[PATCH v6 0/5] mfd: tps6586x: register restart handler

[PATCH v6 0/5] mfd: tps6586x: register restart handler

[Benjamin Bara]

Hi!

The Tegra20 requires an enabled VDE power domain during startup. As the
VDE is currently not used, it is disabled during runtime.
Since 8f0c714ad9be, there is a workaround for the "normal restart path"
which enables the VDE before doing PMC's warm reboot. This workaround is
not executed in the "emergency restart path", leading to a hang-up
during start.

This series implements and registers a new pmic-based restart handler
for boards with tps6586x. This cold reboot ensures that the VDE power
domain is enabled during startup on tegra20-based boards.

Since bae1d3a05a8b, i2c transfers are non-atomic while preemption is
disabled (which is e.g. done during panic()). This could lead to
warnings ("Voluntary context switch within RCU") in i2c-based restart
handlers during emergency restart. The state of preemption should be
detected by i2c_in_atomic_xfer_mode() to use atomic i2c xfer when
required. Beside the new system_state check, the check is the same as
the one pre v5.2.

v5: https://lore.kernel.org/r/20230327-tegra-pmic-reboot-v5-0-ab090e03284d@skidata.com

v6:
- drop 4/6 to abort restart on unexpected failure (suggested by Dmitry)
- 4,5: fix comments in handlers (suggested by Lee)
- 4,5: same delay for both handlers (suggested by Lee)

v5:
- introduce new 3 & 4, therefore 3 -> 5, 4 -> 6
- 3: provide dev to sys_off handler, if it is known
- 4: return NOTIFY_DONE from sys_off_notify, to avoid skipping
- 5: drop Reviewed-by from Dmitry, add poweroff timeout
- 5,6: return notifier value instead of direct errno from handler
- 5,6: use new dev field instead of passing dev as cb_data
- 5,6: increase timeout values based on error observations
- 6: skip unsupported reboot modes in restart handler

---
Benjamin Bara (5):
      kernel/reboot: emergency_restart: set correct system_state
      i2c: core: run atomic i2c xfer when !preemptible
      kernel/reboot: add device to sys_off_handler
      mfd: tps6586x: use devm-based power off handler
      mfd: tps6586x: register restart handler

 drivers/i2c/i2c-core.h |  2 +-
 drivers/mfd/tps6586x.c | 55 ++++++++++++++++++++++++++++++++++++++++++--------
 include/linux/reboot.h |  3 +++
 kernel/reboot.c        |  4 ++++
 4 files changed, 55 insertions(+), 9 deletions(-)
---
base-commit: 197b6b60ae7bc51dd0814953c562833143b292aa
change-id: 20230327-tegra-pmic-reboot-4175ff814a4b

Best regards,
-- 
Benjamin Bara <benjamin.bara@skidata.com>

[PATCH v6 1/5] kernel/reboot: emergency_restart: set correct system_state

[Benjamin Bara]

From: Benjamin Bara <benjamin.bara@skidata.com>

As the emergency restart does not call kernel_restart_prepare(), the
system_state stays in SYSTEM_RUNNING.

Since bae1d3a05a8b, this hinders i2c_in_atomic_xfer_mode() from becoming
active, and therefore might lead to avoidable warnings in the restart
handlers, e.g.:

[   12.667612] WARNING: CPU: 1 PID: 1 at kernel/rcu/tree_plugin.h:318 rcu_note_context_switch+0x33c/0x6b0
[   12.676926] Voluntary context switch within RCU read-side critical section!
...
[   12.742376]  schedule_timeout from wait_for_completion_timeout+0x90/0x114
[   12.749179]  wait_for_completion_timeout from tegra_i2c_wait_completion+0x40/0x70
...
[   12.994527]  atomic_notifier_call_chain from machine_restart+0x34/0x58
[   13.001050]  machine_restart from panic+0x2a8/0x32c

Avoid these by setting the correct system_state.

