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Message-Id: <20240905134719.142554-2-john.ogness@linutronix.de>
Date: Thu, 5 Sep 2024 15:53:18 +0206
From: John Ogness <john.ogness@...utronix.de>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Jiri Slaby <jirislaby@...nel.org>,
Petr Mladek <pmladek@...e.com>,
Sergey Senozhatsky <senozhatsky@...omium.org>,
Steven Rostedt <rostedt@...dmis.org>,
Thomas Gleixner <tglx@...utronix.de>,
linux-serial@...r.kernel.org,
linux-kernel@...r.kernel.org,
Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
Tony Lindgren <tony@...mide.com>,
"Paul E. McKenney" <paulmck@...nel.org>,
Uwe Kleine-König <u.kleine-koenig@...gutronix.de>,
Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
Serge Semin <fancer.lancer@...il.com>,
Rengarajan S <rengarajan.s@...rochip.com>,
Wolfram Sang <wsa+renesas@...g-engineering.com>
Subject: [PATCH next v1 1/2] serial: 8250: Switch to nbcon console
Implement the necessary callbacks to switch the 8250 console driver
to perform as an nbcon console.
Add implementations for the nbcon console callbacks (write_atomic,
write_thread, device_lock, device_unlock) and add CON_NBCON to the
initial flags.
The legacy code is kept in order to easily switch back to legacy mode
by defining USE_SERIAL_8250_LEGACY_CONSOLE.
Signed-off-by: John Ogness <john.ogness@...utronix.de>
---
drivers/tty/serial/8250/8250_core.c | 42 +++++++-
drivers/tty/serial/8250/8250_port.c | 148 +++++++++++++++++++++++++++-
include/linux/serial_8250.h | 6 ++
3 files changed, 193 insertions(+), 3 deletions(-)
diff --git a/drivers/tty/serial/8250/8250_core.c b/drivers/tty/serial/8250/8250_core.c
index 29e4b83e0376..d7079931dd7e 100644
--- a/drivers/tty/serial/8250/8250_core.c
+++ b/drivers/tty/serial/8250/8250_core.c
@@ -388,6 +388,7 @@ void __init serial8250_register_ports(struct uart_driver *drv, struct device *de
#ifdef CONFIG_SERIAL_8250_CONSOLE
+#ifdef USE_SERIAL_8250_LEGACY_CONSOLE
static void univ8250_console_write(struct console *co, const char *s,
unsigned int count)
{
@@ -395,6 +396,37 @@ static void univ8250_console_write(struct console *co, const char *s,
serial8250_console_write(up, s, count);
}
+#else
+static void univ8250_console_write_atomic(struct console *co,
+ struct nbcon_write_context *wctxt)
+{
+ struct uart_8250_port *up = &serial8250_ports[co->index];
+
+ serial8250_console_write_atomic(up, wctxt);
+}
+
+static void univ8250_console_write_thread(struct console *co,
+ struct nbcon_write_context *wctxt)
+{
+ struct uart_8250_port *up = &serial8250_ports[co->index];
+
+ serial8250_console_write_thread(up, wctxt);
+}
+
+static void univ8250_console_device_lock(struct console *con, unsigned long *flags)
+{
+ struct uart_port *up = &serial8250_ports[con->index].port;
+
+ __uart_port_lock_irqsave(up, flags);
+}
+
+static void univ8250_console_device_unlock(struct console *con, unsigned long flags)
+{
+ struct uart_port *up = &serial8250_ports[con->index].port;
+
+ __uart_port_unlock_irqrestore(up, flags);
+}
+#endif /* USE_SERIAL_8250_LEGACY_CONSOLE */
static int univ8250_console_setup(struct console *co, char *options)
{
@@ -494,12 +526,20 @@ static int univ8250_console_match(struct console *co, char *name, int idx,
static struct console univ8250_console = {
.name = "ttyS",
+#ifdef USE_SERIAL_8250_LEGACY_CONSOLE
.write = univ8250_console_write,
+ .flags = CON_PRINTBUFFER | CON_ANYTIME,
+#else
+ .write_atomic = univ8250_console_write_atomic,
+ .write_thread = univ8250_console_write_thread,
+ .device_lock = univ8250_console_device_lock,
+ .device_unlock = univ8250_console_device_unlock,
+ .flags = CON_PRINTBUFFER | CON_ANYTIME | CON_NBCON,
+#endif
.device = uart_console_device,
.setup = univ8250_console_setup,
.exit = univ8250_console_exit,
.match = univ8250_console_match,
- .flags = CON_PRINTBUFFER | CON_ANYTIME,
.index = -1,
.data = &serial8250_reg,
};
diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
index 3509af7dc52b..ce841c62900d 100644
--- a/drivers/tty/serial/8250/8250_port.c
+++ b/drivers/tty/serial/8250/8250_port.c
@@ -546,6 +546,13 @@ static int serial8250_em485_init(struct uart_8250_port *p)
if (!p->em485)
return -ENOMEM;
+#ifndef USE_SERIAL_8250_LEGACY_CONSOLE
+ if (uart_console(&p->port)) {
+ dev_warn(p->port.dev, "no atomic printing for rs485 consoles\n");
+ p->port.cons->write_atomic = NULL;
+ }
+#endif
+
hrtimer_init(&p->em485->stop_tx_timer, CLOCK_MONOTONIC,
HRTIMER_MODE_REL);
hrtimer_init(&p->em485->start_tx_timer, CLOCK_MONOTONIC,
@@ -691,7 +698,11 @@ static void serial8250_set_sleep(struct uart_8250_port *p, int sleep)
serial8250_rpm_put(p);
}
-static void serial8250_clear_IER(struct uart_8250_port *up)
+/*
+ * Only to be used by write_atomic() and the legacy write(), which do not
+ * require port lock.
