Messages in this thread | | | From | Thomas Gleixner <> | Subject | Re: [PATCH] gpio: siox: indicate exclusive support of threaded IRQs | Date | Thu, 06 Aug 2020 20:50:45 +0200 |
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Linus Walleij <linus.walleij@linaro.org> writes: > On Thu, Aug 6, 2020 at 12:20 PM Thomas Gleixner <tglx@linutronix.de> wrote: > >> So the solution for this driver is either to make the dispatch handler >> threaded or use the hard interrupt variant of dispatching the >> demultiplexed GPIO interrupts. > > The struct gpio_irq_chip .threaded bool that the patch > sets just instructs the gpio core to issue > irq_set_nested_thread(irq, 1) on the child IRQ. > > This is a driver of type "struct siox_driver" handling the > IRQ through the special .get_data callback supplied in the > driver struct and it calls handle_nested_irq(irq) so with > this fix it percolated up to the parent as intended. > > So far so good. So I think the patch should be applied. > > But what is behind this .get_data() callback for siox drivers? > > The siox driver framework in drivers/siox dispatches calls > to .get_data() from a polling thread which is just some ordinary > kthread. It looks like this because the SIOX (I think) needs > to do polled I/O. (drivers/siox/siox-core.c) > > So this is a thread but it is not an irq thread from the irq core, > however it is treated like such by the driver, and in a way what > happens is events, just polled by a thread.
As Uwe just explained.
> So when we call handle_nested_irq() ... we are not really > calling that from an irq handler. > > I don't know if the IRQ core even sees a difference between which > thread it gets interfaced with. I suppose it does? :/
handle_nested_irq() does not care. It cares about thread context, external reentrancy protection for the same nested interrupt and that the nested interrupt has a thread handler.
The latter is what goes belly up because w/o that threaded bit set the GPIO core fails to set nested thread. So if a consumer requests an interrupt with request_any_context_irq() then that fails to select thread mode which means the threaded handler is not set causing handle_nested_irq() to fail.
The polling kthread is a slight but clever abomination, but it just works because it provides thread context and cannot run concurrently.
So Ahmad's patch is correct, just the changelog needs polishing.
Thanks,
tglx
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