[PATCH tty-next v5 4/6] serial: 8250: Provide flag for IER toggling for RS485
From: John Ogness <john.ogness@linutronix.de>
Date: 2025-01-07 21:27:07
Also in:
linux-serial, lkml
Subsystem:
8250/16?50 (and clone uarts) serial driver, the rest, tty layer and serial drivers · Maintainers:
Greg Kroah-Hartman, Linus Torvalds, Jiri Slaby
For RS485 mode, if SER_RS485_RX_DURING_TX is not available, the console ->write() callback needs to enable/disable Tx. It does this by calling the ->rs485_start_tx() and ->rs485_stop_tx() callbacks. However, some of these callbacks also disable/enable interrupts and makes power management calls. This causes 2 problems for console writing: 1. A console write can occur in contexts that are illegal for pm_runtime_*(). It is not even necessary for console writing to use pm_runtime_*() because a console already does this in serial8250_console_setup() and serial8250_console_exit(). 2. The console ->write() callback already handles disabling/enabling the interrupts by properly restoring the previous IER value. Add an argument @toggle_ier to the ->rs485_start_tx() and ->rs485_stop_tx() callbacks to specify if they may disable/enable receive interrupts while using pm_runtime_*(). Console writing will not allow the toggling. For all call sites other than console writing there is no functional change. Signed-off-by: John Ogness <john.ogness@linutronix.de> Reviewed-by: Petr Mladek <pmladek@suse.com> --- drivers/tty/serial/8250/8250.h | 4 ++-- drivers/tty/serial/8250/8250_bcm2835aux.c | 4 ++-- drivers/tty/serial/8250/8250_omap.c | 2 +- drivers/tty/serial/8250/8250_port.c | 26 +++++++++++++---------- include/linux/serial_8250.h | 4 ++-- 5 files changed, 22 insertions(+), 18 deletions(-)
diff --git a/drivers/tty/serial/8250/8250.h b/drivers/tty/serial/8250/8250.h
index e5310c65cf52..11e05aa014e5 100644
--- a/drivers/tty/serial/8250/8250.h
+++ b/drivers/tty/serial/8250/8250.h@@ -231,8 +231,8 @@ void serial8250_rpm_put_tx(struct uart_8250_port *p); int serial8250_em485_config(struct uart_port *port, struct ktermios *termios, struct serial_rs485 *rs485); -void serial8250_em485_start_tx(struct uart_8250_port *p); -void serial8250_em485_stop_tx(struct uart_8250_port *p); +void serial8250_em485_start_tx(struct uart_8250_port *p, bool toggle_ier); +void serial8250_em485_stop_tx(struct uart_8250_port *p, bool toggle_ier); void serial8250_em485_destroy(struct uart_8250_port *p); extern struct serial_rs485 serial8250_em485_supported;
diff --git a/drivers/tty/serial/8250/8250_bcm2835aux.c b/drivers/tty/serial/8250/8250_bcm2835aux.c
index fdb53b54e99e..0609582a62f7 100644
--- a/drivers/tty/serial/8250/8250_bcm2835aux.c
+++ b/drivers/tty/serial/8250/8250_bcm2835aux.c@@ -46,7 +46,7 @@ struct bcm2835aux_data { u32 cntl; }; -static void bcm2835aux_rs485_start_tx(struct uart_8250_port *up) +static void bcm2835aux_rs485_start_tx(struct uart_8250_port *up, bool toggle_ier) { if (!(up->port.rs485.flags & SER_RS485_RX_DURING_TX)) { struct bcm2835aux_data *data = dev_get_drvdata(up->port.dev);
@@ -65,7 +65,7 @@ static void bcm2835aux_rs485_start_tx(struct uart_8250_port *up) serial8250_out_MCR(up, UART_MCR_RTS); } -static void bcm2835aux_rs485_stop_tx(struct uart_8250_port *up) +static void bcm2835aux_rs485_stop_tx(struct uart_8250_port *up, bool toggle_ier) { if (up->port.rs485.flags & SER_RS485_RTS_AFTER_SEND) serial8250_out_MCR(up, 0);
diff --git a/drivers/tty/serial/8250/8250_omap.c b/drivers/tty/serial/8250/8250_omap.c
index 42b4aa56b902..c2b75e3f106d 100644
--- a/drivers/tty/serial/8250/8250_omap.c
+++ b/drivers/tty/serial/8250/8250_omap.c@@ -365,7 +365,7 @@ static void omap8250_restore_regs(struct uart_8250_port *up) if (up->port.rs485.flags & SER_RS485_ENABLED && up->port.rs485_config == serial8250_em485_config) - serial8250_em485_stop_tx(up); + serial8250_em485_stop_tx(up, true); } /*
diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
index 15abd95fcf06..d7976a21cca9 100644
--- a/drivers/tty/serial/8250/8250_port.c
