From c58d80f523ffc15ef4d062fc7aeb03793fe39701 Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Fri, 20 Jun 2014 23:41:24 +0200 Subject: [PATCH] usb: musb: Ensure that cppi41 timer gets armed on premature DMA TX irq 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 Signed-off-by: Thomas Gleixner Cc: stable@vger.kernel.org Signed-off-by: Felipe Balbi --- 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 7b8bbf53127e..5341bb223b7c 100644 --- a/drivers/usb/musb/musb_cppi41.c +++ b/drivers/usb/musb/musb_cppi41.c @@ -318,7 +318,7 @@ 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, -- 2.20.1