On Friday 17 December 2004 1:51 am, Lothar Wassmann wrote:
> > xfer_size = ptd_xfer_size(ptd_q, xfer_type, len);
> > printk("len = %d, xfer_size = %d, mps = %d, xfer_type = %d\n",
> > len, xfer_size, mps, xfer_type);
> > if (xfer_size < len && xfer_size % mps) {
> > BUG_ON(xfer_size < mps);
> > // round down to an integer multiple of max_packet_size
> > xfer_size -= xfer_size % mps;
> >
> If xfer_size is less than mps this assignment would give a bogus
> result, thus the BUG_ON() macro to catch this case.
Not that I know that Philips chip or driver, but I don't see
why this should be a BUG either ... looks like the test is wrong,
the "if" should include "xfer_size > mps".
> > len = 64, xfer_size = 8, mps = 64, xfer_type = 3
> >
> It looks like your blocksize for the INT transfer buffer is set to 8
> and the device requires 64 byte max packet size.
If the endpoint descriptor says "at most 64 bytes", and
a read says "at most 8 bytes", that's perfectly legal.
If the device sends more data than the driver allowed
for, then the right thing to do is to return the data
the driver allowed for (with urb->actual_length == 8
in this case) AND report the standard buffer overflow
error.
> A data block of >
> max_packet_size byte is divided into an integral number of packets of
> max_packet_size byte plus one packet (the last one) that may carry
> less than max_packet_size byte of data. Thus the block size of each
> buffer area need to be at least 'max_packet_size' of the corresponding
> transfer type.
No it doesn't. It's perfectly reasonable for a driver
to know that the next IN transaction will be a short packet;
sometimes they even know the exact size. That "integral
number" can be zero (for buffers less than maxpacket).
- Dave
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