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.
v3: https://lore.kernel.org/r/20230327-tegra-pmic-reboot-v3-0-3c0ee3567e14@skida... v2: https://lore.kernel.org/all/20230320220345.1463687-1-bbara93@gmail.com/ system_state: https://lore.kernel.org/all/20230320213230.1459532-1-bbara93@gmail.com/ v1: https://lore.kernel.org/all/20230316164703.1157813-1-bbara93@gmail.com/
v4: - 1,2: add "Fixes" and adapt commit messages - 4: reduce delay after requesting the restart (as suggested by Dmitry)
v3: - bring system_state back in this series - do atomic i2c xfer if not preemptible (as suggested by Dmitry) - fix style issues mentioned by Dmitry - add cc stable as suggested by Dmitry - add explanation why this is needed for Jon
v2: - use devm-based restart handler - convert the existing power_off handler to a devm-based handler - handle system_state in extra series
--- Benjamin Bara (4): kernel/reboot: emergency_restart: set correct system_state i2c: core: run atomic i2c xfer when !preemptible mfd: tps6586x: use devm-based power off handler mfd: tps6586x: register restart handler
drivers/i2c/i2c-core.h | 2 +- drivers/mfd/tps6586x.c | 45 +++++++++++++++++++++++++++++++++++++-------- kernel/reboot.c | 1 + 3 files changed, 39 insertions(+), 9 deletions(-) --- base-commit: 197b6b60ae7bc51dd0814953c562833143b292aa change-id: 20230327-tegra-pmic-reboot-4175ff814a4b
Best regards,
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);
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 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)
On Thu, Apr 13, 2023 at 09:46:40AM +0200, 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 Signed-off-by: Benjamin Bara benjamin.bara@skidata.com
So, with Peter's input and me checking again:
Acked-by: Wolfram Sang wsa@kernel.org
I assume this shall go in via the mfd-tree. Let me know if I should pick it instead.
linux-stable-mirror@lists.linaro.org
-
Benjamin Bara -
Wolfram Sang