Fixes: bae1d3a05a8b ("i2c: core: remove use of in_atomic()")
Cc: stable@vger.kernel.org # v5.2+
Signed-off-by: Benjamin Bara <benjamin.bara@skidata.com>
---
 kernel/reboot.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/kernel/reboot.c b/kernel/reboot.c
index 3bba88c7ffc6..6ebef11c8876 100644
--- a/kernel/reboot.c
+++ b/kernel/reboot.c
@@ -74,6 +74,7 @@ void __weak (*pm_power_off)(void);
 void emergency_restart(void)
 {
 	kmsg_dump(KMSG_DUMP_EMERG);
+	system_state = SYSTEM_RESTART;
 	machine_emergency_restart();
 }
 EXPORT_SYMBOL_GPL(emergency_restart);

-- 
2.34.1

[PATCH v6 2/5] i2c: core: run atomic i2c xfer when !preemptible

[Benjamin Bara]

From: Benjamin Bara <benjamin.bara@skidata.com>

Since bae1d3a05a8b, i2c transfers are non-atomic if preemption is
disabled. However, non-atomic i2c transfers require preemption (e.g. in
wait_for_completion() while waiting for the DMA).

panic() calls preempt_disable_notrace() before calling
emergency_restart(). Therefore, if an i2c device is used for the
restart, the xfer should be atomic. This avoids warnings like:

[   12.667612] WARNING: CPU: 1 PID: 1 at kernel/rcu/tree_plugin.h:318 rcu_note_context_switch+0x33c/0x6b0
[   12.676926] Voluntary context switch within RCU read-side critical section!
...
[   12.742376]  schedule_timeout from wait_for_completion_timeout+0x90/0x114
[   12.749179]  wait_for_completion_timeout from tegra_i2c_wait_completion+0x40/0x70
...
[   12.994527]  atomic_notifier_call_chain from machine_restart+0x34/0x58
[   13.001050]  machine_restart from panic+0x2a8/0x32c

Use !preemptible() instead, which is basically the same check as
pre-v5.2.

Fixes: bae1d3a05a8b ("i2c: core: remove use of in_atomic()")
Cc: stable@vger.kernel.org # v5.2+
Suggested-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Acked-by: Wolfram Sang <wsa@kernel.org>
Signed-off-by: Benjamin Bara <benjamin.bara@skidata.com>
---
 drivers/i2c/i2c-core.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/i2c/i2c-core.h b/drivers/i2c/i2c-core.h
index 1247e6e6e975..05b8b8dfa9bd 100644
--- a/drivers/i2c/i2c-core.h
+++ b/drivers/i2c/i2c-core.h
@@ -29,7 +29,7 @@ int i2c_dev_irq_from_resources(const struct resource *resources,
  */
 static inline bool i2c_in_atomic_xfer_mode(void)
 {
-	return system_state > SYSTEM_RUNNING && irqs_disabled();
+	return system_state > SYSTEM_RUNNING && !preemptible();
 }
 
 static inline int __i2c_lock_bus_helper(struct i2c_adapter *adap)

-- 
2.34.1

Re: [PATCH v6 1/5] kernel/reboot: emergency_restart: set correct system_state

[Dmitry Osipenko]

On 5/9/23 22:02, Benjamin Bara wrote:
> From: Benjamin Bara <benjamin.bara@skidata.com>
> 
> As the emergency restart does not call kernel_restart_prepare(), the
> system_state stays in SYSTEM_RUNNING.
> 
> Since bae1d3a05a8b, this hinders i2c_in_atomic_xfer_mode() from becoming
> active, and therefore might lead to avoidable warnings in the restart
> handlers, e.g.:
> 
> [   12.667612] WARNING: CPU: 1 PID: 1 at kernel/rcu/tree_plugin.h:318 rcu_note_context_switch+0x33c/0x6b0
> [   12.676926] Voluntary context switch within RCU read-side critical section!
> ...
> [   12.742376]  schedule_timeout from wait_for_completion_timeout+0x90/0x114
> [   12.749179]  wait_for_completion_timeout from tegra_i2c_wait_completion+0x40/0x70
> ...
> [   12.994527]  atomic_notifier_call_chain from machine_restart+0x34/0x58
> [   13.001050]  machine_restart from panic+0x2a8/0x32c
> 
> Avoid these by setting the correct system_state.
> 
> Fixes: bae1d3a05a8b ("i2c: core: remove use of in_atomic()")
> Cc: stable@vger.kernel.org # v5.2+
> Signed-off-by: Benjamin Bara <benjamin.bara@skidata.com>
> ---
>  kernel/reboot.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/kernel/reboot.c b/kernel/reboot.c
> index 3bba88c7ffc6..6ebef11c8876 100644
> --- a/kernel/reboot.c
> +++ b/kernel/reboot.c
> @@ -74,6 +74,7 @@ void __weak (*pm_power_off)(void);
>  void emergency_restart(void)
>  {
>  	kmsg_dump(KMSG_DUMP_EMERG);
> +	system_state = SYSTEM_RESTART;
>  	machine_emergency_restart();
>  }
>  EXPORT_SYMBOL_GPL(emergency_restart);
> 

