Re: [PATCH V2] media: i2c: Add ADV761X support

[Valentine <valentine.barshak@cogentembedded.com>]

On 11/29/2013 02:45 PM, Lars-Peter Clausen wrote:
> On 11/29/2013 11:37 AM, Linus Walleij wrote:
>> On Wed, Nov 27, 2013 at 5:40 PM, Laurent Pinchart
>> <laurent.pinchart@ideasonboard.com> wrote:
>>> (CC'ing Linus Walleij, Wolfram Sang and LAKML)
>>> On Wednesday 27 November 2013 16:32:01 Valentine wrote:
>>>> On 11/27/2013 04:14 PM, Hans Verkuil wrote:
>>
>>>>> Yes, of course. Although the adv7604 has two interrupt lines, so if you
>>>>> would want to use the second, then that would still have to be specified
>>>>> through the platform data.
>>>>
>>>> In this case the GPIO should be configured as interrupt source in the
>>>> platform code. But this doesn't seem to work with R-Car GPIO since it is
>>>> initialized later, and the gpio_to_irq function returns an error.
>>>> The simplest way seemed to use a GPIO number in the platform data
>>>> to have the adv driver configure the pin and request the IRQ.
>>>> I'm not sure how to easily defer I2C board info IRQ setup (and
>>>> camera/subdevice probing) until GPIO driver is ready.
>>>
>>> Good question. This looks like a core problem to me, not specific to the
>>> adv761x driver. Linus, Wolfram, do you have a comment on that ?
>>
>> So we recently has a large-ish discussion involving me, Stephen
>> Warren and Jean-Christophe, leading to the conclusion that the
>> gpio_chip and irq_chip abstractions are orthogonal, and you should
>> be able to request a GPIO or IRQ without interacting with the other
>> subsystem.
>>
>> Specifically you should be able to request an IRQ from the irq_chip
>> portions of the driver without first requesting the GPIO line.
>>
>> Some drivers already support this.
>>
>> We added an internal API to the gpiolib so that the lib, *internally*
>> can be made aware that a certain GPIO line is used for IRQs,
>> see commit d468bf9ecaabd3bf3a6134e5a369ced82b1d1ca1
>> "gpio: add API to be strict about GPIO IRQ usage"
>>
>> So I guess the answer to the question is something like, fix
>> the GPIO driver to stop requiring the GPIO lines to be requested
>> and configured before being used as IRQs, delete that code,
>> and while you're at it add a call to gpiod_lock_as_irq()
>> to your GPIO driver in the right spot: examples are on the
>> mailing list and my mark-irqs branch in the GPIO tree.
>
> As far as I understand it this already works more or less with the driver.
> The problem is that the IRQ numbers are dynamically allocated, while the
> GPIO numbers apparently are not. So the board code knows the the GPIO number
> at compile time and can pass this to the diver which then does a gpio_to_irq
> to lookup the IRQ number.

This is correct.

> This of course isn't really a problem with
> devicetree, but only with platform board code.

I'm not sure what's the difference here and why it is not a problem with devicetree?

The other problem with R-Car GPIO driver is that it apparently does not support level IRQs.

>
> - Lars
>

Thanks,
Val.