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

[Y Vo]

On Fri, Sep 11, 2015 at 7:46 PM, Arnd Bergmann <arnd at arndb.de> wrote:
> On Friday 11 September 2015 18:24:47 Y Vo wrote:
>> On Fri, Sep 11, 2015 at 4:35 PM, Arnd Bergmann <arnd at arndb.de> wrote:
>> > On Friday 11 September 2015 16:22:12 Y Vo wrote:
>> >>  There are 20 GPIO pins from 0..21. There is no GPIO_DS14 or GPIO_DS15,
>> >> -only GPIO_DS8..GPIO_DS13 support interrupts. The IRQ mapping
>> >> +only GPIO_DS8..GPIO_DS13 support external interrupts. The IRQ mapping
>> >>  is currently 1-to-1 on interrupts 0x28 thru 0x2d.
>> >> +GPIO pins from GPIO_DS8 to GPIO_DS13 are configured as external interrupt
>> >> +by default. If one wish not to use any of these pins as external interrupts,
>> >> +the corresponding interrupt resource for those pins should be removed.
>> >
>> > According to this description, I fail to see how one would specify
>> > a missing interrupt for one of the pins that is not the last one in
>> > the list.
>> >
>> All GPIO_DS8..GPIO_DS13 are configured as external IRQ by default. So
>> if anyone want to use one of them as gpio mode, they can drop add the
>> sbgpio node to their DTB board-specific, and remove that GPIO from
>> interrupts property. As example below I want to leave GPIO_DS8 as gpio
>> mode, so I remove it as below:
>>
>> /* Board-specific: exclude GPIO_DS8 to leave it as GPIO */
>> &sbgpio {
>>        interrupts =    <0x0 0x29 0x1>,         /* GPIO_DS9 */
>>                        <0x0 0x2a 0x1>,         /* GPIO_DS10 */
>>                        <0x0 0x2b 0x1>,         /* GPIO_DS11 */
>>                        <0x0 0x2c 0x1>,         /* GPIO_DS12 */
>>                        <0x0 0x2d 0x1>;         /* GPIO_DS13 */
>> }
>
> This would be a very unusual binding, because that requires the driver
> to know the contents of the properties in advance and the driver
> cannot derive the function of an irq from the position in the array.
>
> Please come up with another approach that is more like other drivers
> do this and that makes it possible to reuse the driver if the
> interrupt numbers change.
The GPIO standby doesn't support interrupt controller itself, it only
wires the GPIO line to the external IRQ of GIC. So it is not similar
to other driver. Each GPIO is fixed to GIC IRQ index, and never
change.

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 */


>         Arnd