+ */
+static void __serial8250_clear_IER(struct uart_8250_port *up)
{
if (up->capabilities & UART_CAP_UUE)
serial_out(up, UART_IER, UART_IER_UUE);
@@ -699,6 +710,11 @@ static void serial8250_clear_IER(struct uart_8250_port *up)
serial_out(up, UART_IER, 0);
}
+static inline void serial8250_clear_IER(struct uart_8250_port *up)
+{
+ __serial8250_clear_IER(up);
+}
+
#ifdef CONFIG_SERIAL_8250_RSA
/*
* Attempts to turn on the RSA FIFO. Returns zero on failure.
@@ -3269,6 +3285,11 @@ static void serial8250_console_putchar(struct uart_port *port, unsigned char ch)
wait_for_xmitr(up, UART_LSR_THRE);
serial_port_out(port, UART_TX, ch);
+
+ if (ch == '\n')
+ up->console_newline_needed = false;
+ else
+ up->console_newline_needed = true;
}
/*
@@ -3297,6 +3318,7 @@ static void serial8250_console_restore(struct uart_8250_port *up)
serial8250_out_MCR(up, up->mcr | UART_MCR_DTR | UART_MCR_RTS);
}
+#ifdef USE_SERIAL_8250_LEGACY_CONSOLE
/*
* Print a string to the serial port using the device FIFO
*
@@ -3355,7 +3377,7 @@ void serial8250_console_write(struct uart_8250_port *up, const char *s,
* First save the IER then disable the interrupts
*/
ier = serial_port_in(port, UART_IER);
- serial8250_clear_IER(up);
+ __serial8250_clear_IER(up);
/* check scratch reg to see if port powered off during system sleep */
if (up->canary && (up->canary != serial_port_in(port, UART_SCR))) {
@@ -3421,6 +3443,125 @@ void serial8250_console_write(struct uart_8250_port *up, const char *s,
if (locked)
uart_port_unlock_irqrestore(port, flags);
}
+#else
+void serial8250_console_write_thread(struct uart_8250_port *up,
+ struct nbcon_write_context *wctxt)
+{
+ struct uart_8250_em485 *em485 = up->em485;
+ struct uart_port *port = &up->port;
+ unsigned int ier;
+
+ touch_nmi_watchdog();
+
+ if (!nbcon_enter_unsafe(wctxt))
+ return;
+
+ /* First save IER then disable the interrupts. */
+ ier = serial_port_in(port, UART_IER);
+ serial8250_clear_IER(up);
+
+ /* Check scratch reg if port powered off during system sleep. */
+ if (up->canary && (up->canary != serial_port_in(port, UART_SCR))) {
+ serial8250_console_restore(up);
+ up->canary = 0;
+ }
+
+ if (em485) {
+ if (em485->tx_stopped)
+ up->rs485_start_tx(up);
+ mdelay(port->rs485.delay_rts_before_send);
+ }
+
+ if (nbcon_exit_unsafe(wctxt)) {
+ int len = READ_ONCE(wctxt->len);
+ int i;
+
+ /*
+ * Write out the message. Toggle unsafe for each byte in order
+ * to give another (higher priority) context the opportunity
+ * for a friendly takeover. If such a takeover occurs, this
+ * must abort writing since wctxt->outbuf and wctxt->len are
+ * no longer valid.
