serial: replace open coded mutex with a real mutex in mrst_max3110.c

The mrst_max3110.c driver uses an open coded, non atomic variable
to create exclusion between two of its worker threads. More than that,
while the main thread does a proper set-work-clear sequence,
the other thread only does a test, with the result that no actual
exclusion is happening.

this patch replaces this open coded variable with a proper mutex

in addition, the 'lock' spinlock is removed from the per adapter structure,
the lock was only ever initialized but never used

Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 8 insertions, 7 deletions

diff --git a/drivers/serial/mrst_max3110.c b/drivers/serial/mrst_max3110.c
index f9c01aeb6f80..0341853e0c28 100644
--- a/drivers/serial/mrst_max3110.c
+++ b/drivers/serial/mrst_max3110.c
@@ -56,8 +56,7 @@ struct uart_max3110 {
         wait_queue_head_t wq;
         struct task_struct *main_thread;
         struct task_struct *read_thread;
-        int mthread_up;
-        spinlock_t lock;
+        struct mutex thread_mutex;;
 
         u32 baud;
         u16 cur_conf;
@@ -397,7 +396,8 @@ static int max3110_main_thread(void *_max)
                                                atomic_read(&max->con_tx_need) ||
                                              atomic_read(&max->uart_tx_need)) ||
                                              kthread_should_stop());
-                max->mthread_up = 1;
+
+                mutex_lock(&max->thread_mutex);
 
 #ifdef CONFIG_MRST_MAX3110_IRQ
                 if (atomic_read(&max->irq_pending)) {
@@ -417,7 +417,7 @@ static int max3110_main_thread(void *_max)
                         transmit_char(max);
                         atomic_set(&max->uart_tx_need, 0);
                 }
-                max->mthread_up = 0;
+                mutex_unlock(&max->thread_mutex);
         } while (!kthread_should_stop());
 
         return ret;
@@ -444,8 +444,9 @@ static int max3110_read_thread(void *_max)
 
         pr_info(PR_FMT "start read thread\n");
         do {
-                if (!max->mthread_up)
-                        max3110_console_receive(max);
+                mutex_lock(&max->thread_mutex);
+                max3110_console_receive(max);
+                mutex_unlock(&max->thread_mutex);
 
                 set_current_state(TASK_INTERRUPTIBLE);
                 schedule_timeout(HZ / 20);
@@ -745,7 +746,7 @@ static int serial_m3110_probe(struct spi_device *spi)
         max->name = spi->modalias;      /* use spi name as the name */
         max->irq = (u16)spi->irq;
 
-        spin_lock_init(&max->lock);
+        mutex_init(&max->thread_mutex);
 
         max->word_7bits = 0;
         max->parity = 0;