serial: 8250: Create serial_lsr_in()

LSR register readers need to be careful in order to not lose bits that
are not preserved across reads. Create a helper that takes care of
storing the non-preserved bits into lsr_save_flags.

Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Link: https://lore.kernel.org/r/20220608095431.18376-3-ilpo.jarvinen@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/serial/8250/8250.h b/drivers/tty/serial/8250/8250.h
index 696030c..c89cb88 100644 (file)
--- a/drivers/tty/serial/8250/8250.h
+++ b/drivers/tty/serial/8250/8250.h
@@ -123,6 +123,26 @@ static inline void serial_out(struct uart_8250_port *up, int offset, int value)
        up->port.serial_out(&up->port, offset, value);
 }
 
+/**
+ *     serial_lsr_in - Read LSR register and preserve flags across reads
+ *     @up:    uart 8250 port
+ *
+ *     Read LSR register and handle saving non-preserved flags across reads.
+ *     The flags that are not preserved across reads are stored into
+ *     up->lsr_saved_flags.
+ *
+ *     Returns LSR value or'ed with the preserved flags (if any).
+ */
+static inline unsigned int serial_lsr_in(struct uart_8250_port *up)
+{
+       unsigned int lsr = up->lsr_saved_flags;
+
+       lsr |= serial_in(up, UART_LSR);
+       up->lsr_saved_flags = lsr & LSR_SAVE_FLAGS;
+
+       return lsr;
+}
+
 /*
  * For the 16C950
  */

diff --git a/drivers/tty/serial/8250/8250_core.c b/drivers/tty/serial/8250/8250_core.c
index cfbd2de..b0320de 100644 (file)
--- a/drivers/tty/serial/8250/8250_core.c
+++ b/drivers/tty/serial/8250/8250_core.c
@@ -276,8 +276,7 @@ static void serial8250_backup_timeout(struct timer_list *t)
         * the "Diva" UART used on the management processor on many HP
         * ia64 and parisc boxes.
         */
-       lsr = serial_in(up, UART_LSR);
-       up->lsr_saved_flags |= lsr & LSR_SAVE_FLAGS;
+       lsr = serial_lsr_in(up);
        if ((iir & UART_IIR_NO_INT) && (up->ier & UART_IER_THRI) &&
            (!uart_circ_empty(&up->port.state->xmit) || up->port.x_char) &&
            (lsr & UART_LSR_THRE)) {

diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
index 209ecb1..5a5e81d 100644 (file)
--- a/drivers/tty/serial/8250/8250_port.c
+++ b/drivers/tty/serial/8250/8250_port.c
@@ -1508,11 +1508,9 @@ static inline void __stop_tx(struct uart_8250_port *p)
        struct uart_8250_em485 *em485 = p->em485;
 
        if (em485) {
-               unsigned char lsr = serial_in(p, UART_LSR);
+               unsigned char lsr = serial_lsr_in(p);
                u64 stop_delay = 0;
 
-               p->lsr_saved_flags |= lsr & LSR_SAVE_FLAGS;
-
                if (!(lsr & UART_LSR_THRE))
                        return;
                /*
@@ -1569,10 +1567,8 @@ static inline void __start_tx(struct uart_port *port)
 
        if (serial8250_set_THRI(up)) {
                if (up->bugs & UART_BUG_TXEN) {
-                       unsigned char lsr;
+                       unsigned char lsr = serial_lsr_in(up);
 
-                       lsr = serial_in(up, UART_LSR);
-                       up->lsr_saved_flags |= lsr & LSR_SAVE_FLAGS;
                        if (lsr & UART_LSR_THRE)
                                serial8250_tx_chars(up);
                }
@@ -2002,8 +1998,7 @@ static unsigned int serial8250_tx_empty(struct uart_port *port)
        serial8250_rpm_get(up);
 
        spin_lock_irqsave(&port->lock, flags);
-       lsr = serial_port_in(port, UART_LSR);
-       up->lsr_saved_flags |= lsr & LSR_SAVE_FLAGS;
+       lsr = serial_lsr_in(up);
        spin_unlock_irqrestore(&port->lock, flags);
 
        serial8250_rpm_put(up);
@@ -2079,9 +2074,7 @@ static void wait_for_lsr(struct uart_8250_port *up, int bits)
 
        /* Wait up to 10ms for the character(s) to be sent. */
        for (;;) {
-               status = serial_in(up, UART_LSR);
-
-               up->lsr_saved_flags |= status & LSR_SAVE_FLAGS;
+               status = serial_lsr_in(up);
 
                if ((status & bits) == bits)
                        break;