Messages in this thread | | | From | Andy Shevchenko <> | Date | Wed, 24 Jan 2018 17:42:15 +0200 | Subject | Re: [RFC PATCH 2/2] gpio: provide a consumer when requesting a gpio |
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On Wed, Jan 24, 2018 at 3:07 PM, Ludovic Desroches <ludovic.desroches@microchip.com> wrote: > On Thu, Jan 18, 2018 at 04:22:28PM +0100, Ludovic Desroches wrote: >> On Thu, Jan 18, 2018 at 11:30:00AM +0100, Linus Walleij wrote: >> > On Mon, Jan 15, 2018 at 5:24 PM, Ludovic Desroches >> > <ludovic.desroches@microchip.com> wrote:
>> > I think we need to think over what is a good way to share ownership >> > of a pin. >> > >> > Russell pointed me to a similar problem incidentally and I briefly looked >> > into it: there are cases when several devices may need to hold the >> > same pin. >> > >> > Can't we just look up the associated gpio_chip from the GPIO range, >> > and in case the pin is connected between the pin controller and >> > the GPIO chip, then we allow the gpiochip to also take a >> > reference?
How do you find my proposal about introducing ownership level (not requested yet; exclusive; shared)?
>> It's the probably the way to go, it was Maxime's proposal and Andy seems >> to agree this solution.
Confirm with caveat that this is a fix for subset of cases.
> If pin_request() is called with gpio_range not NULL, it means that the > requests comes from a GPIO chip and the pin controller handles this pin. > In this case, I would say the pin is connected between the pin > controller and the GPIO chip. Is my assumption right? > > I am not sure it will fit all the cases:
I think it doesn't cover cases when you have UART + UART + GPIO (I posted early a use case example).
But at least it doesn't move things in a wrong direction.
> - case 1: device A requests the pin (pinctrl-default state) and mux it > as a GPIO. Later,it requests the pin as a GPIO (gpiolib). This 'weird' > situation happens because some strict pin controllers were not declared > as strict and/or pinconf is needed. > > - case 2: device A requests the pin (pinctrl-default state). Device B > requests the pin as a GPIO (gpiolib). > > In case 1, pin_request must not return an error. In case 2, pin_request > must return an error even if the pin is connected between the pin > controller and the GPIO chip.
For these cases looks OK to me.
>> > I.e. in that case you just allow gpio_owner to proceed and take the >> > pin just like with a non-strict controller.
-- With Best Regards, Andy Shevchenko
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