Reviewed-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>

-- 
Best regards,
Dmitry

Re: [PATCH v6 2/5] i2c: core: run atomic i2c xfer when !preemptible

[Dmitry Osipenko]

On 5/9/23 22:03, Benjamin Bara wrote:
> From: Benjamin Bara <benjamin.bara@skidata.com>
> 
> Since bae1d3a05a8b, i2c transfers are non-atomic if preemption is
> disabled. However, non-atomic i2c transfers require preemption (e.g. in
> wait_for_completion() while waiting for the DMA).
> 
> panic() calls preempt_disable_notrace() before calling
> emergency_restart(). Therefore, if an i2c device is used for the
> restart, the xfer should be atomic. This avoids warnings like:
> 
> [   12.667612] WARNING: CPU: 1 PID: 1 at kernel/rcu/tree_plugin.h:318 rcu_note_context_switch+0x33c/0x6b0
> [   12.676926] Voluntary context switch within RCU read-side critical section!
> ...
> [   12.742376]  schedule_timeout from wait_for_completion_timeout+0x90/0x114
> [   12.749179]  wait_for_completion_timeout from tegra_i2c_wait_completion+0x40/0x70
> ...
> [   12.994527]  atomic_notifier_call_chain from machine_restart+0x34/0x58
> [   13.001050]  machine_restart from panic+0x2a8/0x32c
> 
> Use !preemptible() instead, which is basically the same check as
> pre-v5.2.
> 
> Fixes: bae1d3a05a8b ("i2c: core: remove use of in_atomic()")
> Cc: stable@vger.kernel.org # v5.2+
> Suggested-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
> Acked-by: Wolfram Sang <wsa@kernel.org>
> Signed-off-by: Benjamin Bara <benjamin.bara@skidata.com>
> ---
>  drivers/i2c/i2c-core.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/i2c/i2c-core.h b/drivers/i2c/i2c-core.h
> index 1247e6e6e975..05b8b8dfa9bd 100644
> --- a/drivers/i2c/i2c-core.h
> +++ b/drivers/i2c/i2c-core.h
> @@ -29,7 +29,7 @@ int i2c_dev_irq_from_resources(const struct resource *resources,
>   */
>  static inline bool i2c_in_atomic_xfer_mode(void)
>  {
> -	return system_state > SYSTEM_RUNNING && irqs_disabled();
> +	return system_state > SYSTEM_RUNNING && !preemptible();
>  }
>  
>  static inline int __i2c_lock_bus_helper(struct i2c_adapter *adap)
> 

Reviewed-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>

-- 
Best regards,
Dmitry

Re: [PATCH v6 2/5] i2c: core: run atomic i2c xfer when !preemptible

[Nishanth Menon]

