From 501e87c5f421654e1bb6fd4a25de46420549cae8 Mon Sep 17 00:00:00 2001 From: Phil Elwell Date: Mon, 24 Apr 2023 11:48:31 +0100 Subject: [PATCH] serial: 8250: Add NOMSI bug for bcm2835aux The BCM2835 mini-UART has no modem status interrupt, causing all transmission to stop, never to use, if a speed change ever happens while the CTS signal is high. Add a simple polling mechanism in order to allow recovery in that situation. Signed-off-by: Phil Elwell --- drivers/tty/serial/8250/8250.h | 1 + drivers/tty/serial/8250/8250_bcm2835aux.c | 1 + drivers/tty/serial/8250/8250_core.c | 15 +++++++++++++++ drivers/tty/serial/8250/8250_port.c | 9 +++++++++ 4 files changed, 26 insertions(+) --- a/drivers/tty/serial/8250/8250.h +++ b/drivers/tty/serial/8250/8250.h @@ -92,6 +92,7 @@ struct serial8250_config { #define UART_BUG_NOMSR BIT(2) /* UART has buggy MSR status bits (Au1x00) */ #define UART_BUG_THRE BIT(3) /* UART has buggy THRE reassertion */ #define UART_BUG_TXRACE BIT(5) /* UART Tx fails to set remote DR */ +#define UART_BUG_NOMSI BIT(6) /* UART has no modem status interrupt */ #ifdef CONFIG_SERIAL_8250_SHARE_IRQ --- a/drivers/tty/serial/8250/8250_bcm2835aux.c +++ b/drivers/tty/serial/8250/8250_bcm2835aux.c @@ -109,6 +109,7 @@ static int bcm2835aux_serial_probe(struc UPF_SKIP_TEST | UPF_IOREMAP; up.port.rs485_config = serial8250_em485_config; up.port.rs485_supported = serial8250_em485_supported; + up.bugs |= UART_BUG_NOMSI; up.rs485_start_tx = bcm2835aux_rs485_start_tx; up.rs485_stop_tx = bcm2835aux_rs485_stop_tx; --- a/drivers/tty/serial/8250/8250_core.c +++ b/drivers/tty/serial/8250/8250_core.c @@ -252,6 +252,18 @@ static void serial8250_timeout(struct ti mod_timer(&up->timer, jiffies + uart_poll_timeout(&up->port)); } +static void serial8250_cts_poll_timeout(struct timer_list *t) +{ + struct uart_8250_port *up = from_timer(up, t, timer); + unsigned long flags; + + spin_lock_irqsave(&up->port.lock, flags); + serial8250_modem_status(up); + spin_unlock_irqrestore(&up->port.lock, flags); + if (up->port.hw_stopped) + mod_timer(&up->timer, jiffies + 1); +} + static void serial8250_backup_timeout(struct timer_list *t) { struct uart_8250_port *up = from_timer(up, t, timer); @@ -314,6 +326,9 @@ static void univ8250_setup_timer(struct uart_poll_timeout(port) + HZ / 5); } + if (up->bugs & UART_BUG_NOMSI) + up->timer.function = serial8250_cts_poll_timeout; + /* * If the "interrupt" for this port doesn't correspond with any * hardware interrupt, we use a timer-based system. The original --- a/drivers/tty/serial/8250/8250_port.c +++ b/drivers/tty/serial/8250/8250_port.c @@ -1553,6 +1553,9 @@ static void serial8250_stop_tx(struct ua serial_icr_write(up, UART_ACR, up->acr); } serial8250_rpm_put(up); + + if (port->hw_stopped && (up->bugs & UART_BUG_NOMSI)) + mod_timer(&up->timer, jiffies + 1); } static inline void __start_tx(struct uart_port *port) @@ -1663,6 +1666,9 @@ static void serial8250_start_tx(struct u struct uart_8250_port *up = up_to_u8250p(port); struct uart_8250_em485 *em485 = up->em485; + if (up->bugs & UART_BUG_NOMSI) + del_timer(&up->timer); + if (!port->x_char && uart_circ_empty(&port->state->xmit)) return; @@ -1883,6 +1889,9 @@ unsigned int serial8250_modem_status(str uart_handle_cts_change(port, status & UART_MSR_CTS); wake_up_interruptible(&port->state->port.delta_msr_wait); + } else if (up->bugs & UART_BUG_NOMSI && port->hw_stopped && + status & UART_MSR_CTS) { + uart_handle_cts_change(port, status & UART_MSR_CTS); } return status;