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
--
To unsubscribe from this list: send the line "unsubscribe linux-gpio" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
