[PATCH 2/2] Documentation: gpio: Update description for X-Gene standby GPIO controller DTS binding

[Y Vo]

On Fri, Sep 11, 2015 at 11:45 PM, Arnd Bergmann <arnd at arndb.de> wrote:
> On Friday 11 September 2015 22:06:58 Y Vo wrote:
>> On Fri, Sep 11, 2015 at 9:47 PM, Arnd Bergmann <arnd at arndb.de> wrote:
>> > On Friday 11 September 2015 21:23:31 Y Vo wrote:
>> >> Is that possible if we change to this approach:
>> >> - Keep all GPIO as GPIO mode by default.
>> >> - If anyone want to use them as interrupt, they must add the interrupt
>> >> node to DT specific-board below:
>> >>
>> >> Example to configure GPIO_DS11, 12, 13 as external irq:
>> >>
>> >> &sbgpio {
>> >>         interrupts = <0x0 0x2b 0x1>,         /* GPIO_DS11 */
>> >>                         <0x0 0x2c 0x1>,         /* GPIO_DS12 */
>> >>                         <0x0 0x2d 0x1>;         /* GPIO_DS13 */
>> >
>> > That is exactly the same as you have in your patch. You should
>> > always list all interrupts that the gpio controller is wired
>> > to, whether they are used or not.
>> >
>> > Ideally, the driver just decides at runtime how to wire that
>> > mux, based on how the gpio is configured by the client driver.
>> > If the client asks for an interrupt (with gpio_to_irq) and is
>> > it is configured as an input, then you connect it to the GIC,
>> > otherwise you leave it to be handled by the gpio chip itself.
>> > Any reason you can't do that?
>> >
>> As I just explained, the GPIO Standby doesn't support the interrupt.
>> Both interrupts are came from GIC, so if the client asks for an
>> interrupt, it will go to the GIC driver (not GPIO Standby driver), so
>> that's my trouble. We can not implement the code to configured the
>> GPIO standby at GIC driver.
>
> So you are saying we merged a binding that is incapable of describing
> the hardware? If that is the case, we may have to go back to
> the drawing board and come up with a working binding.
>
> One part that I don't understand yet is how the driver handles
> irqs to start with, as it does not register a nested irq domain
> or irqchip, so I'm guessing that client drivers cannot actually
> use the IRQ functionality. Is that right?
For our case the irq_domain is in irq-gic driver, the GPIO driver only
is responsible to wire 2 the external irq of GIC to GPIO pin.

Example for configure GPIO_DS13 as interrupt and use as button with
the current gpio driver:
        gpio-keys {
                compatible = "gpio-keys";
                button at 1 {
                        label = "POWER";
                        linux,code = <116>;
                        linux,input-type = <0x1>;
                        interrupts = <0x0 0x2d 0x1>;
                };
        };

>
> It also seems to me that the binding cannot distinguish between a
> line configured as an input and one that is configured as an
> interrupt, which are for other gpio chips the same thing, but
> not on this one.  Could this be rectified by using another bit
> of the second gpio cell? The low bit is used for active-high/active-low,
> so you could use the second bit for irq/input.
>
Do you mean #gpio-cells property and using the high bit of the second
bit for irq/input  ?

>         Arnd