On Wed, 7 Apr 2010, David Ahern wrote: > I am looking at EHCI support for Qemu and noticing 20k data requests are > failing due to usbdevfs. It is limiting the max data request to 16k, > while the EHCI spec allows up to 20k (5 4k pages). This patch bumps the > max buffer size to 20k. This should not be done lightly. Since pages are allocated in powers of two, this will end up requiring 32 KB of contiguous memory -- which is not always that easy to come by. > the EHCI spec allows up to 20k This is ingenuous. The EHCI spec allows a single qTD to describe up to 20 KB of data. But that's not the limit on the size of a data request; bulk data transfers can be arbitrarily long. Qemu could solve its problem the same way libusb does: by breaking the large request up into multiple smaller requests. Alan Stern -- 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
