xHCI: Fix TD Size calculation on 1.0 hosts.
commit 4525c0a10dff7ad3669763c28016c7daffc3900e upstream.
The xHCI 1.0 specification made a change to the TD Size field in TRBs.
The value is now the number of packets that remain to be sent in the TD,
not including this TRB. The TD Size value for the last TRB in a TD must
always be zero.
The xHCI function xhci_v1_0_td_remainder() attempts to calculate this,
but it gets it wrong. First, it erroneously reuses the old
xhci_td_remainder function, which will right shift the value by 10. The
xHCI 1.0 spec as of June 2011 says nothing about right shifting by 10.
Second, it does not set the TD size for the last TRB in a TD to zero.
Third, it uses roundup instead of DIV_ROUND_UP. The total packet count
is supposed to be the total number of bytes in this TD, divided by the
max packet size, rounded up. DIV_ROUND_UP is the right function to use
in that case.
With the old code, a TD on an endpoint with max packet size 1024 would
be set up like so:
TRB 1, TRB length = 600 bytes, TD size = 0
TRB 1, TRB length = 200 bytes, TD size = 0
TRB 1, TRB length = 100 bytes, TD size = 0
With the new code, the TD would be set up like this:
TRB 1, TRB length = 600 bytes, TD size = 1
TRB 1, TRB length = 200 bytes, TD size = 1
TRB 1, TRB length = 100 bytes, TD size = 0
This commit should be backported to kernels as old as 3.0, that contain
the commit 4da6e6f247a2601ab9f1e63424e4d944ed4124f3 "xhci 1.0: Update TD
size field format."
Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>
Reported-by: Chintan Mehta <chintan.mehta@sibridgetech.com>
Reported-by: Shimmer Huang <shimmering.h@gmail.com>
Tested-by: Bhavik Kothari <bhavik.kothari@sibridgetech.com>
Tested-by: Shimmer Huang <shimmering.h@gmail.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
1 file changed
