On Tue, 16 Feb 2021 11:16:03 +0900 William Breathitt Gray <vilhelm.gray@xxxxxxxxx> wrote: > 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 <vilhelm.gray@xxxxxxxxx> 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 <syednwaris@xxxxxxxxx> > > > Signed-off-by: William Breathitt Gray <vilhelm.gray@xxxxxxxxx> > > > > 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] But on RT setups the interrupts become threads and are preemptable etc, so that shouldn't matter. There are a few corner cases that cause trouble, but in most normal drivers you should be fine with a spin_lock. Jonathan > 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
