From nobody Sat Nov 30 03:44:17 2024 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 ABABD1DB95B; Fri, 13 Sep 2024 14:05:44 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=193.142.43.55 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1726236346; cv=none; b=I7AAyZ0RT6g+t7zD8myI+QYeV3ywS9Quq0GBpVftwFCO8ebss70JYYJyAHOPfzLESWD/N+3zNdAbUaRK8VXxz1k40X3Hd7fkm8vDgqABe7CA9N5xzOOMEmnFD5O+pHu4gIPRytPSr48Akr9XdbjCUDLe8Z9igtKaseexphYV75I= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1726236346; c=relaxed/simple; bh=Z4P8fplRtRJxbblPa1IezvMhKSCwBWjB0dsIGXU/7MY=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=NRUJ138/l3xb2Gj7tnHJFtT6p+2CoQ2df/gnMlSLCrVp0xEOwqXZSJ8KOuMCdJNmkx+FbCFktAX8Dv+OVWm4p/RCGGV6DAAdvx7pXC373MdTtQQrqdfPPNgK5moRBKwno87IL8poVGs/cnydagAdsuVeNvJD7G5zE2sQqXV4W94= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de; spf=pass smtp.mailfrom=linutronix.de; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=NeCuqiOV; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=nROeLSSr; arc=none smtp.client-ip=193.142.43.55 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linutronix.de Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="NeCuqiOV"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="nROeLSSr" From: John Ogness DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1726236342; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=W2qJgL7jg1r93GblbWHh8/o4/Jb12CtOJKsX7tOR3Bc=; b=NeCuqiOVND4UnhKFpsa1AgkLYbVfOSefh4BLd2tEJ6bOXBOkqoP1/j3J44eOJFq44/5UfM +zyvBSgyOZUb+KxGr/32trqsmbZvW3skCAkoaS07l48lfFMgYSqQNPgPZvEkaR6x2bhbFn vpksO1tksRWZKItTriqIbQMp2MKf2UQlgwU5aDQNYZoMLbiJ1wxY3tT8gNjcsYujtO8Ovy sTQkcnwxjaTTWuVjOCsUFevsmfFSZwDrj3oxz4Z0YVegqs0gj1pkAr+JBcMgHof0KQ6THx kfggRwItfDeEFJ8Gv6BmiZ6P2+GDnKgUokhpRnFYlTQ7RAV9elopeQ/PVIdVLQ== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1726236342; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=W2qJgL7jg1r93GblbWHh8/o4/Jb12CtOJKsX7tOR3Bc=; b=nROeLSSrUbe8oNFFUkX9fFEEURLg7Lfi8keZGvr/Gju+haqhbWDlK+z4wLpKAYC8wO8FAl cDyXia57DzkcUZDg== To: Greg Kroah-Hartman Cc: Jiri Slaby , Petr Mladek , Sergey Senozhatsky , Steven Rostedt , Thomas Gleixner , Esben Haabendal , linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org, Andy Shevchenko , Tony Lindgren , =?UTF-8?q?Ilpo=20J=C3=A4rvinen?= , =?UTF-8?q?Uwe=20Kleine-K=C3=B6nig?= , Arnd Bergmann , Florian Fainelli , Serge Semin , Wolfram Sang , Lino Sanfilippo Subject: [PATCH next v2 3/4] serial: 8250: Switch to nbcon console Date: Fri, 13 Sep 2024 16:11:37 +0206 Message-Id: <20240913140538.221708-4-john.ogness@linutronix.de> In-Reply-To: <20240913140538.221708-1-john.ogness@linutronix.de> References: <20240913140538.221708-1-john.ogness@linutronix.de> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" 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. All register access in the callbacks are within unsafe sections. The write_thread() callback allows safe handover/takeover per byte. The write_atomic() callback allows safe handover/takeover per printk record and adds a preceding newline if it took over mid-line. For the write_atomic() case, a new irq_work is used to defer modem control since it may be a context that does not allow waking up tasks. Signed-off-by: John Ogness Reviewed-by: Petr Mladek --- drivers/tty/serial/8250/8250_core.c | 35 +++++- drivers/tty/serial/8250/8250_port.c | 188 +++++++++++++++++----------- include/linux/serial_8250.h | 9 +- 3 files changed, 151 insertions(+), 81 deletions(-) diff --git a/drivers/tty/serial/8250/8250_core.c b/drivers/tty/serial/8250/= 8250_core.c index 5f9f06911795..2d690ff32a32 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_dri= ver *drv, struct device *de =20 #ifdef CONFIG_SERIAL_8250_CONSOLE =20 -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 =3D &serial8250_ports[co->index]; =20 - serial8250_console_write(up, s, count); + 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 =3D &serial8250_ports[co->index]; + + serial8250_console_write_thread(up, wctxt); +} + +static void univ8250_console_device_lock(struct console *con, unsigned lon= g *flags) +{ + struct uart_port *up =3D &serial8250_ports[con->index].port; + + __uart_port_lock_irqsave(up, flags); +} + +static