On Fri, Feb 14, 2020 at 01:43:35PM +0200, Andy Shevchenko wrote: > 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@xxxxxxxxxxx> > Signed-off-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx> > --- > Documentation/ABI/testing/sysfs-tty | 7 ++++ > drivers/tty/serial/serial_core.c | 60 +++++++++++++++++++++++++++-- > 2 files changed, 63 insertions(+), 4 deletions(-) > > diff --git a/Documentation/ABI/testing/sysfs-tty b/Documentation/ABI/testing/sysfs-tty > index 9eb3c2b6b040..e157130a6792 100644 > --- a/Documentation/ABI/testing/sysfs-tty > +++ b/Documentation/ABI/testing/sysfs-tty > @@ -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@xxxxxxxxxxxxxxx> > +Description: > + Allows user to detach or attach back the given device as > + kernel console. It shows and accepts a boolean variable. > diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c > index 7564bbd3061c..0415bb76efa0 100644 > --- a/drivers/tty/serial/serial_core.c > +++ b/drivers/tty/serial/serial_core.c > @@ -1919,7 +1919,7 @@ 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); > @@ -2749,6 +2749,56 @@ static ssize_t uart_get_attr_iomem_reg_shift(struct device *dev, > return snprintf(buf, PAGE_SIZE, "%d\n", tmp.iomem_reg_shift); > } > > +static ssize_t uart_get_attr_console(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 uart_set_attr_console(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(type, 0440, uart_get_attr_type, NULL); > static DEVICE_ATTR(line, 0440, uart_get_attr_line, NULL); > static DEVICE_ATTR(port, 0440, uart_get_attr_port, NULL); > @@ -2762,6 +2812,7 @@ static DEVICE_ATTR(custom_divisor, 0440, uart_get_attr_custom_divisor, NULL); > static DEVICE_ATTR(io_type, 0440, uart_get_attr_io_type, NULL); > static DEVICE_ATTR(iomem_base, 0440, uart_get_attr_iomem_base, NULL); > static DEVICE_ATTR(iomem_reg_shift, 0440, uart_get_attr_iomem_reg_shift, NULL); > +static DEVICE_ATTR(console, 0640, uart_get_attr_console, uart_set_attr_console); Again, DEVICE_ATTR_RW() in the future? thanks, greg k-h
