[tty-next,v5,5/6] serial: 8250: Switch to nbcon console

Message ID	20250107212702.169493-6-john.ogness@linutronix.de
State	New
Headers	show Received: from galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id E9DAC1F76C4; Tue, 7 Jan 2025 21:27:08 +0000 (UTC) From: John Ogness <john.ogness@linutronix.de> To: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Cc: Jiri Slaby <jirislaby@kernel.org>, Petr Mladek <pmladek@suse.com>, Sergey Senozhatsky <senozhatsky@chromium.org>, Steven Rostedt <rostedt@goodmis.org>, Thomas Gleixner <tglx@linutronix.de>, Esben Haabendal <esben@geanix.com>, linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org, Andy Shevchenko <andriy.shevchenko@linux.intel.com>, Arnd Bergmann <arnd@arndb.de>, Tony Lindgren <tony@atomide.com>, Niklas Schnelle <schnelle@linux.ibm.com>, Serge Semin <fancer.lancer@gmail.com> Subject: [PATCH tty-next v5 5/6] serial: 8250: Switch to nbcon console Date: Tue, 7 Jan 2025 22:33:01 +0106 Message-Id: <20250107212702.169493-6-john.ogness@linutronix.de> In-Reply-To: <20250107212702.169493-1-john.ogness@linutronix.de> References: <20250107212702.169493-1-john.ogness@linutronix.de> Precedence: bulk MIME-Version: 1.0 Content-Transfer-Encoding: 8bit
Series	convert 8250 to nbcon \| expand [tty-next,v5,0/6] convert 8250 to nbcon [tty-next,v5,1/6] serial: 8250: Adjust the timeout for FIFO mode [tty-next,v5,2/6] serial: 8250: Use frame time to determine timeout [tty-next,v5,3/6] serial: 8250: Use high-level writing function for FIFO [tty-next,v5,4/6] serial: 8250: Provide flag for IER toggling for RS485 [tty-next,v5,5/6] serial: 8250: Switch to nbcon console [tty-next,v5,6/6] serial: 8250: Revert "drop lockdep annotation from serial8250_clear_IER()"

diff --git a/drivers/tty/serial/8250/8250_core.c b/drivers/tty/serial/8250/8250_core.c index 2b70e82dffeb..3d5a2183ff13 100644 --- a/drivers/tty/serial/8250/8250_core.c +++ b/drivers/tty/serial/8250/8250_core.c @@ -388,12 +388,34 @@ void __init serial8250_register_ports(struct uart_driver *drv, struct device *de #ifdef CONFIG_SERIAL_8250_CONSOLE -static void univ8250_console_write(struct console *co, const char *s, - unsigned int count) +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(up, s, count); + serial8250_console_write(up, wctxt, true); +} + +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(up, wctxt, false); +} + +static void univ8250_console_device_lock(struct console *co, unsigned long *flags) +{ + struct uart_port *up = &serial8250_ports[co->index].port; + + __uart_port_lock_irqsave(up, flags); +} + +static void univ8250_console_device_unlock(struct console *co, unsigned long flags) +{ + struct uart_port *up = &serial8250_ports[co->index].port; + + __uart_port_unlock_irqrestore(up, flags); } static int univ8250_console_setup(struct console *co, char *options) @@ -494,12 +516,15 @@ static int univ8250_console_match(struct console *co, char *name, int idx, static struct console univ8250_console = { .name = "ttyS", - .write = univ8250_console_write, + .write_atomic = univ8250_console_write_atomic, + .write_thread = univ8250_console_write_thread, + .device_lock = univ8250_console_device_lock, + .device_unlock = univ8250_console_device_unlock, .device = uart_console_device, .setup = univ8250_console_setup, .exit = univ8250_console_exit, .match = univ8250_console_match, - .flags = CON_PRINTBUFFER | CON_ANYTIME, + .flags = CON_PRINTBUFFER | CON_ANYTIME | CON_NBCON, .index = -1, .data = &serial8250_reg, }; diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c index d7976a21cca9..08466cf10d73 100644 --- a/drivers/tty/serial/8250/8250_port.c +++ b/drivers/tty/serial/8250/8250_port.c @@ -711,7 +711,12 @@ 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 directly by the callback helper serial8250_console_write(), + * which may not require the port lock. Use serial8250_clear_IER() instead for + * all other cases. + */ +static void __serial8250_clear_IER(struct uart_8250_port *up) { if (up->capabilities & UART_CAP_UUE) serial_out(up, UART_IER, UART_IER_UUE); @@ -719,6 +724,11 @@ 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. @@ -1406,9 +1416,6 @@ void serial8250_em485_stop_tx(struct uart_8250_port *p, bool toggle_ier) { unsigned char mcr = serial8250_in_MCR(p); - /* Port locked to synchronize UART_IER access against the console. */ - lockdep_assert_held_once(&p->port.lock); - if (p->port.rs485.flags & SER_RS485_RTS_AFTER_SEND) mcr |= UART_MCR_RTS; else @@ -1424,6 +1431,16 @@ void serial8250_em485_stop_tx(struct