From: Ben Hutchings <redacted>
Date: Sun, 11 Jul 2010 04:12:34 +0100

But an interrupt handler will not be called recursively for the same
IRQ.  Since this device only uses one IRQ, surely it was OK to use
spin_lock() in this function so long as it was only called from the
interrupt handler.

It seems your right, I'll make a note about the real reason we're
doing this in the commit message.

But frankly anything else is dangerous.  Especially if one intends to
support ->poll_controller() which we pretty much expect every modern
and future driver to do.