[3.13.y.z extended stable] Patch "usb: musb: Ensure that cppi41 timer gets armed on premature DMA TX irq" has been added to staging queue
Kamal Mostafa
kamal at canonical.com
Wed Aug 6 20:54:15 UTC 2014
This is a note to let you know that I have just added a patch titled
usb: musb: Ensure that cppi41 timer gets armed on premature DMA TX irq
to the linux-3.13.y-queue branch of the 3.13.y.z extended stable tree
which can be found at:
http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.13.y-queue
This patch is scheduled to be released in version 3.13.11.6.
If you, or anyone else, feels it should not be added to this tree, please
reply to this email.
For more information about the 3.13.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable
Thanks.
-Kamal
------
>From 99b9d38ddcc0ee176175629dc9261a2eca4b687c Mon Sep 17 00:00:00 2001
From: Thomas Gleixner <tglx at linutronix.de>
Date: Fri, 20 Jun 2014 23:41:24 +0200
Subject: usb: musb: Ensure that cppi41 timer gets armed on premature DMA TX
irq
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 at linutronix.de>
Signed-off-by: Thomas Gleixner <tglx at linutronix.de>
Signed-off-by: Felipe Balbi <balbi at ti.com>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
drivers/usb/musb/musb_cppi41.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/usb/musb/musb_cppi41.c b/drivers/usb/musb/musb_cppi41.c
index a12bd30..4a5af5c 100644
--- a/drivers/usb/musb/musb_cppi41.c
+++ b/drivers/usb/musb/musb_cppi41.c
@@ -266,7 +266,7 @@ static void cppi41_dma_callback(void *private_data)
}
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,
--
1.9.1
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