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

[Y Vo]

On Mon, Sep 14, 2015 at 9:47 PM, Arnd Bergmann <arnd at arndb.de> wrote:
> On Monday 14 September 2015 16:39:43 Y Vo wrote:
>> On Mon, Sep 14, 2015 at 4:11 PM, Arnd Bergmann <arnd at arndb.de> wrote:
>> > On Saturday 12 September 2015 12:55:55 Y Vo wrote:
>> >> 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:
>> >>
>> >> 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>;
>> >>                 };
>> >>         };
>> >
>> > Wait, this looks wrong: the gpio driver doesn't actually see
>> > the connection here and won't be able to configure the interrupt
>> > correctly. The interrupt is already owned by the gpio driver, so
>> > you cannot use it in the button node.
>>
>> In summary:
>> - Our GPIO doesn't support interrupt controller.
>> - There are 6 pins which used the external interrupt from GIC, so all
>> setup for those irqs are from gic driver. The GPIO driver only
>> configure to wire those lines.
>>
>> For your concern:
>> - That's correct: if we use that defined, the gpio driver never saw
>> the connection here (That's why it already is configued at the
>> beginning).
>> - At the first time, we tried to use the define: <&sbgpio 13 1>, it
>> means using the GPIO_DS13, it will go into the GPIO driver to setup,
>> but there is another problem which I have sent out to all of you:
>> + It will go into gpio_keys_setup_key (gpio_keys.c driver) function,
>> then set the irqflags = IRQF_TRIGGER_RISING | IRQF_TRIGGER_FALLING,
>> but the gic only support IRQ_TYPE_LEVEL_HIGH && IRQF_TRIGGER_RISING,
>> so it always returns failed at gpio_keys_setup_key function. Please
>> see the gic_set_type at gic driver.
>
> Hmm, I see now how the event handling in the gpio-keys driver differs
> between irq mode and gpio mode, where gpio mode relies on getting
> a separate event for the release. This is certainly something that
> could be changed in the gpio-keys driver as an extension, but that
> seems to be what Laxman Dewangan did when he introduced the irq-mode.
>
>> static int gic_set_type(struct irq_data *d, unsigned int type)
>> {
>>         void __iomem *base = gic_dist_base(d);
>>         unsigned int gicirq = gic_irq(d);
>>
>>         /* Interrupt configuration for SGIs can't be changed */
>>         if (gicirq < 16)
>>                 return -EINVAL;
>>
>>         /* SPIs have restrictions on the supported types */
>>         if (gicirq >= 32 && type != IRQ_TYPE_LEVEL_HIGH &&
>>                             type != IRQ_TYPE_EDGE_RISING)
>>                 return -EINVAL;
>>
>>         return gic_configure_irq(gicirq, type, base, NULL);
>> }
>> + Another issue: in order gpio_key works it needs the status of GPIO.
>> For our chip, when the GPIO is configued as interrupt, we need to
>> access to GIC register to read the real status, it is not acceptable
>> to implement accessing GIC registers at gpio driver. The function
>> irq_get_irqchip_state(..) also doesn't work in our chip too. Because
>> it needs to access different offset.
>
> I thought we had solved that problem long ago when you first
> submitted the driver.
>
> Did 1b7047edfcfb25 ("genirq: Allow the irqchip state of an IRQ to be
> save/restored") not address the problem for you? You were on
> Cc to that patch and should have spoken up when the code that was
> merged was not sufficient.

Yes, I am in this mail-list too, but I also had a issue on this, I
think you are still in my submitted for this.
Currently, irq_get|set_irqchip_state(..) supports access to
GIC_DIST_ENABLE_SET, GIC_DIST_ACTIVE_SET, GIC_DIST_PENDING_SET. But
our hw only has the valid value at SPISR register ("[PATCH v4 2/3]
irqchip: GIC: Add support for irq_{get,set}_irqchip_state"), so I
still can not use it.

>
>> >> > 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  ?
>> >
>> > Yes, that would be an option.
>> I will look into it.
>>
>> Is there possible if:
>> - Keep GPIO8..GPIO as interrupt by default.
>> - Anyone want to use these GPIO pins as GPIO, we will re-configure
>> them to GPIO mode ?
>
> That's not perfect but better than the patch you sent here.
> The main disadvantage is that you end up with two references
> to the same IRQ. It can still work, but only as long as nothing
> tries to walk the entire DT to parse all the interrupts properties.
>
Let me think how.

> It would be ok for gpio-keys, as that does not need both the state
> and the event together, but for other gpio users, you still need a
> working driver that supports reading the state and getting an
> interrupt.
>
In irq mode, if I reconfigured that gpio pin to gpio mode, then
reading -> the value is valid.
Could I do that way badly ? It means switch to gpio mode to read
value, then switch back to  irq mode.


>         Arnd