Commit a3cb39d2 authored by Andy Shevchenko's avatar Andy Shevchenko Committed by Greg Kroah-Hartman
Browse files

serial: core: Allow detach and attach serial device for console 

In the future we would like to disable power management on the serial devices
used as kernel consoles to avoid weird behaviour in some cases. However,
disabling PM may prevent system to go to deep sleep states, which in its turn
leads to the higher power consumption.

Tony Lindgren proposed a work around, i.e. allow user to detach such consoles
to make PM working again. In case user wants to see what's going on, it also
provides a mechanism to attach console back.

Link: https://lists.openwall.net/linux-kernel/2018/09/29/65


Suggested-by: default avatarTony Lindgren <tony@atomide.com>
Signed-off-by: default avatarAndy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20200217114016.49856-3-andriy.shevchenko@linux.intel.com


Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 5f3a4813

Documentation/ABI/testing/sysfs-tty

+7 −0
Original line number Diff line number Diff line
@@ -154,3 +154,10 @@ Description: 
		 device specification. For example, when user sets 7bytes on

		 16550A, which has 1/4/8/14 bytes trigger, the RX trigger is

		 automatically changed to 4 bytes.



What:		/sys/class/tty/ttyS0/console

Date:		February 2020

Contact:	Andy Shevchenko <andriy.shevchenko@linux.intel.com>

Description:

		 Allows user to detach or attach back the given device as

		 kernel console. It shows and accepts a boolean variable.

drivers/tty/serial/serial_core.c

+56 −4
Original line number Diff line number Diff line
@@ -1922,7 +1922,7 @@ static inline bool uart_console_enabled(struct uart_port *port) 
 */

static inline void uart_port_spin_lock_init(struct uart_port *port)

{

	if (uart_console_enabled(port))

	if (uart_console(port))

		return;



	spin_lock_init(&port->lock);
@@ -2751,6 +2751,56 @@ static ssize_t iomem_reg_shift_show(struct device *dev, 
	return snprintf(buf, PAGE_SIZE, "%d\n", tmp.iomem_reg_shift);

}



static ssize_t console_show(struct device *dev,

	struct device_attribute *attr, char *buf)

{

	struct tty_port *port = dev_get_drvdata(dev);

	struct uart_state *state = container_of(port, struct uart_state, port);

	struct uart_port *uport;

	bool console = false;



	mutex_lock(&port->mutex);

	uport = uart_port_check(state);

	if (uport)

		console = uart_console_enabled(uport);

	mutex_unlock(&port->mutex);



	return sprintf(buf, "%c\n", console ? 'Y' : 'N');

}



static ssize_t console_store(struct device *dev,

	struct device_attribute *attr, const char *buf, size_t count)

{

	struct tty_port *port = dev_get_drvdata(dev);

	struct uart_state *state = container_of(port, struct uart_state, port);

	struct uart_port *uport;

	bool oldconsole, newconsole;

	int ret;



	ret = kstrtobool(buf, &newconsole);

	if (ret)

		return ret;



	mutex_lock(&port->mutex);

	uport = uart_port_check(state);

	if (uport) {

		oldconsole = uart_console_enabled(uport);

		if (oldconsole && !newconsole) {

			ret = unregister_console(uport->cons);

		} else if (!oldconsole && newconsole) {

			if (uart_console(uport))

				register_console(uport->cons);

			else

				ret = -ENOENT;

		}

	} else {

		ret = -ENXIO;

	}

	mutex_unlock(&port->mutex);



	return ret < 0 ? ret : count;

}



static DEVICE_ATTR_RO(uartclk);

static DEVICE_ATTR_RO(type);

static DEVICE_ATTR_RO(line);
@@ -2764,6 +2814,7 @@ static DEVICE_ATTR_RO(custom_divisor); 
static DEVICE_ATTR_RO(io_type);

static DEVICE_ATTR_RO(iomem_base);

static DEVICE_ATTR_RO(iomem_reg_shift);

static DEVICE_ATTR_RW(console);



static struct attribute *tty_dev_attrs[] = {

	&dev_attr_uartclk.attr,
@@ -2779,7 +2830,8 @@ static struct attribute *tty_dev_attrs[] = { 
	&dev_attr_io_type.attr,

	&dev_attr_iomem_base.attr,

	&dev_attr_iomem_reg_shift.attr,

	NULL,

	&dev_attr_console.attr,

	NULL

};



static const struct attribute_group tty_dev_attr_group = {

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