watchdog: dw_wdt: No need for a spinlock

Right now the dw_wdt uses a spinlock to protect dw_wdt_open().  The
problem is that while holding the spinlock we call:
-> dw_wdt_set_top()
   -> dw_wdt_top_in_seconds()
      -> clk_get_rate()
         -> clk_prepare_lock()
            -> mutex_lock()

Locking a mutex while holding a spinlock is not allowed and leads to
warnings like "BUG: spinlock wrong CPU on CPU#1", among other
problems.

There's no reason to use a spinlock.  Only dw_wdt_open() was protected
and the test_and_set_bit() at the start of that function protects us
anyway.

Signed-off-by: Doug Anderson <dianders@chromium.org>
Tested-by: Jisheng Zhang <jszhang@marvell.com>
Reviewed-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>

diff --git a/drivers/watchdog/dw_wdt.c b/drivers/watchdog/dw_wdt.c
index d0bb9499d12caaa2d901b3454a0c65cf825a9ea4..a284abdb4fb61a82a743f8a0d192636f94dbee83 100644 (file)
--- a/drivers/watchdog/dw_wdt.c
+++ b/drivers/watchdog/dw_wdt.c
@@ -35,7 +35,6 @@
 #include <linux/pm.h>
 #include <linux/platform_device.h>
 #include <linux/reboot.h>
-#include <linux/spinlock.h>
 #include <linux/timer.h>
 #include <linux/uaccess.h>
 #include <linux/watchdog.h>
@@ -61,7 +60,6 @@ MODULE_PARM_DESC(nowayout, "Watchdog cannot be stopped once started "
 #define WDT_TIMEOUT            (HZ / 2)
 
 static struct {
-       spinlock_t              lock;
        void __iomem            *regs;
        struct clk              *clk;
        unsigned long           in_use;
@@ -177,7 +175,6 @@ static int dw_wdt_open(struct inode *inode, struct file *filp)
        /* Make sure we don't get unloaded. */
        __module_get(THIS_MODULE);
 
-       spin_lock(&dw_wdt.lock);
        if (!dw_wdt_is_enabled()) {
                /*
                 * The watchdog is not currently enabled. Set the timeout to
@@ -190,8 +187,6 @@ static int dw_wdt_open(struct inode *inode, struct file *filp)
 
        dw_wdt_set_next_heartbeat();
 
-       spin_unlock(&dw_wdt.lock);
-
        return nonseekable_open(inode, filp);
 }
 
@@ -348,8 +343,6 @@ static int dw_wdt_drv_probe(struct platform_device *pdev)
        if (ret)
                return ret;
 
-       spin_lock_init(&dw_wdt.lock);
-
        ret = misc_register(&dw_wdt_miscdev);
        if (ret)
                goto out_disable_clk;