On Sun, Feb 14, 2021 at 06:19:46PM +0000, Jonathan Cameron wrote: > On Fri, 12 Feb 2021 21:13:45 +0900 > William Breathitt Gray <[email protected]> wrote: > > > This patch replaces the mutex I/O lock with a spinlock. This is in > > preparation for a subsequent patch adding IRQ support for 104-QUAD-8 > > devices; we can't sleep in an interrupt context, so we'll need to use a > > spinlock instead. > > > > Cc: Syed Nayyar Waris <[email protected]> > > Signed-off-by: William Breathitt Gray <[email protected]> > > Why do these need to be raw_spin_locks? > Normally only need to do that if in code related to interrupt chips etc, > not their use. > > Jonathan
This lock can be taken in an interrupt context in a subsequent patch: counter_push_event() called by quad8_irq_handler() can end up calling the Counter component callbacks which take this lock. We can't use a mutex nor a regular spinlock because those can sleep on RT setups [1] which would result in a deadlock due to the interrupt context here -- so therefore we're left with using raw_spin_lock. [1] https://lwn.net/Articles/367219/ William Breathitt Gray
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