From 50aea6fca771d6daf3ec24f771da866f7fd836e4 Mon Sep 17 00:00:00 2001 From: Daniel Mack Date: Fri, 20 Jun 2014 00:20:44 +0200 Subject: [PATCH] usb: musb: cppi41: fire hrtimer according to programmed channel length The musb/cppi41 code installs a hrtimer to work around DMA completion interrupts that have fired too early on AM335x hardware. This timer is currently programmed to first fire 140 microseconds after the DMA completion callback. According to the commit which introduced it (a655f481d83, "usb: musb: musb_cppi41: handle pre-mature TX complete interrupt"), that value is is considered a 'rule of thumb' that worked well with the test case described in the commit log. Test show, however, that for USB audio devices and much smaller packet sizes, the timer has to fire earlier in order to correctly handle the audio stream. The original test case had output transfer sizes of 1514 bytes, and a delay of 140 microseconds. For audio devices with 24 bytes channel size, 3 microseconds seem to work well. Hence, let's assume that the time it takes to clear the bit correlates with the number of bytes transferred. The referenced commit log mentions such a suspicion as well. Let the timer fire in cppi41_channel->total_len/10 microseconds to correctly handle both cases. Also, shorten the interval in which the timer fires again in case of a non-empty early_tx list. With these changes in place, both FS and HS audio devices appear to work well on AM335x hardware. Signed-off-by: Daniel Mack Reported-by: Sebastian Reimers Signed-off-by: Felipe Balbi --- drivers/usb/musb/musb_cppi41.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/drivers/usb/musb/musb_cppi41.c b/drivers/usb/musb/musb_cppi41.c index a2c445608e75..adfffe884891 100644 --- a/drivers/usb/musb/musb_cppi41.c +++ b/drivers/usb/musb/musb_cppi41.c @@ -200,7 +200,7 @@ static enum hrtimer_restart cppi41_recheck_tx_req(struct hrtimer *timer) if (!list_empty(&controller->early_tx_list)) { ret = HRTIMER_RESTART; hrtimer_forward_now(&controller->early_tx, - ktime_set(0, 150 * NSEC_PER_USEC)); + ktime_set(0, 50 * NSEC_PER_USEC)); } spin_unlock_irqrestore(&musb->lock, flags); @@ -274,8 +274,10 @@ 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)) { + unsigned long usecs = cppi41_channel->total_len / 10; + hrtimer_start_range_ns(&controller->early_tx, - ktime_set(0, 140 * NSEC_PER_USEC), + ktime_set(0, usecs * NSEC_PER_USEC), 40 * NSEC_PER_USEC, HRTIMER_MODE_REL); } -- 2.30.2