firewire: ohci: always use packet-per-buffer mode for isochronous reception
This is a minimal change meant for the short term: Never set the
ohci->use_dualbuffer flag to true.
There are two reasons to do so:
- Packet-per-buffer mode and dual-buffer mode do not behave the same
under certain circumstances, notably if several packets are covered
by a single fw_cdev_iso_packet descriptor.
http://marc.info/?l=linux1394-devel&m=124965653718313
Therefore the driver stack should not silently choose one or the
other mode but should leave the choice to the high-level driver
(regardless if kernel driver or userspace driver). Or simply always
only offer packet-per-buffer mode, since a considerable number of
controllers, even current ones, does not offer dual-buffer support.
- Even under circumstances where packet-per-buffer mode and
dual-buffer mode behave exactly the same --- notably when used
through libraw1394, libdc1394, as well as the current two kernel
drivers which use isochronous reception (firewire-net and firedtv)
--- we are still faced with the problem that several OHCI 1.1
controllers have bugs in dual-buffer mode. Although it looks like
we have identified most of those buggy controllers by now, we
cannot be quite sure about that.
So, use packet-per-buffer by default from now on. This change should
be followed up by a more complete solution: Either extend the
in-kernel API and the userspace ABI by a choice between the two IR modes
or remove all dual-buffer related code from firewire-ohci.
Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>
diff --git a/drivers/firewire/ohci.c b/drivers/firewire/ohci.c
index 96768e1..a61571c 100644
--- a/drivers/firewire/ohci.c
+++ b/drivers/firewire/ohci.c
@@ -2226,7 +2226,6 @@
if (rest == 0)
return -EINVAL;
- /* FIXME: make packet-per-buffer/dual-buffer a context option */
while (rest > 0) {
d = context_get_descriptors(&ctx->context,
z + header_z, &d_bus);
@@ -2470,7 +2469,10 @@
}
version = reg_read(ohci, OHCI1394_Version) & 0x00ff00ff;
+#if 0
+ /* FIXME: make it a context option or remove dual-buffer mode */
ohci->use_dualbuffer = version >= OHCI_VERSION_1_1;
+#endif
/* dual-buffer mode is broken if more than one IR context is active */
if (dev->vendor == PCI_VENDOR_ID_AGERE &&