On 21:03-20230509, Benjamin Bara wrote:
> From: Benjamin Bara <benjamin.bara@skidata.com>
> 
> Since bae1d3a05a8b, i2c transfers are non-atomic if preemption is
> disabled. However, non-atomic i2c transfers require preemption (e.g. in
> wait_for_completion() while waiting for the DMA).
> 
> panic() calls preempt_disable_notrace() before calling
> emergency_restart(). Therefore, if an i2c device is used for the
> restart, the xfer should be atomic. This avoids warnings like:
> 
> [   12.667612] WARNING: CPU: 1 PID: 1 at kernel/rcu/tree_plugin.h:318 rcu_note_context_switch+0x33c/0x6b0
> [   12.676926] Voluntary context switch within RCU read-side critical section!
> ...
> [   12.742376]  schedule_timeout from wait_for_completion_timeout+0x90/0x114
> [   12.749179]  wait_for_completion_timeout from tegra_i2c_wait_completion+0x40/0x70
> ...
> [   12.994527]  atomic_notifier_call_chain from machine_restart+0x34/0x58
> [   13.001050]  machine_restart from panic+0x2a8/0x32c
> 
> Use !preemptible() instead, which is basically the same check as
> pre-v5.2.
> 
> Fixes: bae1d3a05a8b ("i2c: core: remove use of in_atomic()")
> Cc: stable@vger.kernel.org # v5.2+
> Suggested-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
> Acked-by: Wolfram Sang <wsa@kernel.org>
> Signed-off-by: Benjamin Bara <benjamin.bara@skidata.com>
> ---
>  drivers/i2c/i2c-core.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/i2c/i2c-core.h b/drivers/i2c/i2c-core.h
> index 1247e6e6e975..05b8b8dfa9bd 100644
> --- a/drivers/i2c/i2c-core.h
> +++ b/drivers/i2c/i2c-core.h
> @@ -29,7 +29,7 @@ int i2c_dev_irq_from_resources(const struct resource *resources,
>   */
>  static inline bool i2c_in_atomic_xfer_mode(void)
>  {
> -	return system_state > SYSTEM_RUNNING && irqs_disabled();
> +	return system_state > SYSTEM_RUNNING && !preemptible();
>  }
>  
>  static inline int __i2c_lock_bus_helper(struct i2c_adapter *adap)
> 
> -- 
> 2.34.1
> 
Tested-by: Nishanth Menon <nm@ti.com>

This in addition to a deeper bug in our driver seems to have helped
resolve a report we had been looking at. Tested on beagleplay platform

https://lore.kernel.org/all/ZGeHMjlnob2GFyHF@francesco-nb.int.toradex.com/

-- 
Regards,
Nishanth Menon
Key (0xDDB5849D1736249D) / Fingerprint: F8A2 8693 54EB 8232 17A3  1A34 DDB5 849D 1736 249D

Re: [PATCH v6 1/5] kernel/reboot: emergency_restart: set correct system_state

[Nishanth Menon]

On 21:02-20230509, Benjamin Bara wrote:
> From: Benjamin Bara <benjamin.bara@skidata.com>
> 
> As the emergency restart does not call kernel_restart_prepare(), the
> system_state stays in SYSTEM_RUNNING.
> 
> Since bae1d3a05a8b, this hinders i2c_in_atomic_xfer_mode() from becoming
> active, and therefore might lead to avoidable warnings in the restart
> handlers, e.g.:
> 
> [   12.667612] WARNING: CPU: 1 PID: 1 at kernel/rcu/tree_plugin.h:318 rcu_note_context_switch+0x33c/0x6b0
> [   12.676926] Voluntary context switch within RCU read-side critical section!
> ...
> [   12.742376]  schedule_timeout from wait_for_completion_timeout+0x90/0x114
> [   12.749179]  wait_for_completion_timeout from tegra_i2c_wait_completion+0x40/0x70
> ...
> [   12.994527]  atomic_notifier_call_chain from machine_restart+0x34/0x58
> [   13.001050]  machine_restart from panic+0x2a8/0x32c
> 
> Avoid these by setting the correct system_state.
> 
> Fixes: bae1d3a05a8b ("i2c: core: remove use of in_atomic()")
> Cc: stable@vger.kernel.org # v5.2+
> Signed-off-by: Benjamin Bara <benjamin.bara@skidata.com>
> ---
>  kernel/reboot.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/kernel/reboot.c b/kernel/reboot.c
> index 3bba88c7ffc6..6ebef11c8876 100644
> --- a/kernel/reboot.c
> +++ b/kernel/reboot.c
> @@ -74,6 +74,7 @@ void __weak (*pm_power_off)(void);
>  void emergency_restart(void)
>  {
>  	kmsg_dump(KMSG_DUMP_EMERG);
> +	system_state = SYSTEM_RESTART;
>  	machine_emergency_restart();
>  }
>  EXPORT_SYMBOL_GPL(emergency_restart);
> 
> -- 
> 2.34.1
> 

Tested-by: Nishanth Menon <nm@ti.com>

This in addition to a deeper bug in our driver seems to have helped
resolve a report we had been looking at. Tested on beagleplay platform

https://lore.kernel.org/all/ZGeHMjlnob2GFyHF@francesco-nb.int.toradex.com/

-- 
Regards,
Nishanth Menon
Key (0xDDB5849D1736249D) / Fingerprint: F8A2 8693 54EB 8232 17A3  1A34 DDB5 849D 1736 249D

