From 058bc104f7ca5c83d81695ee96f03dbd93bae518 Mon Sep 17 00:00:00 2001 From: Lukas Wunner Date: Fri, 28 Feb 2020 14:31:06 +0100 Subject: serial: 8250: Generalize rs485 software emulation Commit e490c9144cfa ("tty: Add software emulated RS485 support for 8250") introduced support to use RTS as an rs485 Transmit Enable signal. So far the only drivers taking advantage of it are 8250_omap.c and 8250_of.c. We're about to make use of the feature in 8250_bcm2835aux.c as well. The bcm2835aux differs from omap chips by inverting the meaning of RTS in the MCR register. Moreover, omap achieves half-duplex mode by disabling the RX interrupt and clearing the RX FIFO when TX stops. The bcm2835aux requires disabling the receiver instead. Support these behavioral differences by generalizing the rs485 emulation: Introduce ->rs485_start_tx() and ->rs485_stop_tx() callbacks in struct uart_8250_port, provide generic implementations containing the existing code and use them as callbacks in 8250_omap.c and 8250_of.c. start_tx_rs485() is idempotent in that it recognizes whether RTS is already asserted. Achieve the same by introducing a tx_stopped flag in struct uart_8250_em485. This may even perform a little better on arches where memory access is faster than mmio access. Signed-off-by: Lukas Wunner Cc: Matwey V. Kornilov Link: https://lore.kernel.org/r/5ac0464ae4414708e723a1e0d52b0c1b2bd41b9b.1582895077.git.lukas@wunner.de Signed-off-by: Greg Kroah-Hartman --- include/linux/serial_8250.h | 3 +++ 1 file changed, 3 insertions(+) (limited to 'include/linux/serial_8250.h') diff --git a/include/linux/serial_8250.h b/include/linux/serial_8250.h index 6a8e8c48c882..0901c2aa366c 100644 --- a/include/linux/serial_8250.h +++ b/include/linux/serial_8250.h @@ -81,6 +81,7 @@ struct uart_8250_em485 { struct hrtimer stop_tx_timer; /* "rs485 stop tx" timer */ struct hrtimer *active_timer; /* pointer to active timer */ struct uart_8250_port *port; /* for hrtimer callbacks */ + unsigned int tx_stopped:1; /* tx is currently stopped */ }; /* @@ -132,6 +133,8 @@ struct uart_8250_port { void (*dl_write)(struct uart_8250_port *, int); struct uart_8250_em485 *em485; + void (*rs485_start_tx)(struct uart_8250_port *); + void (*rs485_stop_tx)(struct uart_8250_port *); /* Serial port overrun backoff */ struct delayed_work overrun_backoff; -- cgit v1.2.3 From bedb404e91bb2908d9921fc736a518a9d89525fc Mon Sep 17 00:00:00 2001 From: Andy Shevchenko Date: Mon, 17 Feb 2020 13:40:15 +0200 Subject: serial: 8250_port: Don't use power management for kernel console Doing any kind of power management for kernel console is really bad idea. First of all, it runs in poll and atomic mode. This fact attaches a limitation on the functions that might be called. For example, pm_runtime_get_sync() might sleep and thus can't be used. This call needs, for example, to bring the device to powered on state on the system, where the power on sequence may require on-atomic operations, such as Intel Cherrytrail with ACPI enumerated UARTs. That said, on ACPI enabled platforms it might even call firmware for a job. On the other hand pm_runtime_get() doesn't guarantee that device will become powered on fast enough. Besides that, imagine the case when console is about to print a kernel Oops and it's powered off. In such an emergency case calling the complex functions is not the best what we can do, taking into consideration that user wants to see at least something of the last kernel word before it passes away. Here we modify the 8250 console code to prevent runtime power management. Note, there