USB wireless device, because:
> - wireless devices can't be attached to common USB
> bus(EHCI/UHCI/OHCI/...)
> - the max packet size of endpoint may be odd, and often can't
> devide 4KB which is a typical usage in usb mass storage application
> @@ -413,6 +414,16 @@ int usb_submit_urb(struct urb *urb, gfp_t mem_flags)
> urb->iso_frame_desc[n].status = -EXDEV;
> urb->iso_frame_desc[n].actual_length = 0;
> }
> + } else {
> + /* check sg buffer size */
> + if (dev->speed != USB_SPEED_WIRELESS && urb->num_sgs) {
> + struct scatterlist *sg;
> + int i;
Like Sergei said, you can save one level of indentation by converting
this to
}
/* check SG buffer sizes */
else if (dev->speed ...
Aside from that,
Acked-by: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>
Alan Stern
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