Messages in this thread | | | Date | Wed, 24 Jan 2018 14:07:05 +0100 | From | Ludovic Desroches <> | Subject | Re: [RFC PATCH 2/2] gpio: provide a consumer when requesting a gpio |
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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: > > > > > It can be useful for the pinmuxing layer to know which device is > > > requesting a GPIO. Add a consumer variant for gpiod_request to > > > reach this goal. > > > > > > GPIO chips managed by pin controllers should provide the new > > > request_consumer operation. They can rely on > > > gpiochip_generic_request_consumer instead of > > > gpiochip_generic_request. > > > > > > Signed-off-by: Ludovic Desroches <ludovic.desroches@microchip.com> > > > > 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? > > > > It's the probably the way to go, it was Maxime's proposal and Andy seems > to agree this solution. >
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:
- 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.
> > I.e. in that case you just allow gpio_owner to proceed and take the > > pin just like with a non-strict controller.
Regards
Ludovic
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