is a behaviour change for OMAP boards. It will require to detach kernel console to become idle. Link: https://lists.openwall.net/linux-kernel/2018/09/29/65 Suggested-by: Russell King Signed-off-by: Andy Shevchenko Link: https://lore.kernel.org/r/20200217114016.49856-6-andriy.shevchenko@linux.intel.com Signed-off-by: Greg Kroah-Hartman --- drivers/tty/serial/8250/8250_core.c | 9 +++++++++ drivers/tty/serial/8250/8250_port.c | 24 ++++++++++++++++++++---- include/linux/serial_8250.h | 1 + 3 files changed, 30 insertions(+), 4 deletions(-) (limited to 'include/linux/serial_8250.h') diff --git a/drivers/tty/serial/8250/8250_core.c b/drivers/tty/serial/8250/8250_core.c index f6eb00406ddf..45d9117cab68 100644 --- a/drivers/tty/serial/8250/8250_core.c +++ b/drivers/tty/serial/8250/8250_core.c @@ -608,6 +608,14 @@ static int univ8250_console_setup(struct console *co, char *options) return retval; } +static int univ8250_console_exit(struct console *co) +{ + struct uart_port *port; + + port = &serial8250_ports[co->index].port; + return serial8250_console_exit(port); +} + /** * univ8250_console_match - non-standard console matching * @co: registering console @@ -666,6 +674,7 @@ static struct console univ8250_console = { .write = univ8250_console_write, .device = uart_console_device, .setup = univ8250_console_setup, + .exit = univ8250_console_exit, .match = univ8250_console_match, .flags = CON_PRINTBUFFER | CON_ANYTIME, .index = -1, diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c index 0879bb8855cf..c156a30c4dec 100644 --- a/drivers/tty/serial/8250/8250_port.c +++ b/drivers/tty/serial/8250/8250_port.c @@ -3200,6 +3200,9 @@ static void serial8250_console_restore(struct uart_8250_port *up) * 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) @@ -3212,8 +3215,6 @@ void serial8250_console_write(struct uart_8250_port *up, const char *s, touch_nmi_watchdog(); - serial8250_rpm_get(up); - if (oops_in_progress) locked = spin_trylock_irqsave(&port->lock, flags); else @@ -3268,7 +3269,6 @@ void serial8250_console_write(struct uart_8250_port *up, const char *s, if (locked) spin_unlock_irqrestore(&port->lock, flags); - serial8250_rpm_put(up); } static unsigned int probe_baud(struct uart_port *port) @@ -3292,6 +3292,7 @@ int serial8250_console_setup(struct uart_port *port, char *options, bool probe) int bits = 8; int parity = 'n'; int flow = 'n'; + int ret; if (!port->iobase && !port->membase) return -ENODEV; @@ -3301,7 +3302,22 @@ int serial8250_console_setup(struct uart_port *port, char *options, bool probe) else if (probe) baud = probe_baud(port); - return uart_set_options(port, port->cons, baud, parity, bits, flow); + ret = uart_set_options(port, port->cons, baud, parity, bits, flow); + if (ret) + return ret; + + if (port->dev) + pm_runtime_get_sync(port->dev); + + return 0; +} + +int serial8250_console_exit(struct uart_port *port) +{ + if (port->dev) + pm_runtime_put_sync(port->dev); + + return 0; } #endif /* CONFIG_SERIAL_8250_CONSOLE */ diff --git a/include/linux/serial_8250.h b/include/linux/serial_8250.h index 0901c2aa366c..6545f8cfc8fa 100644 --- a/include/linux/serial_8250.h +++ b/include/linux/serial_8250.h @@ -179,6 +179,7 @@ void serial8250_set_defaults(struct uart_8250_port *up); void serial8250_console_write(struct uart_8250_port *up, const char *s, unsigned int count); int serial8250_console_setup(struct uart_port *port, char *options, bool probe); +int serial8250_console_exit(struct uart_port *port); extern void serial8250_set_isa_configurator(void (*v) (int port, struct uart_port *up, -- cgit v1.2.3