void univ8250_console_device_unlock(struct console *con, unsigned l= ong flags) +{ + struct uart_port *up =3D &serial8250_ports[con->index].port; + + __uart_port_unlock_irqrestore(up, flags); } =20 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, =20 static struct console univ8250_console =3D { .name =3D "ttyS", - .write =3D univ8250_console_write, + .write_atomic =3D univ8250_console_write_atomic, + .write_thread =3D univ8250_console_write_thread, + .device_lock =3D univ8250_console_device_lock, + .device_unlock =3D univ8250_console_device_unlock, .device =3D uart_console_device, .setup =3D univ8250_console_setup, .exit =3D univ8250_console_exit, .match =3D univ8250_console_match, - .flags =3D CON_PRINTBUFFER | CON_ANYTIME, + .flags =3D CON_PRINTBUFFER | CON_ANYTIME | CON_NBCON, .index =3D -1, .data =3D &serial8250_reg, }; diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/= 8250_port.c index 7ee74ec944d2..d58a0fa95e3b 100644 --- a/drivers/tty/serial/8250/8250_port.c +++ b/drivers/tty/serial/8250/8250_port.c @@ -691,7 +691,12 @@ static void serial8250_set_sleep(struct uart_8250_port= *p, int sleep) serial8250_rpm_put(p); } =20 -static void serial8250_clear_IER(struct uart_8250_port *up) +/* + * Only to be used directly by the console write callbacks, 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); @@ -699,6 +704,11 @@ static void serial8250_clear_IER(struct uart_8250_port= *up) serial_out(up, UART_IER, 0); } =20 +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. @@ -1864,6 +1874,8 @@ unsigned int serial8250_modem_status(struct uart_8250= _port *up) struct uart_port *port =3D &up->port; unsigned int status =3D serial_in(up, UART_MSR); =20 + lockdep_assert_held_once(&port->lock); + status |=3D up->msr_saved_flags; up->msr_saved_flags =3D 0; if (status & UART_MSR_ANY_DELTA && up->ier & UART_IER_MSI && @@ -1884,6 +1896,21 @@ unsigned int serial8250_modem_status(struct uart_825= 0_port *up) } EXPORT_SYMBOL_GPL(serial8250_modem_status); =20 +/* + * 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 =3D container_of(iwp, struct uart_8250_port, mo= dem_status_work); + struct uart_port *port =3D &up->port; + + uart_port_lock(port); + serial8250_modem_status(up); + uart_port_unlock(port); +} + static bool handle_rx_dma(struct uart_8250_port *up, unsigned int iir) { switch (iir & 0x3f) { @@ -3296,6 +3323,11 @@ static void serial8250_console_putchar(struct uart_p= ort *port, unsigned char ch) =20 wait_for_xmitr(up, UART_LSR_THRE); serial_port_out(port, UART_TX, ch); + + if (ch =3D=3D '\n') + up->console_line_ended =3D true; + else + up->console_line_ended =3D false; } =20 /* @@ -3324,65 +3356,68 @@ static void serial8250_console_restore(struct uart_= 8250_port *up) serial8250_out_MCR(up, up->mcr | UART_MCR_DTR | UART_MCR_RTS); } =20 -/* - * Print a string to the serial port using the device FIFO - * - * It sends fifosize bytes and then waits for the fifo - * to get empty. - */ -static void serial8250_console_fifo_write(struct uart_8250_port *up, - const char *s, unsigned int count) +static void __serial8250_console_write_thread(struct uart_8250_port *up, + struct nbcon_write_context *wctxt) { - int i; - const char *end =3D s + count; - unsigned int fifosize =3D up->tx_loadsz; - bool cr_sent =3D false; - - while (s !=3D end) { - wait_for_lsr(up, UART_LSR_THRE); - - for (i =3D 0; i < fifosize && s !=3D end; ++i) { - if (*s =3D=3D '\n' && !cr_sent) { - serial_out(up, UART_TX, '\r'); - cr_sent =3D true; - } else { - serial_out(up, UART_TX, *s++); - cr_sent =3D false; - } + unsigned int len =3D READ_ONCE(wctxt->len); + struct uart_port *port =3D &up->port; + unsigned int i; + + if (nbcon_exit_unsafe(wctxt)) { + /* + * 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 =3D 0; i < len; i++) { + if (!nbcon_enter_unsafe(wctxt)) + break; + + uart_console_write(port, wctxt->outbuf + i, 1, serial8250_console_putch= ar); + + 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); } =20 -/* - * 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. - * - * Doing runtime PM is really a bad idea for the kernel console. - * Thus, we assume the function is called when device is powered up. - */ -void