CVE-2026-74468: gpio: pch: use raw_spinlock_t for the register lock

In the Linux kernel, the following vulnerability has been resolved:

gpio: pch: use rawspinlockt for the register lock

pchirqtype() is registered as the irqchip .irqsettype callback and takes chip->spinlock with spinlockirqsave(). This callback is reached from setupirq() -> irqsettrigger() -> chip->irqsettype() while the caller holds desc->lock, a rawspinlockt, with hardirqs disabled. That context is not sleepable, but on PREEMPTRT a regular spinlockt is an rtmutex-backed sleeping lock, so acquiring it there is invalid.

This was confirmed on a PREEMPTRT kernel with lockdep (PROVERAWLOCKNESTING and DEBUGATOMICSLEEP). A grounded PoC mirrored pchirqtype()'s locking and drove it through the real genirq carrier irqsetirqtype() -> irqsettrigger() -> chip->irqsettype(), i.e. the same irqsettrigger() edge that setupirq() takes for a requested IRQ. With the original spinlockirqsave() edge lockdep reported an invalid wait context, immediately followed by:

BUG: sleeping function called from invalid context at kernel/locking/spinlockrt.c:48 inatomic(): 1, irqsdisabled(): 1, nonblock: 0, pid: 95, name: insmod hardirqs last disabled at (3784): rawspinlockirqsave+0x4f/0x60 rtspinlock+0x3a/0x1c0 reproirqsettype+0x64/0xa0 [pchrepro] irqsettrigger+0x69/0x140 irqsetirqtype+0x78/0xd0

Switching the mirrored lock to rawspinlockt made both splats go away.

Convert the register lock to rawspinlockt. The same lock also serializes the GPIO direction/value callbacks and the suspend/resume register save/restore, but all of those critical sections only perform MMIO register accesses (ioread32()/iowrite32()) and irqsethandlerlocked(); none of them contain sleepable operations. Keeping this register lock non-sleeping is therefore appropriate for the irqchip callbacks and does not change the GPIO-side locking contract.

This is the same class of issue and fix as recently addressed for other GPIO controllers, e.g. commit 286533cb14a3 ("gpio: sch: use rawspinlockt in the irq startup path") and commit 90f0109019e6 ("gpio: eic-sprd: use rawspinlockt in the irq startup path").