This is a note to let you know that I've just added the patch titled
usb: musb: Ensure that cppi41 timer gets armed on premature DMA TX irq
to the 3.15-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
usb-musb-ensure-that-cppi41-timer-gets-armed-on-premature-dma-tx-irq.patch
and it can be found in the queue-3.15 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From c58d80f523ffc15ef4d062fc7aeb03793fe39701 Mon Sep 17 00:00:00 2001
From: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Date: Fri, 20 Jun 2014 23:41:24 +0200
Subject: usb: musb: Ensure that cppi41 timer gets armed on premature DMA TX irq
From: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
commit c58d80f523ffc15ef4d062fc7aeb03793fe39701 upstream.
Some TI chips raise the DMA complete interrupt before the actual
transfer has been completed. The code tries to busy wait for a few
microseconds and if that fails it arms an hrtimer to recheck. So far
so good, but that has the following issue:
CPU 0 CPU1
start_next_transfer(RQ1);
DMA interrupt
if (premature_irq(RQ1))
if (!hrtimer_active(timer))
hrtimer_start(timer);
hrtimer expires
timer->state = CALLBACK_RUNNING;
timer->fn()
cppi41_recheck_tx_req()
complete_request(RQ1);
if (requests_pending())
start_next_transfer(RQ2);
DMA interrupt
if (premature_irq(RQ2))
if (!hrtimer_active(timer))
hrtimer_start(timer);
timer->state = INACTIVE;
The premature interrupt of request2 on CPU1 does not arm the timer and
therefor the request completion never happens because it checks for
!hrtimer_active(). hrtimer_active() evaluates:
timer->state != HRTIMER_STATE_INACTIVE
which of course evaluates to true in the above case as timer->state is
CALLBACK_RUNNING.
That's clearly documented:
* A timer is active, when it is enqueued into the rbtree or the
* callback function is running or it's in the state of being migrated
* to another cpu.
But that's not what the code wants to check. The code wants to check
whether the timer is queued, i.e. whether its armed and waiting for
expiry.
We have a helper function for this: hrtimer_is_queued(). This
evaluates:
timer->state & HRTIMER_STATE_QUEUED
So in the above case this evaluates to false and therefor forces the
DMA interrupt on CPU1 to call hrtimer_start().
Use hrtimer_is_queued() instead of hrtimer_active() and evrything is
good.
Reported-by: Torben Hohn <torbenh@xxxxxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Felipe Balbi <balbi@xxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/usb/musb/musb_cppi41.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--- a/drivers/usb/musb/musb_cppi41.c
+++ b/drivers/usb/musb/musb_cppi41.c
@@ -318,7 +318,7 @@ static void cppi41_dma_callback(void *pr
}
list_add_tail(&cppi41_channel->tx_check,
&controller->early_tx_list);
- if (!hrtimer_active(&controller->early_tx)) {
+ if (!hrtimer_is_queued(&controller->early_tx)) {
hrtimer_start_range_ns(&controller->early_tx,
ktime_set(0, 140 * NSEC_PER_USEC),
40 * NSEC_PER_USEC,
Patches currently in stable-queue which might be from tglx@xxxxxxxxxxxxx are
queue-3.15/usb-musb-ensure-that-cppi41-timer-gets-armed-on-premature-dma-tx-irq.patch
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