genirq: ipipe: protect generic chip against domain preemption
As described in Documentation/ipipe.rst, irq_chip drivers need to be specifically adapted for dealing with interrupt pipelining safely. The basic issue to address is proper serialization between some irq_chip handlers which may be called from out-of-band context immediately upon receipt of an IRQ, and the rest of the driver which may access the same data / IO registers from the regular - in-band - context on the same CPU. This commit converts the generic irq_chip lock to a hard spinlock, which ensures such serialization.
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