linux-stable.git/drivers/usb/host/ehci-timer.c, branch linux-3.9.y

USB: EHCI: fix regression in QH unlinking

2013-03-20T23:17:22+00:00

This patch (as1670) fixes a regression caused by commit
6402c796d3b4205d3d7296157956c5100a05d7d6 (USB: EHCI: work around
silicon bug in Intel's EHCI controllers).  The workaround goes through
two IAA cycles for each QH being unlinked.  During the first cycle,
the QH is not added to the async_iaa list (because it isn't fully gone
from the hardware yet), which means that list will be empty.

Unfortunately, I forgot to update the IAA watchdog timer routine.  It
thinks that an empty async_iaa list means the timer expiration was an
error, which isn't true any more.  This problem didn't show up during
initial testing because the controllers being tested all had working
IAA interrupts.  But not all controllers do, and when the watchdog
timer expires, the empty-list check prevents the second IAA cycle from
starting.  As a result, URB unlinks never complete.  The check needs
to be removed.

Among the symptoms of the regression are processes stuck in D wait
states and hangs during system shutdown.

Signed-off-by: Alan Stern 
Reported-and-tested-by: Stephen Warren 
Reported-and-tested-by: Sven Joachim 
Reported-by: Andreas Bombe 
Cc: stable 
Signed-off-by: Greg Kroah-Hartman

USB: EHCI: revert "remove ASS/PSS polling timeout"

2013-02-26T21:22:38+00:00

This patch (as1649) reverts commit
55bcdce8a8228223ec4d17d8ded8134ed265d2c5 (USB: EHCI: remove ASS/PSS
polling timeout).  That commit was written under the assumption that
some controllers may take a very long time to turn off their async and
periodic schedules.  It now appears that in fact the schedules do get
turned off reasonably quickly, but some controllers occasionally leave
the schedules' status bits turned on and consequently ehci-hcd can't
tell that the schedules are off.

VIA controllers in particular have this problem.  ehci-hcd tells the
hardware to turn off the async schedule, the schedule does get turned
off, but the status bit remains on.  Since the EHCI spec requires that
the schedules not be re-enabled until the previous disable has taken
effect, with an unlimited timeout the async schedule never gets turned
back on.  The resulting symptom is that the system is unable to
communicate with USB devices.

Signed-off-by: Alan Stern 
Reported-and-tested-by: Ronald 
Reported-and-tested-by: Paul Hartman 
Reported-and-tested-by: Dieter Nützel 
Reported-and-tested-by: Jean Delvare 
Cc: stable 
Signed-off-by: Greg Kroah-Hartman

USB: EHCI: remove ASS/PSS polling timeout

2013-01-25T21:58:20+00:00

This patch (as1647) attempts to work around a problem that seems to
affect some nVidia EHCI controllers.  They sometimes take a very long
time to turn off their async or periodic schedules.  I don't know if
this is a result of other problems, but in any case it seems wise not
to depend on schedule enables or disables taking effect in any
specific length of time.

The patch removes the existing 20-ms timeout for enabling and
disabling the schedules.  The driver will now continue to poll the
schedule state at 1-ms intervals until the controller finally decides
to obey the most recent command issued by the driver.  Just in case
this hides a problem, a debugging message will be logged if the
controller takes longer than 20 polls.

I don't know if this will actually fix anything, but it can't hurt.

Signed-off-by: Alan Stern 
Tested-by: Piergiorgio Sartor 
CC: 
Signed-off-by: Greg Kroah-Hartman

USB: EHCI: convert warning messages to debug-level

2012-09-21T16:37:53+00:00

This patch (as1606) converts two warning messages in the ehci-hcd
driver to debug messages, and adds a little extra information to each.

The log messages occur when an EHCI controller takes too long (more
than 20 ms) to turn its async or periodic schedule on or off.  If this
happens at all, it's liable to happen quite often and there's no point
spamming the system log with these warnings.  Furthermore, there's
nothing much we can do about it when the problem happens.

Signed-off-by: Alan Stern 
Reported-and-tested-by: Thomas Voegtle 
Cc: stable  # [3.6]
Signed-off-by: Greg Kroah-Hartman

USB: EHCI: use hrtimer for the I/O watchdog

2012-07-16T23:56:47+00:00

This patch (as1586) replaces the kernel timer used by ehci-hcd as an
I/O watchdog with an hrtimer event.

Unlike in the current code, the watchdog event is now always enabled
whenever any isochronous URBs are active.  This will prevent bugs
caused by the periodic schedule wrapping around with no completion
interrupts; the watchdog handler is guaranteed to scan the isochronous
transfers at least once during each iteration of the schedule.  The
extra overhead will be negligible: one timer interrupt every 100 ms.

