[PATCH 5.19 0899/1157] serial: 8250: Create serial_lsr_in()

Greg Kroah-Hartman
2022-08-16T00:42:22Z

From: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>

[ Upstream commit bdb70c424df1543bc02ee2639aecebd20318c599 ]

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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/tty/serial/8250/8250.h | 20 ++++++++++++++++++++
drivers/tty/serial/8250/8250_core.c | 3 +--
drivers/tty/serial/8250/8250_port.c | 15 ++++-----------
3 files changed, 25 insertions(+), 13 deletions(-)

diff --git a/drivers/tty/serial/8250/8250.h b/drivers/tty/serial/8250/8250.h
index 696030cfcb09..c89cb881d9b0 100644
--- 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 3f56dbc9432b..82726cda6066 100644
--- a/drivers/tty/serial/8250/8250_core.c
+++ b/drivers/tty/serial/8250/8250_core.c
@@ -277,8 +277,7 @@ 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 3c36a06a20b0..c9d8c0de56e5 100644
--- a/drivers/tty/serial/8250/8250_port.c
+++ b/drivers/tty/serial/8250/8250_port.c
@@ -1514,11 +1514,9 @@ 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;
/*
@@ -1573,10 +1571,8 @@ 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);
}
@@ -2007,8 +2003,7 @@ 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);
@@ -2084,9 +2079,7 @@ 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;
--
2.35.1