[PATCH 1/2] serial: core: fix port-lock initialisation

[PATCH 1/2] serial: core: fix port-lock initialisation

[Johan Hovold]

Commit f743061a85f5 ("serial: core: Initialise spin lock before use in
uart_configure_port()") tried to work around a breakage introduced by
commit a3cb39d258ef ("serial: core: Allow detach and attach serial
device for console") by adding a second initialisation of the port lock
when registering the port.

As reported by the build robots [1], this doesn't really solve the
regression introduced by the console-detach changes and also adds a
second redundant initialisation of the lock for normal ports.

Start cleaning up this mess by removing the redundant initialisation and
making sure that the port lock is again initialised once-only for ports
that aren't already in use as a console.

[1] https://lore.kernel.org/r/20200802054852.GR23458@shao2-debian

Fixes: f743061a85f5 ("serial: core: Initialise spin lock before use in uart_configure_port()")
Fixes: a3cb39d258ef ("serial: core: Allow detach and attach serial device for console")
Cc: stable <stable@vger.kernel.org>     # 5.7
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Johan Hovold <johan@kernel.org>
---
 drivers/tty/serial/serial_core.c | 14 ++++++--------
 1 file changed, 6 insertions(+), 8 deletions(-)

diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
index f797c971cd82..53b79e1fcbc8 100644
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -2378,13 +2378,6 @@ uart_configure_port(struct uart_driver *drv, struct uart_state *state,
 		/* Power up port for set_mctrl() */
 		uart_change_pm(state, UART_PM_STATE_ON);
 
-		/*
-		 * If this driver supports console, and it hasn't been
-		 * successfully registered yet, initialise spin lock for it.
-		 */
-		if (port->cons && !(port->cons->flags & CON_ENABLED))
-			__uart_port_spin_lock_init(port);
-
 		/*
 		 * Ensure that the modem control lines are de-activated.
 		 * keep the DTR setting that is set in uart_set_options()
@@ -2900,7 +2893,12 @@ int uart_add_one_port(struct uart_driver *drv, struct uart_port *uport)
 		goto out;
 	}
 
-	uart_port_spin_lock_init(uport);
+	/*
+	 * If this port is in use as a console then the spinlock is already
+	 * initialised.
+	 */
+	if (!uart_console_enabled(uport))
+		__uart_port_spin_lock_init(uport);
 
 	if (uport->cons && uport->dev)
 		of_console_check(uport->dev->of_node, uport->cons->name, uport->line);
-- 
2.26.2

Re: [PATCH 1/2] serial: core: fix port-lock initialisation

[Johan Hovold]

On Wed, Sep 09, 2020 at 06:21:58PM +0300, Andy Shevchenko wrote:
> On Wed, Sep 09, 2020 at 04:31:00PM +0200, Johan Hovold wrote:
> > Commit f743061a85f5 ("serial: core: Initialise spin lock before use in
> > uart_configure_port()") tried to work around a breakage introduced by
> > commit a3cb39d258ef ("serial: core: Allow detach and attach serial
> > device for console") by adding a second initialisation of the port lock
> > when registering the port.
> > 
> > As reported by the build robots [1], this doesn't really solve the
> > regression introduced by the console-detach changes and also adds a
> > second redundant initialisation of the lock for normal ports.
> 
> I thought, though doubtfully, it was a regression made by
> 679193b7baf8 ("serial: 8250: Let serial core initialise spin lock")
> and then I completely forgot about [1].

Yes, that driver has had an explicit early initialisation of the lock
and it was indeed the removal of that which triggered the robot's
report. With the initialisation again done during console setup (patch
2/2), that should no longer be an issue (at least not for the console
port...).

> > Start cleaning up this mess by removing the redundant initialisation and
> > making sure that the port lock is again initialised once-only for ports
> > that aren't already in use as a console.
> 
> Thanks for looking into this!
> 
> I agree this is better place for lock initialization.
> Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>

Thanks for reviewing.

Johan

[PATCH 2/2] serial: core: fix console port-lock regression

[Johan Hovold]

Fix the port-lock initialisation regression introduced by commit
a3cb39d258ef ("serial: core: Allow detach and attach serial device for
console") by making sure that the lock is again initialised during
console setup.