Signed-off-by: Alan Stern 
Signed-off-by: Greg Kroah-Hartman

USB: EHCI: always scan each interrupt QH

2012-07-16T23:56:47+00:00

This patch (as1585) fixes a bug in ehci-hcd's scheme for scanning
interrupt QHs.

Currently a single routine takes care of scanning everything on the
periodic schedule.  Whenever an interrupt occurs, it scans all
isochronous and interrupt URBs scheduled for frames that have elapsed
since the last scan.

This has two disadvantages.  The first is relatively minor: An
interrupt QH is likely to end up getting scanned multiple times,
particularly if the last scan was not fairly recent.  (The current
code avoids this by maintaining a periodic_stamp in each interrupt
QH.)

The second is more serious.  The periodic schedule wraps around.  If
the last scan occurred during frame N, and the next scan occurs when
the schedule has gone through an entire cycle and is back at frame N,
the scanning code won't look at any frames other than N.  Consequently
it won't see any QHs that completed during frame N-1 or earlier.

The patch replaces the entire frame-based approach for scanning
interrupt QHs with a new routine using a list-based approach, the same
as for async QHs.  This has a slight disadvantage, because it means
that all interrupt QHs have to be scanned every time.  But it is more
robust than the current approach.

Signed-off-by: Alan Stern 
Signed-off-by: Greg Kroah-Hartman

USB: EHCI: use hrtimer for unlinking empty async QHs

2012-07-16T23:56:47+00:00

This patch (as1583) changes ehci-hcd to use an hrtimer event for
unlinking empty (unused) async QHs instead of using a kernel timer.

The check for empty QHs is moved to a new routine, where it doesn't
require going through an entire scan of both the async and periodic
schedules.  And it can unlink multiple QHs at once, unlike the current
code.

Signed-off-by: Alan Stern 
Signed-off-by: Greg Kroah-Hartman

USB: EHCI: unlink multiple async QHs together

2012-07-16T23:56:47+00:00

This patch (as1582) changes ehci-hcd's strategy for unlinking async
QHs.  Currently the driver never unlinks more than one QH at a time.
This can be inefficient and cause unnecessary delays, since a QH
cannot be reused while it is waiting to be unlinked.

The new strategy unlinks all the waiting QHs at once.  In practice the
improvement won't be very big, because it's somewhat uncommon to have
two or more QHs waiting to be unlinked at any time.  But it does
happen, and in any case, doing things this way makes more sense IMO.

The change requires the async unlinking code to be refactored
slightly.  Now in addition to the routines for starting and ending an
unlink, there are new routines for unlinking a single QH and starting
an IAA cycle.  This approach is needed because there are two separate
paths for unlinking async QHs:

	When a transfer error occurs or an URB is cancelled, the QH
	must be unlinked right away;

	When a QH has been idle sufficiently long, it is unlinked
	to avoid consuming DMA bandwidth uselessly.

In the first case we want the unlink to proceed as quickly as
possible, whereas in the second case we can afford to batch several
QHs together and unlink them all at once.  Hence the division of
labor.

Signed-off-by: Alan Stern 
Signed-off-by: Greg Kroah-Hartman

USB: EHCI: use hrtimer for the IAA watchdog

2012-07-16T23:56:46+00:00

This patch (as1581) replaces the iaa_watchdog kernel timer used by
ehci-hcd with an hrtimer event, in keeping with the general conversion
to high-res timers.

Signed-off-by: Alan Stern 
Signed-off-by: Greg Kroah-Hartman

USB: EHCI: use hrtimer for (s)iTD deallocation

2012-07-16T23:54:25+00:00

This patch (as1579) adds an hrtimer event to handle deallocation of
iTDs and siTDs in ehci-hcd.

Because of the frame-oriented approach used by the EHCI periodic
schedule, the hardware can continue to access the Transfer Descriptor
for isochronous (or split-isochronous) transactions for up to a
millisecond after the transaction completes.  The iTD (or siTD) must
not be reused before then.

The strategy currently used involves putting completed iTDs on a list
of cached entries and every so often returning them to the endpoint's
free list.  The new strategy reduces overhead by putting completed
iTDs back on the free list immediately, although they are not reused
until it is safe to do so.

When the isochronous endpoint stops (its queue becomes empty), the
iTDs on its free list get moved to a global list, from which they will
be deallocated after a minimum of 2 ms.  This delay is what the new
hrtimer event is for.

Overall this may not be a tremendous improvement over the current
code, but to me it seems a lot more clear and logical.  In addition,
it removes the need for each iTD to keep a reference to the
ehci_iso_stream it belongs to, since the iTD never needs to be moved
back to the stream's free list from the global list.

Signed-off-by: Alan Stern 
Signed-off-by: Greg Kroah-Hartman