Re: [PATCH v7 4/4] pinctrl: qcom: Don't clear pending interrupts when enabling

[Stephen Boyd <swboyd@chromium.org>]

Quoting Douglas Anderson (2021-01-14 19:16:24)
> In Linux, if a driver does disable_irq() and later does enable_irq()
> on its interrupt, I believe it's expecting these properties:
> * If an interrupt was pending when the driver disabled then it will
>   still be pending after the driver re-enables.
> * If an edge-triggered interrupt comes in while an interrupt is
>   disabled it should assert when the interrupt is re-enabled.
> 
> If you think that the above sounds a lot like the disable_irq() and
> enable_irq() are supposed to be masking/unmasking the interrupt
> instead of disabling/enabling it then you've made an astute
> observation.  Specifically when talking about interrupts, "mask"
> usually means to stop posting interrupts but keep tracking them and
> "disable" means to fully shut off interrupt detection.  It's
> unfortunate that this is so confusing, but presumably this is all the
> way it is for historical reasons.
> 
> Perhaps more confusing than the above is that, even though clients of
> IRQs themselves don't have a way to request mask/unmask
> vs. disable/enable calls, IRQ chips themselves can implement both.
> ...and yet more confusing is that if an IRQ chip implements
> disable/enable then they will be called when a client driver calls
> disable_irq() / enable_irq().
> 
> It does feel like some of the above could be cleared up.  However,
> without any other core interrupt changes it should be clear that when
> an IRQ chip gets a request to "disable" an IRQ that it has to treat it
> like a mask of that IRQ.
> 
> In any case, after that long interlude you can see that the "unmask
> and clear" can break things.  Maulik tried to fix it so that we no
> longer did "unmask and clear" in commit 71266d9d3936 ("pinctrl: qcom:
> Move clearing pending IRQ to .irq_request_resources callback"), but it
> only handled the PDC case and it had problems (it caused
> sc7180-trogdor devices to fail to suspend).  Let's fix.
> 
> From my understanding the source of the phantom interrupt in the
> were these two things:
> 1. One that could have been introduced in msm_gpio_irq_set_type()
>    (only for the non-PDC case).
> 2. Edges could have been detected when a GPIO was muxed away.
> 
> Fixing case #1 is easy.  We can just add a clear in
> msm_gpio_irq_set_type().
> 
> Fixing case #2 is harder.  Let's use a concrete example.  In
> sc7180-trogdor.dtsi we configure the uart3 to have two pinctrl states,
> sleep and default, and mux between the two during runtime PM and
> system suspend (see geni_se_resources_{on,off}() for more
> details). The difference between the sleep and default state is that
> the RX pin is muxed to a GPIO during sleep and muxed to the UART
> otherwise.
> 
> As per Qualcomm, when we mux the pin over to the UART function the PDC
> (or the non-PDC interrupt detection logic) is still watching it /
> latching edges.  These edges don't cause interrupts because the
> current code masks the interrupt unless we're entering suspend.
> However, as soon as we enter suspend we unmask the interrupt and it's
> counted as a wakeup.
> 
> Let's deal with the problem like this:
> * When we mux away, we'll mask our interrupt.  This isn't necessary in
>   the above case since the client already masked us, but it's a good
>   idea in general.
> * When we mux back will clear any interrupts and unmask.
> 
> Fixes: 4b7618fdc7e6 ("pinctrl: qcom: Add irq_enable callback for msm gpio")
> Fixes: 71266d9d3936 ("pinctrl: qcom: Move clearing pending IRQ to .irq_request_resources callback")
> Signed-off-by: Douglas Anderson <dianders@chromium.org>
> Reviewed-by: Maulik Shah <mkshah@codeaurora.org>
> Tested-by: Maulik Shah <mkshah@codeaurora.org>
> ---

Reviewed-by: Stephen Boyd <swboyd@chromium.org>