[PATCH next v2 1/4] serial: 8250: Split out IER from rs485_start_tx()

John Ogness
2024-09-13T14:05:42Z

Move IER handling out of rs485_start_tx() callback and into a new
wrapper serial8250_rs485_start_tx(). Replace all callback call sites
with wrapper, except for the console write() callback, where it is
inappropriate to modify IER.

Signed-off-by: John Ogness <john.ogness@linutronix.de>
---
drivers/tty/serial/8250/8250.h | 2 ++
drivers/tty/serial/8250/8250_port.c | 27 +++++++++++++++++++++------
2 files changed, 23 insertions(+), 6 deletions(-)

diff --git a/drivers/tty/serial/8250/8250.h b/drivers/tty/serial/8250/8250.h
index e5310c65cf52..6e90223ba1d6 100644
--- a/drivers/tty/serial/8250/8250.h
+++ b/drivers/tty/serial/8250/8250.h
@@ -236,6 +236,8 @@ void serial8250_em485_stop_tx(struct uart_8250_port *p);
void serial8250_em485_destroy(struct uart_8250_port *p);
extern struct serial_rs485 serial8250_em485_supported;

+void serial8250_rs485_start_tx(struct uart_8250_port *up);
+
/* MCR <-> TIOCM conversion */
static inline int serial8250_TIOCM_to_MCR(int tiocm)
{
diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
index 2786918aea98..ba8d9cefc451 100644
--- a/drivers/tty/serial/8250/8250_port.c
+++ b/drivers/tty/serial/8250/8250_port.c
@@ -1370,7 +1370,6 @@ static void serial8250_stop_rx(struct uart_port *port)
serial8250_rpm_get(up);

up->ier &= ~(UART_IER_RLSI | UART_IER_RDI);
- up->port.read_status_mask &= ~UART_LSR_DR;
serial_port_out(port, UART_IER, up->ier);

serial8250_rpm_put(up);
@@ -1543,16 +1542,20 @@ static inline void __start_tx(struct uart_port *port)
*
* Generic callback usable by 8250 uart drivers to start rs485 transmission.
* Assumes that setting the RTS bit in the MCR register means RTS is high.
- * (Some chips use inverse semantics.) Further assumes that reception is
- * stoppable by disabling the UART_IER_RDI interrupt. (Some chips set the
- * UART_LSR_DR bit even when UART_IER_RDI is disabled, foiling this approach.)
+ * (Some chips use inverse semantics.)
+ * It does not disable RX interrupts. Use the wrapper function
+ * serial8250_rs485_start_tx() if that is also needed.
*/
void serial8250_em485_start_tx(struct uart_8250_port *up)
{
unsigned char mcr = serial8250_in_MCR(up);

+ /*
+ * Some chips set the UART_LSR_DR bit even when UART_IER_RDI is
+ * disabled, so explicitly mask it.
+ */
if (!(up->port.rs485.flags & SER_RS485_RX_DURING_TX))
- serial8250_stop_rx(&up->port);
+ up->port.read_status_mask &= ~UART_LSR_DR;

if (up->port.rs485.flags & SER_RS485_RTS_ON_SEND)
mcr |= UART_MCR_RTS;
@@ -1562,6 +1565,18 @@ void serial8250_em485_start_tx(struct uart_8250_port *up)
}
EXPORT_SYMBOL_GPL(serial8250_em485_start_tx);

+/**
+ * serial8250_rs485_start_tx() - stop rs485 reception, enable transmission
+ * @up: uart 8250 port
+ */
+void serial8250_rs485_start_tx(struct uart_8250_port *up)
+{
+ if (!(up->port.rs485.flags & SER_RS485_RX_DURING_TX))
+ serial8250_stop_rx(&up->port);
+
+ up->rs485_start_tx(up);
+}
+
/* Returns false, if start_tx_timer was setup to defer TX start */
static bool start_tx_rs485(struct uart_port *port)
{
@@ -1585,7 +1600,7 @@ static bool start_tx_rs485(struct uart_port *port)
if (em485->tx_stopped) {
em485->tx_stopped = false;

- up->rs485_start_tx(up);
+ serial8250_rs485_start_tx(up);

if (up->port.rs485.delay_rts_before_send > 0) {
em485->active_timer = &em485->start_tx_timer;
--
2.39.2