uart_8250_port *p, bool toggle_ier) serial8250_clear_and_reinit_fifos(p); if (toggle_ier) { + /* + * Port locked to synchronize UART_IER access against + * the console. The lockdep_assert must be restricted + * to this condition because only here is it + * guaranteed that the port lock is held. The other + * hardware access in this function is synchronized + * by console ownership. + */ + lockdep_assert_held_once(&p->port.lock); + p->ier |= UART_IER_RLSI | UART_IER_RDI; serial_port_out(&p->port, UART_IER, p->ier); } @@ -3303,7 +3320,11 @@ EXPORT_SYMBOL_GPL(serial8250_set_defaults); static void serial8250_console_putchar(struct uart_port *port, unsigned char ch) { + struct uart_8250_port *up = up_to_u8250p(port); + serial_port_out(port, UART_TX, ch); + + up->console_line_ended = (ch == '\n'); } static void serial8250_console_wait_putchar(struct uart_port *port, unsigned char ch) @@ -3340,11 +3361,22 @@ static void serial8250_console_restore(struct uart_8250_port *up) serial8250_out_MCR(up, up->mcr | UART_MCR_DTR | UART_MCR_RTS); } -static void fifo_wait_for_lsr(struct uart_8250_port *up, unsigned int count) +static void fifo_wait_for_lsr(struct uart_8250_port *up, + struct nbcon_write_context *wctxt, + unsigned int count) { unsigned int i; for (i = 0; i < count; i++) { + /* + * Pass the ownership as quickly as possible to a higher + * priority context. Otherwise, its attempt to take over + * the ownership might timeout. The new owner will wait + * for UART_LSR_THRE before reusing the fifo. + */ + if (!nbcon_can_proceed(wctxt)) + return; + if (wait_for_lsr(up, UART_LSR_THRE)) return; } @@ -3357,20 +3389,29 @@ static void fifo_wait_for_lsr(struct uart_8250_port *up, unsigned int count) * to get empty. */ static void serial8250_console_fifo_write(struct uart_8250_port *up, - const char *s, unsigned int count) + struct nbcon_write_context *wctxt) { - const char *end = s + count; unsigned int fifosize = up->tx_loadsz; struct uart_port *port = &up->port; + const char *s = wctxt->outbuf; + const char *end = s + wctxt->len; unsigned int tx_count = 0; bool cr_sent = false; unsigned int i; while (s != end) { /* Allow timeout for each byte of a possibly full FIFO */ - fifo_wait_for_lsr(up, fifosize); + fifo_wait_for_lsr(up, wctxt, fifosize); + /* + * Fill the FIFO. If a handover or takeover occurs, writing + * must be aborted since wctxt->outbuf and wctxt->len are no + * longer valid. + */ for (i = 0; i < fifosize && s != end; ++i) { + if (!nbcon_enter_unsafe(wctxt)) + return; + if (*s == '\n' && !cr_sent) { serial8250_console_putchar(port, '\r'); cr_sent = true; @@ -3378,6 +3419,8 @@ static void serial8250_console_fifo_write(struct uart_8250_port *up, serial8250_console_putchar(port, *s++); cr_sent = false; } + + nbcon_exit_unsafe(wctxt); } tx_count = i; } @@ -3386,39 +3429,57 @@ static void serial8250_console_fifo_write(struct uart_8250_port *up, * Allow timeout for each byte written since the caller will only wait * for UART_LSR_BOTH_EMPTY using the timeout of a single character */ - fifo_wait_for_lsr(up, tx_count); + fifo_wait_for_lsr(up, wctxt, tx_count); +} + +static void serial8250_console_byte_write(struct uart_8250_port *up, + struct nbcon_write_context *wctxt) +{ + struct uart_port *port = &up->port; + const char *s = wctxt->outbuf; + const char *end = s + wctxt->len; + + /* + * Write out the message. If a handover or takeover occurs, writing + * must be aborted since wctxt->outbuf and wctxt->len are no longer + * valid. + */ + while (s != end) { + if (!nbcon_enter_unsafe(wctxt)) + return; + + uart_console_write(port, s++, 1, serial8250_console_wait_putchar); + + nbcon_exit_unsafe(wctxt); + } } /* - * Print a string to the serial port trying not to disturb - * any possible real use of the port... - * - * The console_lock must be held when we get here. + * Print a string to the serial port trying not to disturb + * any possible real use of the port... * - * Doing runtime PM is really a bad idea for the kernel console. - * Thus, we assume the function is called when device is powered up. + * Doing runtime PM is really a bad idea for the kernel console. + * Thus, assume it is called when device is powered up. */ -void serial8250_console_write(struct uart_8250_port *up, const char *s, - unsigned int count) +void serial8250_console_write(struct uart_8250_port *up, + struct nbcon_write_context *wctxt, + bool is_atomic) { struct uart_8250_em485 *em485 = up->em485; struct uart_port *port = &up->port; - unsigned long flags; - unsigned int