Messages in this thread | | | Date | Thu, 18 Feb 2021 19:16:08 +0900 | From | William Breathitt Gray <> | Subject | Re: [PATCH v8 21/22] counter: 104-quad-8: Replace mutex with spinlock |
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On Tue, Feb 16, 2021 at 07:27:20PM +0000, Jonathan Cameron wrote: > On Tue, 16 Feb 2021 11:16:03 +0900 > William Breathitt Gray <vilhelm.gray@gmail.com> 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@gmail.com> 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@gmail.com> > > > > Signed-off-by: William Breathitt Gray <vilhelm.gray@gmail.com> > > > > > > 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
Thinking this over again I realize you're probably right. A simple spin_lock should be fine for these drivers, so I'll switch over to that instead of the raw_spin_lock for this driver and the Counter interface code.
William Breathitt Gray
> > 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 > [unhandled content-type:application/pgp-signature] | |