Re: [PATCH v7 2/5] i2c: core: run atomic i2c xfer when !preemptible

[Chris Morgan <macroalpha82@gmail.com>]

On Sat, Jul 15, 2023 at 09:53:24AM +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>
> Acked-by: Wolfram Sang <wsa@kernel.org>
> Reviewed-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
> Tested-by: Nishanth Menon <nm@ti.com>
> Signed-off-by: Benjamin Bara <benjamin.bara@skidata.com>

For kernel 6.7 I'm having an issue when I shutdown or reboot my
Rockchip RK3326 or Rockchip RK3566 based devices, and I've bisected
the issue down to this specific commit.

When I shutdown or restart the device, I receive messages in the kernel
log like the following:

[   37.121148] rk3x-i2c fdd40000.i2c: irq in STATE_IDLE, ipd = 0x3
[   37.122178] rk3x-i2c fdd40000.i2c: irq in STATE_IDLE, ipd = 0x3
[   37.123212] rk3x-i2c fdd40000.i2c: irq in STATE_IDLE, ipd = 0x3
[   37.124226] rk3x-i2c fdd40000.i2c: irq in STATE_IDLE, ipd = 0x3
[   37.125242] rk3x-i2c fdd40000.i2c: irq in STATE_IDLE, ipd = 0x3
[   37.126133] rk3x-i2c fdd40000.i2c: irq in STATE_IDLE, ipd = 0x1

The device will also occasionally freeze instead of rebooting or
shutting down. The i2c errors are consistent, but the freezing
behavior is not.

Thank you.

> ---
>  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
>