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

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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: Tony Lindgren <tony@atomide.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20200217114016.49856-3-andriy.shevchenko@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Andy Shevchenko 2020-02-17 13:40:12 +02:00 committed by Greg Kroah-Hartman
parent 5f3a481324
commit a3cb39d258
2 changed files with 63 additions and 4 deletions
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7
Documentation/ABI/testing/sysfs-tty
View File

@ -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.

60
drivers/tty/serial/serial_core.c
View File

@ -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,
@ -2779,12 +2830,13 @@ 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 = {
.attrs = tty_dev_attrs,
};
};
/**
* uart_add_one_port - attach a driver-defined port structure