+++ b/drivers/tty/serial/8250/8250_port.c@@ -578,7 +578,7 @@ static int serial8250_em485_init(struct uart_8250_port *p) deassert_rts: if (p->em485->tx_stopped) - p->rs485_stop_tx(p); + p->rs485_stop_tx(p, true); return 0; }
@@ -1398,10 +1398,11 @@ static void serial8250_stop_rx(struct uart_port *port) /** * serial8250_em485_stop_tx() - generic ->rs485_stop_tx() callback * @p: uart 8250 port + * @toggle_ier: true to allow enabling receive interrupts * * Generic callback usable by 8250 uart drivers to stop rs485 transmission. */ -void serial8250_em485_stop_tx(struct uart_8250_port *p) +void serial8250_em485_stop_tx(struct uart_8250_port *p, bool toggle_ier) { unsigned char mcr = serial8250_in_MCR(p);
@@ -1422,8 +1423,10 @@ void serial8250_em485_stop_tx(struct uart_8250_port *p) if (!(p->port.rs485.flags & SER_RS485_RX_DURING_TX)) { serial8250_clear_and_reinit_fifos(p); - p->ier |= UART_IER_RLSI | UART_IER_RDI; - serial_port_out(&p->port, UART_IER, p->ier); + if (toggle_ier) { + p->ier |= UART_IER_RLSI | UART_IER_RDI; + serial_port_out(&p->port, UART_IER, p->ier); + } } } EXPORT_SYMBOL_GPL(serial8250_em485_stop_tx);
@@ -1438,7 +1441,7 @@ static enum hrtimer_restart serial8250_em485_handle_stop_tx(struct hrtimer *t) serial8250_rpm_get(p); uart_port_lock_irqsave(&p->port, &flags); if (em485->active_timer == &em485->stop_tx_timer) { - p->rs485_stop_tx(p); + p->rs485_stop_tx(p, true); em485->active_timer = NULL; em485->tx_stopped = true; }
@@ -1470,7 +1473,7 @@ static void __stop_tx_rs485(struct uart_8250_port *p, u64 stop_delay) em485->active_timer = &em485->stop_tx_timer; hrtimer_start(&em485->stop_tx_timer, ns_to_ktime(stop_delay), HRTIMER_MODE_REL); } else { - p->rs485_stop_tx(p); + p->rs485_stop_tx(p, true); em485->active_timer = NULL; em485->tx_stopped = true; }
@@ -1559,6 +1562,7 @@ static inline void __start_tx(struct uart_port *port) /** * serial8250_em485_start_tx() - generic ->rs485_start_tx() callback * @up: uart 8250 port + * @toggle_ier: true to allow disabling receive interrupts * * 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.
@@ -1566,11 +1570,11 @@ static inline void __start_tx(struct uart_port *port) * 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.) */ -void serial8250_em485_start_tx(struct uart_8250_port *up) +void serial8250_em485_start_tx(struct uart_8250_port *up, bool toggle_ier) { unsigned char mcr = serial8250_in_MCR(up); - if (!(up->port.rs485.flags & SER_RS485_RX_DURING_TX)) + if (!(up->port.rs485.flags & SER_RS485_RX_DURING_TX) && toggle_ier) serial8250_stop_rx(&up->port); if (up->port.rs485.flags & SER_RS485_RTS_ON_SEND)
@@ -1604,7 +1608,7 @@ static bool start_tx_rs485(struct uart_port *port) if (em485->tx_stopped) { em485->tx_stopped = false; - up->rs485_start_tx(up); + up->rs485_start_tx(up, true); if (up->port.rs485.delay_rts_before_send > 0) { em485->active_timer = &em485->start_tx_timer;
@@ -3424,7 +3428,7 @@ void serial8250_console_write(struct uart_8250_port *up, const char *s, if (em485) { if (em485->tx_stopped) - up->rs485_start_tx(up); + up->rs485_start_tx(up, false); mdelay(port->rs485.delay_rts_before_send); }
@@ -3462,7 +3466,7 @@ void serial8250_console_write(struct uart_8250_port *up, const char *s, if (em485) { mdelay(port->rs485.delay_rts_after_send); if (em485->tx_stopped) - up->rs485_stop_tx(up); + up->rs485_stop_tx(up, false); } serial_port_out(port, UART_IER, ier);
diff --git a/include/linux/serial_8250.h b/include/linux/serial_8250.h
index e0717c8393d7..144de7a7948d 100644
--- a/include/linux/serial_8250.h
+++ b/include/linux/serial_8250.h@@ -161,8 +161,8 @@ struct uart_8250_port { void (*dl_write)(struct uart_8250_port *up, u32 value); struct uart_8250_em485 *em485; - void (*rs485_start_tx)(struct uart_8250_port *); - void (*rs485_stop_tx)(struct uart_8250_port *); + void (*rs485_start_tx)(struct uart_8250_port *up, bool toggle_ier); + void (*rs485_stop_tx)(struct uart_8250_port *up, bool toggle_ier); /* Serial port overrun backoff */ struct delayed_work overrun_backoff;
--
2.39.5