Re: [PATCH] firmware: tegra: bpmp: Make atomic_tx_lock a raw_spinlock

[Sebastian Andrzej Siewior <bigeasy@linutronix.de>]

On 2026-05-05 15:47:23 [-0400], Waiman Long wrote:
>  __might_resched+0x254/0x330
>  rt_spin_lock+0x70/0x140
>  tegra_bpmp_transfer_atomic+0x118/0x3c0
>  tegra_bpmp_probe+0x564/0x6f0

So this is tegra_bpmp_ping().

> I know that interrupt is disabled becasue of the following code.
> 
> 346 int tegra_bpmp_transfer_atomic(struct tegra_bpmp *bpmp, 347 struct
> tegra_bpmp_message *msg) 348 { 349 struct tegra_bpmp_channel *channel; 350
> int err; 351 352 if (WARN_ON(!irqs_disabled())) 353 return -EPERM;

Well, yes. It disables interrupts just probably to document the time it
took for the transfer so it can write it then via dev_dbg().
It is hard to tell what the worst-case delay here is but it is probably
not important if this is just boot time/ driver probe. Maybe.
What I am bit more concerned if the actual path of this
tegra_bpmp_transfer_atomic() invocation via i2c driver is actually
invoked with disabled interrupts on PREEMPT_RT. Because that might not
be the case. I've been looking at the i2c call chain and it is not
obvious what the actual call chain is. There is just
i2c_in_atomic_xfer_mode() check. So it may or may not be used in the
end.

> Cheers, Longman

Sebastian