serial8250_console_write(struct uart_8250_port *up, const char *s, - unsigned int count) +static void __serial8250_console_write_atomic(struct uart_8250_port *up, + struct nbcon_write_context *wctxt) { - struct uart_8250_em485 *em485 =3D up->em485; struct uart_port *port =3D &up->port; - unsigned long flags; - unsigned int ier, use_fifo; - int locked =3D 1; =20 - touch_nmi_watchdog(); + if (!up->console_line_ended) + uart_console_write(port, "\n", 1, serial8250_console_putchar); + uart_console_write(port, wctxt->outbuf, wctxt->len, serial8250_console_pu= tchar); +} =20 - if (oops_in_progress) - locked =3D uart_port_trylock_irqsave(port, &flags); - else - uart_port_lock_irqsave(port, &flags); +static void serial8250_console_write(struct uart_8250_port *up, + struct nbcon_write_context *wctxt, + bool is_atomic) +{ + struct uart_8250_em485 *em485 =3D up->em485; + struct uart_port *port =3D &up->port; + unsigned int ier; + + if (!nbcon_enter_unsafe(wctxt)) + return; =20 /* - * First save the IER then disable the interrupts + * First save IER then disable the interrupts. The special variant + * to clear IER is used because console printing may occur without + * holding the port lock. */ ier =3D serial_port_in(port, UART_IER); - serial8250_clear_IER(up); + __serial8250_clear_IER(up); =20 /* check scratch reg to see if port powered off during system sleep */ if (up->canary && (up->canary !=3D serial_port_in(port, UART_SCR))) { @@ -3396,30 +3431,10 @@ void serial8250_console_write(struct uart_8250_port= *up, const char *s, mdelay(port->rs485.delay_rts_before_send); } =20 - use_fifo =3D (up->capabilities & UART_CAP_FIFO) && - /* - * BCM283x requires to check the fifo - * after each byte. - */ - !(up->capabilities & UART_CAP_MINI) && - /* - * tx_loadsz contains the transmit fifo size - */ - up->tx_loadsz > 1 && - (up->fcr & UART_FCR_ENABLE_FIFO) && - port->state && - test_bit(TTY_PORT_INITIALIZED, &port->state->port.iflags) && - /* - * After we put a data in the fifo, the controller will send - * it regardless of the CTS state. Therefore, only use fifo - * if we don't use control flow. - */ - !(up->port.flags & UPF_CONS_FLOW); - - if (likely(use_fifo)) - serial8250_console_fifo_write(up, s, count); + if (is_atomic) + __serial8250_console_write_atomic(up, wctxt); else - uart_console_write(port, s, count, serial8250_console_putchar); + __serial8250_console_write_thread(up, wctxt); =20 /* * Finally, wait for transmitter to become empty @@ -3442,11 +3457,32 @@ 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); + } =20 - if (locked) - uart_port_unlock_irqrestore(port, flags); + nbcon_exit_unsafe(wctxt); +} + +void serial8250_console_write_thread(struct uart_8250_port *up, + struct nbcon_write_context *wctxt) +{ + serial8250_console_write(up, wctxt, false); +} + +void serial8250_console_write_atomic(struct uart_8250_port *up, + struct nbcon_write_context *wctxt) +{ + touch_nmi_watchdog(); + + serial8250_console_write(up, wctxt, true); } =20 static unsigned int probe_baud(struct uart_port *port) @@ -3466,6 +3502,7 @@ static unsigned int probe_baud(struct uart_port *port) =20 int serial8250_console_setup(struct uart_port *port, char *options, bool p= robe) { + struct uart_8250_port *up =3D up_to_u8250p(port); int baud =3D 9600; int bits =3D 8; int parity =3D 'n'; @@ -3475,6 +3512,9 @@ int serial8250_console_setup(struct uart_port *port, = char *options, bool probe) if (!port->iobase && !port->membase) return -ENODEV; =20 + up->console_line_ended =3D true; + up->modem_status_work =3D IRQ_WORK_INIT(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 fd59ed2cca53..75c1f93fec73 100644 --- a/include/linux/serial_8250.h +++ b/include/linux/serial_8250.h @@ -152,6 +152,9 @@ struct uart_8250_port { u16 lsr_save_mask; #define MSR_SAVE_FLAGS UART_MSR_ANY_DELTA unsigned char msr_saved_flags; + struct irq_work modem_status_work; + + bool console_line_ended; /* line fully output */ =20 struct uart_8250_dma *dma; const struct uart_8250_ops *ops; @@ -202,8 +205,10 @@ 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_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 p= robe); int serial8250_console_exit(struct uart_port *port); =20 --=20 2.39.2