The console may be registered before the serial controller has been
probed in which case the port lock needs to be initialised during
console setup by a call to uart_set_options(). The console-detach
changes introduced a regression in several drivers by effectively
removing that initialisation by not initialising the lock when the port
is used as a console (which is always the case during console setup).

Add back the early lock initialisation and instead use a new
console-reinit flag to handle the case where a console is being
re-attached through sysfs.

The question whether the console-detach interface should have been added
in the first place is left for another discussion.

Note that the console-enabled check in uart_set_options() is not
redundant because of kgdboc, which can end up reinitialising an already
enabled console (see commit 42b6a1baa3ec ("serial_core: Don't
re-initialize a previously initialized spinlock.")).

Fixes: a3cb39d258ef ("serial: core: Allow detach and attach serial device for console")
Cc: stable <stable@vger.kernel.org>     # 5.7
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Johan Hovold <johan@kernel.org>
---
 drivers/tty/serial/serial_core.c | 32 +++++++++++++++-----------------
 include/linux/serial_core.h      |  1 +
 2 files changed, 16 insertions(+), 17 deletions(-)

diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
index 53b79e1fcbc8..124524ecfe26 100644
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -1916,24 +1916,12 @@ static inline bool uart_console_enabled(struct uart_port *port)
 	return uart_console(port) && (port->cons->flags & CON_ENABLED);
 }
 
-static void __uart_port_spin_lock_init(struct uart_port *port)
+static void uart_port_spin_lock_init(struct uart_port *port)
 {
 	spin_lock_init(&port->lock);
 	lockdep_set_class(&port->lock, &port_lock_key);
 }
 
-/*
- * Ensure that the serial console lock is initialised early.
- * If this port is a console, then the spinlock is already initialised.
- */
-static inline void uart_port_spin_lock_init(struct uart_port *port)
-{
-	if (uart_console(port))
-		return;
-
-	__uart_port_spin_lock_init(port);
-}
-
 #if defined(CONFIG_SERIAL_CORE_CONSOLE) || defined(CONFIG_CONSOLE_POLL)
 /**
  *	uart_console_write - write a console message to a serial port
@@ -2086,7 +2074,15 @@ uart_set_options(struct uart_port *port, struct console *co,
 	struct ktermios termios;
 	static struct ktermios dummy;
 
-	uart_port_spin_lock_init(port);
+	/*
+	 * Ensure that the serial-console lock is initialised early.
+	 *
+	 * Note that the console-enabled check is needed because of kgdboc,
+	 * which can end up calling uart_set_options() for an already enabled
+	 * console via tty_find_polling_driver() and uart_poll_init().
+	 */
+	if (!uart_console_enabled(port) && !port->console_reinit)
+		uart_port_spin_lock_init(port);
 
 	memset(&termios, 0, sizeof(struct ktermios));
 
@@ -2794,10 +2790,12 @@ static ssize_t console_store(struct device *dev,
 		if (oldconsole && !newconsole) {
 			ret = unregister_console(uport->cons);
 		} else if (!oldconsole && newconsole) {
-			if (uart_console(uport))
+			if (uart_console(uport)) {
+				uport->console_reinit = 1;
 				register_console(uport->cons);
-			else
+			} else {
 				ret = -ENOENT;
+			}
 		}
 	} else {
 		ret = -ENXIO;
@@ -2898,7 +2896,7 @@ int uart_add_one_port(struct uart_driver *drv, struct uart_port *uport)
 	 * initialised.
 	 */
 	if (!uart_console_enabled(uport))
-		__uart_port_spin_lock_init(uport);
+		uart_port_spin_lock_init(uport);
 
 	if (uport->cons && uport->dev)
 		of_console_check(uport->dev->of_node, uport->cons->name, uport->line);
diff --git a/include/linux/serial_core.h b/include/linux/serial_core.h
index 01fc4d9c9c54..8a99279a579b 100644
--- a/include/linux/serial_core.h
+++ b/include/linux/serial_core.h
@@ -248,6 +248,7 @@ struct uart_port {
 
 	unsigned char		hub6;			/* this should be in the 8250 driver */
 	unsigned char		suspended;
+	unsigned char		console_reinit;
 	const char		*name;			/* port name */
 	struct attribute_group	*attr_group;		/* port specific attributes */
 	const struct attribute_group **tty_groups;	/* all attributes (serial core use only) */
-- 
2.26.2

Re: [PATCH 2/2] serial: core: fix console port-lock regression

[Johan Hovold]

