mfd: kempld-core: Fix potential hang-up during boot

On PXT and COMe-cPC2 boards it is observed that the hardware
mutex is acquired but not being released during initialization.
This can result in a hang-up during boot if the driver is built
into the kernel.

Releasing the mutex twice if it was acquired fixes the problem.
Subsequent request/release cycles work as expected, so the fix is
only needed during initialization.

Cc: <stable@vger.kernel.org>
Reviewed-by: Michael Brunner <michael.brunner@kontron.com>
Tested-by: Michael Brunner <michael.brunner@kontron.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

1 files changed, 5 insertions, 2 deletions

diff --git a/drivers/mfd/kempld-core.c b/drivers/mfd/kempld-core.c
index 20a6afcfb36c..07692604e119 100644
--- a/drivers/mfd/kempld-core.c
+++ b/drivers/mfd/kempld-core.c
@@ -322,9 +322,12 @@ static int kempld_detect_device(struct kempld_device_data *pld)
                 return -ENODEV;
         }
 
-        /* Release hardware mutex if aquired */
-        if (!(index_reg & KEMPLD_MUTEX_KEY))
+        /* Release hardware mutex if acquired */
+        if (!(index_reg & KEMPLD_MUTEX_KEY)) {
                 iowrite8(KEMPLD_MUTEX_KEY, pld->io_index);
+                /* PXT and COMe-cPC2 boards may require a second release */
+                iowrite8(KEMPLD_MUTEX_KEY, pld->io_index);
+        }
 
         mutex_unlock(&pld->lock);