Re: [RESEND PATCH] pinctrl: rockchip: Disable interrupt when changing it's capability

[JeffyChen]

Hi Brian,

On 05/08/2018 10:31 AM, JeffyChen wrote:
> Hi Brian,
>
> On 05/08/2018 09:56 AM, Brian Norris wrote:
> > On Tue, May 08, 2018 at 09:36:24AM +0800, Jeffy Chen wrote:
> > > On 05/08/2018 06:15 AM, Brian Norris wrote:
> > > > On the other hand...this also implies there may be a race condition
> > > > there, where we might lose an interrupt if there is an edge between the
> > > > re-configuration of the polarity in rockchip_irq_demux() and the
> > > > clearing/handling of the interrupt (handle_edge_irq() ->
> > > > chip->irq_ack()). If we have an edge between there, then we might ack
> > > > it, but leave the polarity such that we aren't ready for the next
> > > > (inverted) edge.
> > >
> > > if let me guess, the unexpected irq we saw is the hardware trying to
> > > avoid
> > > losing irq? for example, we set a EDGE_RISING, and the hardware saw
> > > the gpio
> > > is already high, then though it might lost an irq, so fake one for safe?
> >
> > I won't pretend to know what the IC designers were doing, but I don't
> > think that would resolve the problem I'm talking about. The sequence is
> > something like:
> > 1. EDGE_BOTH IRQ occurs (e.g., low to high)
> > 2. reconfigure polarity in rockchip_irq_demux() (polarity=low)
> > 3. continue to handle_edge_irq()
> > 4. another HW edge occurs (e.g., high to low)
> > 5. handle_edge_irq() (from 3) acks (clears) IRQ (before a subsequent
> >     rockchip_irq_demux() gets a chance to run and flip the polarity)
> > ...
> >
> > Now the polarity is still low, but the next trigger should be a
> > low-to-high edge.
>
> oops, i see the problem.
>
> so what if we do these:
> 1/ edge irq triggered
> 2/ read gpio level
> 3/ handle irq(ack irq)
> 4/ toggle edge mode(with a while gpio level check)
>
> if the gpio changed in 2/ -> 3/, the 4/ will trigger an irq when writing
> GPIO_INT_POLARITY(which is what we are trying to avoid in the set_type
> case)
>
> but this would not work if i'm wrong about how the HW fake an irq when
> changing POLARITY...
>
>
> or maybe we could just check the gpio status again after
> handle_edge_irq, and correct the polarity in this case

i saw the pinctrl-msm.c do this in the ack(),

and also at the end of set_type(), which might avoid another race in the 
set_type()

> > > i'll try to confirm it with IC guys.
> >
> > Brian