Re: [PATCH v6 1/5] kernel/reboot: emergency_restart: set correct system_state

[Francesco Dolcini]

Hello Nishanth,

On Wed, Jun 14, 2023 at 07:06:50PM -0500, Nishanth Menon wrote:
> On 21:02-20230509, Benjamin Bara wrote:
> > From: Benjamin Bara <benjamin.bara@skidata.com>
> > 
> > As the emergency restart does not call kernel_restart_prepare(), the
> > system_state stays in SYSTEM_RUNNING.
> > 
> > Since bae1d3a05a8b, this hinders i2c_in_atomic_xfer_mode() from becoming
> > active, and therefore might lead to avoidable warnings in the restart
> > handlers, e.g.:
> > 
> > [   12.667612] WARNING: CPU: 1 PID: 1 at kernel/rcu/tree_plugin.h:318 rcu_note_context_switch+0x33c/0x6b0
> > [   12.676926] Voluntary context switch within RCU read-side critical section!
> > ...
> > [   12.742376]  schedule_timeout from wait_for_completion_timeout+0x90/0x114
> > [   12.749179]  wait_for_completion_timeout from tegra_i2c_wait_completion+0x40/0x70
> > ...
> > [   12.994527]  atomic_notifier_call_chain from machine_restart+0x34/0x58
> > [   13.001050]  machine_restart from panic+0x2a8/0x32c
> > 
> > Avoid these by setting the correct system_state.
> > 
> > Fixes: bae1d3a05a8b ("i2c: core: remove use of in_atomic()")
> > Cc: stable@vger.kernel.org # v5.2+
> > Signed-off-by: Benjamin Bara <benjamin.bara@skidata.com>
> > ---
> >  kernel/reboot.c | 1 +
> >  1 file changed, 1 insertion(+)
> > 
> > diff --git a/kernel/reboot.c b/kernel/reboot.c
> > index 3bba88c7ffc6..6ebef11c8876 100644
> > --- a/kernel/reboot.c
> > +++ b/kernel/reboot.c
> > @@ -74,6 +74,7 @@ void __weak (*pm_power_off)(void);
> >  void emergency_restart(void)
> >  {
> >  	kmsg_dump(KMSG_DUMP_EMERG);
> > +	system_state = SYSTEM_RESTART;
> >  	machine_emergency_restart();
> >  }
> >  EXPORT_SYMBOL_GPL(emergency_restart);
> > 
> > -- 
> > 2.34.1
> > 
> 
> Tested-by: Nishanth Menon <nm@ti.com>
> 
> This in addition to a deeper bug in our driver seems to have helped
> resolve a report we had been looking at. Tested on beagleplay platform
> 
> https://lore.kernel.org/all/ZGeHMjlnob2GFyHF@francesco-nb.int.toradex.com/

Is this patch going to fix the RCU warning I reported on that email or
it is just part of a more complex solution?

Francesco

Re: [PATCH v6 1/5] kernel/reboot: emergency_restart: set correct system_state

[Nishanth Menon]

On 15:21-20230615, Francesco Dolcini wrote:
> > > 
> > > -- 
> > > 2.34.1
> > > 
> > 
> > Tested-by: Nishanth Menon <nm@ti.com>
> > 
> > This in addition to a deeper bug in our driver seems to have helped
> > resolve a report we had been looking at. Tested on beagleplay platform
> > 
> > https://lore.kernel.org/all/ZGeHMjlnob2GFyHF@francesco-nb.int.toradex.com/
> 
> Is this patch going to fix the RCU warning I reported on that email or
> it is just part of a more complex solution?

From what I see, It is part of the solution.
Problem happens as follows for us:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/firmware/ti_sci.c#n421

When i2c is not that frequently used, runtime pm disables the power
domain on our platform. As part of reset or power-off, when i2c is
invoked, it ends up calling into the firmware handler which (no
surprise), attempts to do the wrong thing (and rightly flagged by RCU).

We are in the middle of trying various combinations out to ensure we
are'nt messing things up.

-- 
Regards,
Nishanth Menon
Key (0xDDB5849D1736249D) / Fingerprint: F8A2 8693 54EB 8232 17A3  1A34 DDB5 849D 1736 249D