On Wed, Sep 09, 2020 at 06:48:15PM +0300, Andy Shevchenko wrote:
> On Wed, Sep 09, 2020 at 04:31:01PM +0200, Johan Hovold wrote:
> > Fix the port-lock initialisation regression introduced by commit
> > a3cb39d258ef ("serial: core: Allow detach and attach serial device for
> > console") by making sure that the lock is again initialised during
> > console setup.
> > 
> > The console may be registered before the serial controller has been
> > probed in which case the port lock needs to be initialised during
> > console setup by a call to uart_set_options(). The console-detach
> > changes introduced a regression in several drivers by effectively
> > removing that initialisation by not initialising the lock when the port
> > is used as a console (which is always the case during console setup).
> > 
> > Add back the early lock initialisation and instead use a new
> > console-reinit flag to handle the case where a console is being
> > re-attached through sysfs.
> > 
> > The question whether the console-detach interface should have been added
> > in the first place is left for another discussion.
> 
> It was discussed in [1]. TL;DR: OMAP would like to keep runtime PM available
> for UART while at the same time we disable it for kernel consoles in
> bedb404e91bb.
> 
> [1]: https://lists.openwall.net/linux-kernel/2018/09/29/65

Yeah, I remember that. My fear is just that the new interface opens up a
can of worms as it removes the earlier assumption that the console would
essentially never be deregistered without really fixing all those
drivers, and core functions, written under that assumption. Just to
mention a few issues; we have drivers enabling clocks and other
resources during console setup which can now be done repeatedly, and
several drivers whose setup callbacks are marked __init and will oops
the minute you reattach the console. And what about power management
which was the reason for wanting this on OMAP in the first place; tty
core never calls shutdown() for a console port, not even when it's been
detached using the new interface.

I know, the console setup is all a mess, but this still seems a little
rushed to me. I'm even inclined to suggest a revert until the above and
similar issues have been addressed properly rather keeping a known buggy
interface.

> > Note that the console-enabled check in uart_set_options() is not
> > redundant because of kgdboc, which can end up reinitialising an already
> > enabled console (see commit 42b6a1baa3ec ("serial_core: Don't
> > re-initialize a previously initialized spinlock.")).
> 
> Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
> Thank you!
> 
> One question below, though.
> 
> > Fixes: a3cb39d258ef ("serial: core: Allow detach and attach serial device for console")
> > Cc: stable <stable@vger.kernel.org>     # 5.7
> > Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
> > Signed-off-by: Johan Hovold <johan@kernel.org>
> > ---
> >  drivers/tty/serial/serial_core.c | 32 +++++++++++++++-----------------
> >  include/linux/serial_core.h      |  1 +
> >  2 files changed, 16 insertions(+), 17 deletions(-)
> > 
> > diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
> > index 53b79e1fcbc8..124524ecfe26 100644
> > --- a/drivers/tty/serial/serial_core.c
> > +++ b/drivers/tty/serial/serial_core.c
> > @@ -1916,24 +1916,12 @@ static inline bool uart_console_enabled(struct uart_port *port)
> >  	return uart_console(port) && (port->cons->flags & CON_ENABLED);
> >  }
> >  
> > -static void __uart_port_spin_lock_init(struct uart_port *port)
> > +static void uart_port_spin_lock_init(struct uart_port *port)
> >  {
> >  	spin_lock_init(&port->lock);
> >  	lockdep_set_class(&port->lock, &port_lock_key);
> >  }
> >  
> > -/*
> > - * Ensure that the serial console lock is initialised early.
> > - * If this port is a console, then the spinlock is already initialised.
> > - */
> > -static inline void uart_port_spin_lock_init(struct uart_port *port)
> > -{
> 
> > -	if (uart_console(port))
> 
> I'm wondering if we may revert this line to be uart_console_enabled() and use a
> helper below twice.

I didn't do that on purpose as the rationale for why the
uart_console_enabled() check is there is different in the two paths so
merging the two comments, and moving it away from the call sites, wasn't
really a good idea to begin with.

