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From 501e87c5f421654e1bb6fd4a25de46420549cae8 Mon Sep 17 00:00:00 2001
From: Phil Elwell <phil@raspberrypi.com>
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 <phil@raspberrypi.com>
---
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;
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