When an external device generated a level based interrupt then the
interrupt controller could miss the interrupt. The reason is that the
interrupt controller can detect only link changes.

In the following example, if there is a PHY that generates an interrupt
then the following would happen. The GPIO detected that the interrupt
line changed, and then the 'ocelot_irq_handler' was called. Here it
detects which GPIO line saw the change and for that will call the
following:
1. irq_mask
2. phy interrupt routine
3. irq_eoi
4. irq_unmask

And this works fine for simple cases, but if the PHY generates many
interrupts, for example when doing PTP timestamping, then the following
could happen. Again the function 'ocelot_irq_handler' will be called
and then from here the following could happen:
1. irq_mask
2. phy interrupt routine
3. irq_eoi
4. irq_unmask

Right before step 3(irq_eoi), the PHY will generate another interrupt.
Now the interrupt controller will acknowledge the change in the
interrupt line. So we miss the interrupt.

A solution will be to use 'handle_level_irq' instead of
'handle_fasteoi_irq', because for this will change routine order of
handling the interrupt.
1. irq_mask
2. irq_ack
3. phy interrupt routine
4. irq_unmask

And now if the PHY will generate a new interrupt before irq_unmask, the
interrupt controller will detect this because it already acknowledge the
change in interrupt line at step 2(irq_ack).

But this is not the full solution because there is another issue. In
case there are 2 PHYs that share the interrupt line. For example phy1
generates an interrupt, then the following can happen:
1.irq_mask
2.irq_ack
3.phy0 interrupt routine
4.phy1 interrupt routine
5.irq_unmask

In case phy0 will generate an interrupt while clearing the interrupt
source in phy1, then the interrupt line will be kept down by phy0. So
the interrupt controller will not see any changes in the interrupt line.
The solution here is to update 'irq_unmask' such that it can detect if
the interrupt line is still active or not. And if it is active then call
again the procedure to clear the interrupts. But we don't want to do it
every time, only if we know that the interrupt controller has not seen
already that the interrupt line has changed.

While at this, add support also for IRQ_TYPE_LEVEL_LOW.

Fixes: be36abb7 ("pinctrl: ocelot: add support for interrupt controller")
Signed-off-by: Horatiu Vultur <horatiu.vultur@microchip.com>
Link: https://lore.kernel.org/r/20220909145942.844102-1-horatiu.vultur@microchip.comSigned-off-by: Linus Walleij <linus.walleij@linaro.org>