ier, use_fifo; - int locked = 1; - - touch_nmi_watchdog(); + unsigned int ier; + bool use_fifo; - if (oops_in_progress) - locked = uart_port_trylock_irqsave(port, &flags); - else - uart_port_lock_irqsave(port, &flags); + if (!nbcon_enter_unsafe(wctxt)) + return; /* - * First save the IER then disable the interrupts + * First, save the IER, then disable the interrupts. The special + * variant to clear the IER is used because console printing may + * occur without holding the port lock. */ 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))) { @@ -3432,6 +3493,18 @@ void serial8250_console_write(struct uart_8250_port *up, const char *s, mdelay(port->rs485.delay_rts_before_send); } + /* If ownership was lost, no writing is allowed */ + if (!nbcon_can_proceed(wctxt)) + goto skip_write; + + /* + * If console printer did not fully output the previous line, it must + * have been handed or taken over. Insert a newline in order to + * maintain clean output. + */ + if (!up->console_line_ended) + uart_console_write(port, "\n", 1, serial8250_console_wait_putchar); + use_fifo = (up->capabilities & UART_CAP_FIFO) && /* * BCM283x requires to check the fifo @@ -3452,10 +3525,23 @@ void serial8250_console_write(struct uart_8250_port *up, const char *s, */ !(up->port.flags & UPF_CONS_FLOW); + nbcon_exit_unsafe(wctxt); + if (likely(use_fifo)) - serial8250_console_fifo_write(up, s, count); + serial8250_console_fifo_write(up, wctxt); else - uart_console_write(port, s, count, serial8250_console_wait_putchar); + serial8250_console_byte_write(up, wctxt); +skip_write: + /* + * If ownership was lost, this context must reacquire ownership and + * re-enter the unsafe section in order to perform final actions + * (such as re-enabling interrupts). + */ + if (!nbcon_can_proceed(wctxt)) { + do { + nbcon_reacquire_nobuf(wctxt); + } while (!nbcon_enter_unsafe(wctxt)); + } /* * Finally, wait for transmitter to become empty @@ -3478,11 +3564,18 @@ void serial8250_console_write(struct uart_8250_port *up, const char *s, * 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); + if (up->msr_saved_flags) { + /* + * For atomic, it must be deferred to irq_work because this + * may be a context that does not permit waking up tasks. + */ + if (is_atomic) + irq_work_queue(&up->modem_status_work); + else + serial8250_modem_status(up); + } - if (locked) - uart_port_unlock_irqrestore(port, flags); + nbcon_exit_unsafe(wctxt); } static unsigned int probe_baud(struct uart_port *port) @@ -3500,8 +3593,24 @@ static unsigned int probe_baud(struct uart_port *port) return (port->uartclk / 16) / quot; } +/* + * irq_work handler to perform modem control. Only triggered via + * ->write_atomic() callback because it may be in a scheduler or + * NMI context, unable to wake tasks. + */ +static void modem_status_handler(struct irq_work *iwp) +{ + struct uart_8250_port *up = container_of(iwp, struct uart_8250_port, modem_status_work); + struct uart_port *port = &up->port; + + uart_port_lock(port); + serial8250_modem_status(up); + uart_port_unlock(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'; @@ -3511,6 +3620,9 @@ int serial8250_console_setup(struct uart_port *port, char *options, bool probe) if (!port->iobase && !port->membase) return -ENODEV; + up->console_line_ended = true; + init_irq_work(&up->modem_status_work, modem_status_handler); + 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 144de7a7948d..57875c37023a 100644 --- a/include/linux/serial_8250.h +++ b/include/linux/serial_8250.h @@ -150,8 +150,17 @@ struct uart_8250_port { #define LSR_SAVE_FLAGS UART_LSR_BRK_ERROR_BITS u16 lsr_saved_flags; u16 lsr_save_mask; + + /* + * Track when a console line has been fully written to the + * hardware, i.e. true when the most recent byte written to + * UART_TX by the console was '\n'. + */ + bool console_line_ended; + #define MSR_SAVE_FLAGS UART_MSR_ANY_DELTA unsigned char msr_saved_flags; + struct irq_work modem_status_work; struct uart_8250_dma *dma; const struct uart_8250_ops *ops; @@ -202,8 +211,8 @@ void serial8250_tx_chars(struct uart_8250_port *up); unsigned int serial8250_modem_status(struct uart_8250_port *up); 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(struct uart_8250_port *up, + struct nbcon_write_context *wctxt, bool in_atomic); int serial8250_console_setup(struct uart_port *port, char *options, bool probe); int serial8250_console_exit(struct uart_port *port);

[tty-next,v5,5/6] serial: 8250: Switch to nbcon console

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