MN10300: ttySM: Use memory barriers correctly in circular buffer logic

Use memory barriers correctly in the circular buffer logic used in the driver,
as documented in Documentation/circular-buffers.txt.

Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Mark Salter <msalter@redhat.com>

1 files changed, 8 insertions, 6 deletions

diff --git a/arch/mn10300/kernel/mn10300-serial.c b/arch/mn10300/kernel/mn10300-serial.c
index 339cef4c8256..131b81f9d6c8 100644
--- a/arch/mn10300/kernel/mn10300-serial.c
+++ b/arch/mn10300/kernel/mn10300-serial.c
@@ -487,16 +487,17 @@ static void mn10300_serial_receive_interrupt(struct mn10300_serial_port *port)
 
 try_again:
         /* pull chars out of the hat */
-        ix = port->rx_outp;
-        if (ix == port->rx_inp) {
+        ix = ACCESS_ONCE(port->rx_outp);
+        if (CIRC_CNT(port->rx_inp, ix, MNSC_BUFFER_SIZE) == 0) {
                 if (push && !tty->low_latency)
                         tty_flip_buffer_push(tty);
                 return;
         }
 
+        smp_read_barrier_depends();
         ch = port->rx_buffer[ix++];
         st = port->rx_buffer[ix++];
-        smp_rmb();
+        smp_mb();
         port->rx_outp = ix & (MNSC_BUFFER_SIZE - 1);
         port->uart.icount.rx++;
 
@@ -1657,13 +1658,14 @@ static int mn10300_serial_poll_get_char(struct uart_port *_port)
 
         do {
                 /* pull chars out of the hat */
-                ix = port->rx_outp;
-                if (ix == port->rx_inp)
+                ix = ACCESS_ONCE(port->rx_outp);
+                if (CIRC_CNT(port->rx_inp, ix, MNSC_BUFFER_SIZE) == 0)
                         return NO_POLL_CHAR;
 
+                smp_read_barrier_depends();
                 ch = port->rx_buffer[ix++];
                 st = port->rx_buffer[ix++];
-                smp_rmb();
+                smp_mb();
                 port->rx_outp = ix & (MNSC_BUFFER_SIZE - 1);
 
         } while (st & (SC01STR_FEF | SC01STR_PEF | SC01STR_OEF));