> > -		return;
> > -
> > -	__uart_port_spin_lock_init(port);
> > -}
> > -
> >  #if defined(CONFIG_SERIAL_CORE_CONSOLE) || defined(CONFIG_CONSOLE_POLL)
> >  /**
> >   *	uart_console_write - write a console message to a serial port
> > @@ -2086,7 +2074,15 @@ uart_set_options(struct uart_port *port, struct console *co,
> >  	struct ktermios termios;
> >  	static struct ktermios dummy;
> >  
> > -	uart_port_spin_lock_init(port);
> > +	/*
> > +	 * Ensure that the serial-console lock is initialised early.
> > +	 *
> > +	 * Note that the console-enabled check is needed because of kgdboc,
> > +	 * which can end up calling uart_set_options() for an already enabled
> > +	 * console via tty_find_polling_driver() and uart_poll_init().
> > +	 */
> > +	if (!uart_console_enabled(port) && !port->console_reinit)
> > +		uart_port_spin_lock_init(port);
> >  
> >  	memset(&termios, 0, sizeof(struct ktermios));
> >  
> > @@ -2794,10 +2790,12 @@ static ssize_t console_store(struct device *dev,
> >  		if (oldconsole && !newconsole) {
> >  			ret = unregister_console(uport->cons);
> >  		} else if (!oldconsole && newconsole) {
> > -			if (uart_console(uport))
> > +			if (uart_console(uport)) {
> > +				uport->console_reinit = 1;
> >  				register_console(uport->cons);
> > -			else
> > +			} else {
> >  				ret = -ENOENT;
> > +			}
> >  		}
> >  	} else {
> >  		ret = -ENXIO;
> > @@ -2898,7 +2896,7 @@ int uart_add_one_port(struct uart_driver *drv, struct uart_port *uport)
> >  	 * initialised.
> >  	 */
> >  	if (!uart_console_enabled(uport))
> > -		__uart_port_spin_lock_init(uport);
> > +		uart_port_spin_lock_init(uport);
> >  
> >  	if (uport->cons && uport->dev)
> >  		of_console_check(uport->dev->of_node, uport->cons->name, uport->line);
> > diff --git a/include/linux/serial_core.h b/include/linux/serial_core.h
> > index 01fc4d9c9c54..8a99279a579b 100644
> > --- a/include/linux/serial_core.h
> > +++ b/include/linux/serial_core.h
> > @@ -248,6 +248,7 @@ struct uart_port {
> >  
> >  	unsigned char		hub6;			/* this should be in the 8250 driver */
> >  	unsigned char		suspended;
> > +	unsigned char		console_reinit;
> >  	const char		*name;			/* port name */
> >  	struct attribute_group	*attr_group;		/* port specific attributes */
> >  	const struct attribute_group **tty_groups;	/* all attributes (serial core use only) */
> > -- 
> > 2.26.2

Johan

Re: [PATCH 2/2] serial: core: fix console port-lock regression

[Andy Shevchenko]

+Cc: Tony, let me add Tony to the discussion.

On Thu, Sep 10, 2020 at 09:35:27AM +0200, Johan Hovold wrote:
> On Wed, Sep 09, 2020 at 06:48:15PM +0300, Andy Shevchenko wrote:
> > On Wed, Sep 09, 2020 at 04:31:01PM +0200, Johan Hovold wrote:
> > > Fix the port-lock initialisation regression introduced by commit
> > > a3cb39d258ef ("serial: core: Allow detach and attach serial device for
> > > console") by making sure that the lock is again initialised during
> > > console setup.
> > > 
> > > The console may be registered before the serial controller has been
> > > probed in which case the port lock needs to be initialised during
> > > console setup by a call to uart_set_options(). The console-detach
> > > changes introduced a regression in several drivers by effectively
> > > removing that initialisation by not initialising the lock when the port
> > > is used as a console (which is always the case during console setup).
> > > 
> > > Add back the early lock initialisation and instead use a new
> > > console-reinit flag to handle the case where a console is being
> > > re-attached through sysfs.
> > > 
> > > The question whether the console-detach interface should have been added
> > > in the first place is left for another discussion.
> > 
> > It was discussed in [1]. TL;DR: OMAP would like to keep runtime PM available
> > for UART while at the same time we disable it for kernel consoles in
> > bedb404e91bb.
> > 
> > [1]: https://lists.openwall.net/linux-kernel/2018/09/29/65
> 
> Yeah, I remember that. My fear is just that the new interface opens up a
> can of worms as it removes the earlier assumption that the console would
> essentially never be deregistered without really fixing all those
> drivers, and core functions, written under that assumption. Just to
> mention a few issues; we have drivers enabling clocks and other
> resources during console setup which can now be done repeatedly,

The series introduced the console ->exit() callback, so it should be easy to
fix.

