linux-kernel - [PATCH 1/3] sound: usb: line6: Replace mdelay with msleep in line6_read

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Date:   Sun, 18 Mar 2018 22:51:33 +0800
From:   Jia-Ju Bai <baijiaju1990@...il.com>
To:     perex@...ex.cz, tiwai@...e.com
Cc:     alsa-devel@...a-project.org, linux-kernel@...r.kernel.org,
        Jia-Ju Bai <baijiaju1990@...il.com>
Subject: [PATCH 1/3] sound: usb: line6: Replace mdelay with msleep in line6_read_data

line6_read_data() is never called in atomic context.

The call chains ending up at line6_read_data() are:
[1] line6_read_data() <- line6_read_serial_number() -> pod_startup4()
[2] line6_read_data() <- line6_read_serial_number() <- 
	podhd_startup_workqueue()
[3] line6_read_data() <- podhd_dev_start() <- podhd_startup_workqueue()
[4] line6_read_data() <- line6_read_serial_number() <- toneport_init()
	<- line6_probe()
[5] line6_read_data() <- toneport_init() <- line6_probe()

pod_startup4() and podhd_startup_workqueue() are set in INIT_WORK().
line6_probe() is called in toneport_probe(), pod_probe(), podhd_probe() 
and variax_probe(), which are set as ".probe" in usb_driver structure.
These functions are not called in atomic context.

Despite never getting called from atomic context, line6_read_data()
calls mdelay for busy wait.
That is not necessary and can be replaced with msleep to 
avoid busy waiting.

This is found by a static analysis tool named DCNS written by myself.

Signed-off-by: Jia-Ju Bai <baijiaju1990@...il.com>
---
 sound/usb/line6/driver.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/sound/usb/line6/driver.c b/sound/usb/line6/driver.c
index 0ff5a7d..af99e73 100644
--- a/sound/usb/line6/driver.c
+++ b/sound/usb/line6/driver.c
@@ -356,7 +356,7 @@ int line6_read_data(struct usb_line6 *line6, unsigned address, void *data,
 
 	/* Wait for data length. We'll get 0xff until length arrives. */
 	for (count = 0; count < LINE6_READ_WRITE_MAX_RETRIES; count++) {
-		mdelay(LINE6_READ_WRITE_STATUS_DELAY);
+		msleep(LINE6_READ_WRITE_STATUS_DELAY);
 
 		ret = usb_control_msg(usbdev, usb_rcvctrlpipe(usbdev, 0), 0x67,
 				      USB_TYPE_VENDOR | USB_RECIP_DEVICE |
-- 
1.9.1