On Tue, May 12, 2015 at 9:38 PM, Gregory Fong [off-list ref] wrote:

On Tue, May 12, 2015 at 3:59 AM, Linus Walleij [off-list ref] wrote:

quoted

On Wed, May 6, 2015 at 10:37 AM, Gregory Fong [off-list ref] wrote:

quoted

There is only one IRQ for each GIO IP block (i.e. several register banks share
an IRQ).  After briefly looking into the generic IRQ chip implementation, it
seemed like in this case that using it would result in the driver being more
complex than necessary because AFAICT it expects a 1:1 mapping of
irq_chip_generic to gpio_chip.  It seemed like less of a pain to have a single
irq_chip since we have a single IRQ for all register banks (multiple
gpio_chips).  I might be missing something, maybe using a shared IRQ across
multiple irq_chips is easier than I think?  Suggestions welcome.

What is needed is a 1:1 mapping between GPIO offsets and IRQ
offsets.

If you just number your GPIOs 0...n and your IRQs 0...n
it should work just fine with one irqchip for all banks.

What screws things up is likely that the hardware supports
32 lines per bank and not all are used.

I suggest you enable 32 line and 32 IRQs per bank,
so that hwirq maps nicely 1:1 on the GPIO offsets,
then just use the width thing to NACK operations on
GPIO lines you are not using. This way you can also
decode and warn on spurious IRQs on the unused lines.

For having 32 lines per bank, the big problem here is the upper limit
of 256 GPIOs.

Which arch is this?
Usually this limit comes from
arch/*/include/asm/gpio.h

For ARM that was bumped to 512 a while back. It is also possible
to define a custom value for your system by defining
ARCH_NR_GPIOS

Anyway, I don't think I understand IRQ domains and irq_chip_generic
very well.  One possibility _might_ be to use multiple irq_chips.

That is probably not possible if there is just one IRQ for all
banks.

The task of the irqdomain is a 1-to-1 translation from one
hardware numberspace to the Linux IRQ number space.

In your case the hardware IRQ (hwirq) numberspace
should be:

bank0: 0..31
bank1: 32..63
....
bankn: 32*n..32*n+31

I think the gpiolib irqchip code can translate that properly
as it is just a simple 0...x mapping, the irq handler need
some magic to loop over all banks from 0..n though.

Yours,
Linus Walleij