>	and
> several drivers whose setup callbacks are marked __init and will oops
> the minute you reattach the console.

I believe this can be fixed relatively easy. As a last resort it can be a quirk
that disables console detachment for problematic consoles.

> And what about power management
> which was the reason for wanting this on OMAP in the first place; tty
> core never calls shutdown() for a console port, not even when it's been
> detached using the new interface.

That is interesting... Tony, do we have OMAP case working because of luck?

> I know, the console setup is all a mess, but this still seems a little
> rushed to me. I'm even inclined to suggest a revert until the above and
> similar issues have been addressed properly rather keeping a known buggy
> interface.

You know that it will be a dead end. Any solution how to move forward?

> > > Note that the console-enabled check in uart_set_options() is not
> > > redundant because of kgdboc, which can end up reinitialising an already
> > > enabled console (see commit 42b6a1baa3ec ("serial_core: Don't
> > > re-initialize a previously initialized spinlock.")).

-- 
With Best Regards,
Andy Shevchenko

Re: [PATCH 2/2] serial: core: fix console port-lock regression

[Johan Hovold]

On Thu, Sep 10, 2020 at 12:27:15PM +0300, Andy Shevchenko wrote:
> +Cc: Tony, let me add Tony to the discussion.
> 
> On Thu, Sep 10, 2020 at 09:35:27AM +0200, Johan Hovold wrote:
> > On Wed, Sep 09, 2020 at 06:48:15PM +0300, Andy Shevchenko wrote:
> > > On Wed, Sep 09, 2020 at 04:31:01PM +0200, Johan Hovold wrote:
> > > > Fix the port-lock initialisation regression introduced by commit
> > > > a3cb39d258ef ("serial: core: Allow detach and attach serial device for
> > > > console") by making sure that the lock is again initialised during
> > > > console setup.
> > > > 
> > > > The console may be registered before the serial controller has been
> > > > probed in which case the port lock needs to be initialised during
> > > > console setup by a call to uart_set_options(). The console-detach
> > > > changes introduced a regression in several drivers by effectively
> > > > removing that initialisation by not initialising the lock when the port
> > > > is used as a console (which is always the case during console setup).
> > > > 
> > > > Add back the early lock initialisation and instead use a new
> > > > console-reinit flag to handle the case where a console is being
> > > > re-attached through sysfs.
> > > > 
> > > > The question whether the console-detach interface should have been added
> > > > in the first place is left for another discussion.
> > > 
> > > It was discussed in [1]. TL;DR: OMAP would like to keep runtime PM available
> > > for UART while at the same time we disable it for kernel consoles in
> > > bedb404e91bb.
> > > 
> > > [1]: https://lists.openwall.net/linux-kernel/2018/09/29/65
> > 
> > Yeah, I remember that. My fear is just that the new interface opens up a
> > can of worms as it removes the earlier assumption that the console would
> > essentially never be deregistered without really fixing all those
> > drivers, and core functions, written under that assumption. Just to
> > mention a few issues; we have drivers enabling clocks and other
> > resources during console setup which can now be done repeatedly,
> 
> The series introduced the console ->exit() callback, so it should be
> easy to fix.

I'm not saying it's necessarily hard, I'm suggesting it should have been
considered before merging. But there could still be complications as the
console have always been considered a special case that's been hacked
around.

> >	and
> > several drivers whose setup callbacks are marked __init and will oops
> > the minute you reattach the console.
> 
> I believe this can be fixed relatively easy. As a last resort it can
> be a quirk that disables console detachment for problematic consoles.

Sure, but just removing the __init without vetting the drivers and
testing the new interface may not be much better than letting them oops.

> > And what about power management
> > which was the reason for wanting this on OMAP in the first place; tty
> > core never calls shutdown() for a console port, not even when it's been
> > detached using the new interface.
> 
> That is interesting... Tony, do we have OMAP case working because of luck?
> 
> > I know, the console setup is all a mess, but this still seems a little
> > rushed to me. I'm even inclined to suggest a revert until the above and
> > similar issues have been addressed properly rather keeping a known buggy
> > interface.
> 
> You know that it will be a dead end. Any solution how to move forward?

