[Buildroot] Random Linux/device tree/GPIO question posted to the wrong list...

[Thomas Petazzoni <thomas.petazzoni@bootlin.com>]

Hello Patrick,

On Tue, 31 Jul 2018 09:53:34 -0400, Patrick Doyle wrote:

> Thank you for the quick reply.  pinctrl_nand_default _is_ referenced
> by the device tree clause for the nand controller:
> 
>         nand0: nand at 80000000 {
>             nand-bus-width = <8>;
>             nand-ecc-mode = "hw";
>             nand-on-flash-bbt;
>             atmel,has-pmecc;
>             atmel,pmecc-cap = <12>;
>             atmel,pmecc-sector-size = <512>;
>             pinctrl-names = "default";
>             pinctrl-0 = <&pinctrl_nand_default &pinctrl_nand_rdy_en>;
>             status = "okay";
> ...
> 
> Hence my confusion.  Am I missing something else somewhere?

Asked internally, and my colleague Maxime Ripard (in Cc) gave some
explanation about this: it depends on whether the pinctrl driver uses
the strict mode or not and the Atmel doesn't.

This allows to request a pin as a GPIO even if this pin is already
muxed as a different functionality. Some details about this are
available at "GPIO mode pitfalls" in
https://www.kernel.org/doc/Documentation/driver-api/pinctl.rst (link
also provided by Maxime).

Best regards,

Thomas
-- 
Thomas Petazzoni, CTO, Bootlin (formerly Free Electrons)
Embedded Linux and Kernel engineering
https://bootlin.com