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

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

On 2026-05-04 12:34:48 [-0400], Waiman Long wrote:
> The atomic_tx_lock was first introduced by commit 1abb081e41a7
> ("firmware: tegra: Simplify channel management") as a spinlock_t. It
> is used only in tegra_bpmp_transfer_atomic() to ensure mutual exclusion.
> 
> Since the merging of PREEMPT_RT support into mainline Linux kernel
> in v6.12, a spinlock becomes a sleeping lock when CONFIG_PREEMPT_RT
> is enabled. As tegra_bpmp_transfer_atomic() is called with interrupt
> disabled, acquiring a sleeping lock will lead to the following bug
> report when booting up a PREEMPT_RT kernel on an tegra based arm64
> system with Boot and Power Management Processor (BPMP).
> 
>   BUG: sleeping function called from invalid context at kernel/locking/spinlock_rt.c:48
>   in_atomic(): 0, irqs_disabled(): 1, non_block: 0, pid: 1, name: swapper/0
>   preempt_count: 0, expected: 0
>   RCU nest depth: 0, expected: 0
>   2 locks held by swapper/0/1:
>    #0: ffff42bda2d5b0f0 (&dev->mutex){....}-{3:3}, at: __driver_attach+0x110/0x2c0
>    #1: ffff42bda4da5138 (&bpmp->atomic_tx_lock){....}-{2:2}, at: tegra_bpmp_transfer_atomic+0x118/0x3c0
> 
> Fix it by changing the type of atomic_tx_lock in the tegra_bpmp structure
> to raw_spinlock_t and use raw_spinlock APIs to access it.

Do you have a backtrace why interrupts are disabled to begin with?

Sebastian