From: John Ogness Date: Wed, 13 Sep 2023 15:30:36 +0000 Subject: [PATCH 47/48] serial: 8250: Switch to nbcon console Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/6.10/older/patches-6.10.2-rt14.tar.xz 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 CONFIG_SERIAL_8250_LEGACY_CONSOLE. Signed-off-by: John Ogness Signed-off-by: Sebastian Andrzej Siewior --- drivers/tty/serial/8250/8250_core.c | 42 +++++++++ drivers/tty/serial/8250/8250_port.c | 154 +++++++++++++++++++++++++++++++++++- include/linux/serial_8250.h | 6 + 3 files changed, 199 insertions(+), 3 deletions(-) --- a/drivers/tty/serial/8250/8250_core.c +++ b/drivers/tty/serial/8250/8250_core.c @@ -589,6 +589,7 @@ serial8250_register_ports(struct uart_dr #ifdef CONFIG_SERIAL_8250_CONSOLE +#ifdef CONFIG_SERIAL_8250_LEGACY_CONSOLE static void univ8250_console_write(struct console *co, const char *s, unsigned int count) { @@ -596,6 +597,37 @@ static void univ8250_console_write(struc 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 /* CONFIG_SERIAL_8250_LEGACY_CONSOLE */ static int univ8250_console_setup(struct console *co, char *options) { @@ -695,12 +727,20 @@ static int univ8250_console_match(struct static struct console univ8250_console = { .name = "ttyS", +#ifdef CONFIG_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, }; --- 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 if (!p->em485) return -ENOMEM; +#ifndef CONFIG_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 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 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(s 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(s serial8250_out_MCR(up, up->mcr | UART_MCR_DTR | UART_MCR_RTS); } +#ifdef CONFIG_SERIAL_8250_LEGACY_CONSOLE /* * Print a string to the serial port using the device FIFO * @@ -3355,7 +3377,7 @@ void serial8250_console_write(struct uar * 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 +3443,131 @@ void serial8250_console_write(struct uar 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 + * context must reacquire ownership in order to perform final + * actions (such as re-enabling the interrupts). + * + * IMPORTANT: wctxt->outbuf and wctxt->len are no longer valid + * after a reacquire so writing the message must be + * aborted. + */ + for (i = 0; i < len; i++) { + if (!nbcon_enter_unsafe(wctxt)) { + nbcon_reacquire(wctxt); + break; + } + + uart_console_write(port, wctxt->outbuf + i, 1, serial8250_console_putchar); + + if (!nbcon_exit_unsafe(wctxt)) { + nbcon_reacquire(wctxt); + break; + } + } + } else { + nbcon_reacquire(wctxt); + } + + while (!nbcon_enter_unsafe(wctxt)) + nbcon_reacquire(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 /* CONFIG_SERIAL_8250_LEGACY_CONSOLE */ static unsigned int probe_baud(struct uart_port *port) { @@ -3439,6 +3586,7 @@ static unsigned int probe_baud(struct ua 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 +3596,8 @@ int serial8250_console_setup(struct uart 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) --- 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_82 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);