+ */
+ for (i = 0; i < len; i++) {
+ if (!nbcon_enter_unsafe(wctxt))
+ break;
+
+ uart_console_write(port, wctxt->outbuf + i, 1, serial8250_console_putchar);
+
+ if (!nbcon_exit_unsafe(wctxt))
+ break;
+ }
+ }
+
+ /*
+ * If ownership was lost, this context must reacquire ownership in
+ * order to perform final actions (such as re-enabling interrupts).
+ */
+ while (!nbcon_enter_unsafe(wctxt))
+ nbcon_reacquire_nobuf(wctxt);
+
+ /* Finally, wait for transmitter to become empty and restore IER. */
+ wait_for_xmitr(up, UART_LSR_BOTH_EMPTY);
+ if (em485) {
+ mdelay(port->rs485.delay_rts_after_send);
+ if (em485->tx_stopped)
+ up->rs485_stop_tx(up);
+ }
+ serial_port_out(port, UART_IER, ier);
+
+ /*
+ * The receive handling will happen properly because the receive ready
+ * bit will still be set; it is not cleared on read. However, modem
+ * control will not, we must call it if we have saved something in the
+ * saved flags while processing with interrupts off.
+ */
+ if (up->msr_saved_flags)
+ serial8250_modem_status(up);
+
+ nbcon_exit_unsafe(wctxt);
+}
+
+void serial8250_console_write_atomic(struct uart_8250_port *up,
+ struct nbcon_write_context *wctxt)
+{
+ struct uart_port *port = &up->port;
+ unsigned int ier;
+
+ /* Atomic console not supported for rs485 mode. */
+ if (WARN_ON_ONCE(up->em485))
+ return;
+
+ touch_nmi_watchdog();
+
+ if (!nbcon_enter_unsafe(wctxt))
+ return;
+
+ /*
+ * First save IER then disable the interrupts. The special variant to
+ * clear IER is used because atomic printing may occur without holding
+ * the port lock.
+ */
+ ier = serial_port_in(port, UART_IER);
+ __serial8250_clear_IER(up);
+
+ /* Check scratch reg if port powered off during system sleep. */
+ if (up->canary && (up->canary != serial_port_in(port, UART_SCR))) {
+ serial8250_console_restore(up);
+ up->canary = 0;
+ }
+
+ if (up->console_newline_needed)
+ uart_console_write(port, "\n", 1, serial8250_console_putchar);
+ uart_console_write(port, wctxt->outbuf, wctxt->len, serial8250_console_putchar);
+
+ /* Finally, wait for transmitter to become empty and restore IER. */
+ wait_for_xmitr(up, UART_LSR_BOTH_EMPTY);
+ serial_port_out(port, UART_IER, ier);
+
+ nbcon_exit_unsafe(wctxt);
+}
+#endif /* USE_SERIAL_8250_LEGACY_CONSOLE */
static unsigned int probe_baud(struct uart_port *port)
{
@@ -3439,6 +3580,7 @@ static unsigned int probe_baud(struct uart_port *port)
int serial8250_console_setup(struct uart_port *port, char *options, bool probe)
{
+ struct uart_8250_port *up = up_to_u8250p(port);
int baud = 9600;
int bits = 8;
int parity = 'n';
@@ -3448,6 +3590,8 @@ int serial8250_console_setup(struct uart_port *port, char *options, bool probe)
if (!port->iobase && !port->membase)
return -ENODEV;
+ up->console_newline_needed = false;
+
if (options)
uart_parse_options(options, &baud, &parity, &bits, &flow);
else if (probe)
diff --git a/include/linux/serial_8250.h b/include/linux/serial_8250.h
index e0717c8393d7..a968e6941237 100644
--- a/include/linux/serial_8250.h
+++ b/include/linux/serial_8250.h
@@ -153,6 +153,8 @@ struct uart_8250_port {
#define MSR_SAVE_FLAGS UART_MSR_ANY_DELTA
unsigned char msr_saved_flags;
+ bool console_newline_needed;
+
struct uart_8250_dma *dma;
const struct uart_8250_ops *ops;
@@ -204,6 +206,10 @@ void serial8250_init_port(struct uart_8250_port *up);
void serial8250_set_defaults(struct uart_8250_port *up);
void serial8250_console_write(struct uart_8250_port *up, const char *s,
unsigned int count);
+void serial8250_console_write_atomic(struct uart_8250_port *up,
+ struct nbcon_write_context *wctxt);
+void serial8250_console_write_thread(struct uart_8250_port *up,
+ struct nbcon_write_context *wctxt);
int serial8250_console_setup(struct uart_port *port, char *options, bool probe);
int serial8250_console_exit(struct uart_port *port);
--
2.39.2
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