I guess that depends on how broken this is. I only gave a few examples
of the top of my head of issues that needs to be considered. 

But if this is to stay then making the feature opt-in by only exposing
the attribute for console drivers that implement the new exit() callback
or some other serial-driver flag might work.

Johan

Re: [PATCH 2/2] serial: core: fix console port-lock regression

[Tony Lindgren]

* Andy Shevchenko <andriy.shevchenko@linux.intel.com> [200910 09:27]:
> +Cc: Tony, let me add Tony to the discussion.
> 
> On Thu, Sep 10, 2020 at 09:35:27AM +0200, Johan Hovold wrote:
> > And what about power management
> > which was the reason for wanting this on OMAP in the first place; tty
> > core never calls shutdown() for a console port, not even when it's been
> > detached using the new interface.
> 
> That is interesting... Tony, do we have OMAP case working because of luck?

8250_omap won't do anything unless autosuspend_timeout is configured for
the uart(s). If configured, then the 8250_omap will idle when console is
detached and the PM runtime usage count held by console is decremented, and
the configured autosuspend_timeout expires.

The console is still kept open by getty, so I don't see why shutdown() would
be called for the console port. But maybe I don't follow what you're
concerned about, let me know if you want me to check something :)

Regards,

Tony

Re: [PATCH 2/2] serial: core: fix console port-lock regression

[Andy Shevchenko]

On Mon, Sep 14, 2020 at 11:09:16AM +0300, Tony Lindgren wrote:
> * Andy Shevchenko <andriy.shevchenko@linux.intel.com> [200910 09:27]:
> > +Cc: Tony, let me add Tony to the discussion.
> > 
> > On Thu, Sep 10, 2020 at 09:35:27AM +0200, Johan Hovold wrote:
> > > And what about power management
> > > which was the reason for wanting this on OMAP in the first place; tty
> > > core never calls shutdown() for a console port, not even when it's been
> > > detached using the new interface.
> > 
> > That is interesting... Tony, do we have OMAP case working because of luck?
> 
> 8250_omap won't do anything unless autosuspend_timeout is configured for
> the uart(s). If configured, then the 8250_omap will idle when console is
> detached and the PM runtime usage count held by console is decremented, and
> the configured autosuspend_timeout expires.
> 
> The console is still kept open by getty, so I don't see why shutdown() would
> be called for the console port. But maybe I don't follow what you're
> concerned about, let me know if you want me to check something :)

Is it possible to test configuration when you have kernel console enabled but
no getty is run on it (perhaps something with ssh enabled access)?

Then kernel console should call ->shutdown on detaching, right?

-- 
With Best Regards,
Andy Shevchenko

Re: [PATCH 2/2] serial: core: fix console port-lock regression

[Tony Lindgren]

* Andy Shevchenko <andriy.shevchenko@linux.intel.com> [200916 12:34]:
> On Mon, Sep 14, 2020 at 11:09:16AM +0300, Tony Lindgren wrote:
> > * Andy Shevchenko <andriy.shevchenko@linux.intel.com> [200910 09:27]:
> > > +Cc: Tony, let me add Tony to the discussion.
> > > 
> > > On Thu, Sep 10, 2020 at 09:35:27AM +0200, Johan Hovold wrote:
> > > > And what about power management
> > > > which was the reason for wanting this on OMAP in the first place; tty
> > > > core never calls shutdown() for a console port, not even when it's been
> > > > detached using the new interface.
> > > 
> > > That is interesting... Tony, do we have OMAP case working because of luck?
> > 
> > 8250_omap won't do anything unless autosuspend_timeout is configured for
> > the uart(s). If configured, then the 8250_omap will idle when console is
> > detached and the PM runtime usage count held by console is decremented, and
> > the configured autosuspend_timeout expires.
> > 
> > The console is still kept open by getty, so I don't see why shutdown() would
> > be called for the console port. But maybe I don't follow what you're
> > concerned about, let me know if you want me to check something :)
> 
> Is it possible to test configuration when you have kernel console enabled but
> no getty is run on it (perhaps something with ssh enabled access)?
> 
> Then kernel console should call ->shutdown on detaching, right?

I gave this a quick try and Johan is right, shutdown is not called on console
uart still even if detached and no getty running on that uart. I could not
figure out easily where exactly this gets blocked.. So far I did try setting
port->console = 0 on detach, then init it again on attach.

Regards,

Tony