AST SOC gpio pass-through support

[Yong Li]

Hi Andrew,

I am thinking about "DYNAMIC DEVICE TREE". Maybe we can use it to
change the gpio pass-through dynamically?

Let me study on these docs

Thanks again!
Yong



2017-08-10 18:11 GMT+08:00 Andrew Jeffery <andrew at aj.id.au>:
> On Thu, 2017-08-10 at 17:01 +0800, Yong Li wrote:
>> thanks for your quick response Andrew!
>
> No worries!
>
>> i will read these info deeply. just a quick question, is it possible
>> to enable/disable the pass through dynamically after kernel boots?  how?
>
> So there is the concept of runtime pinmuxing[1]: It's possible for a
> device to have several pinmux states that can be configured/selected
> from process context. Alternatively, a naive approach might be just
> unbinding the driver for the device you used to select the pass-through
> mux function(s) - this would free up the pins to be requested as
> regular GPIOs. However, you'd need to request the mux on a device node
> other than the pinctrl node, as unbinding that would have undesirable
> consequences :)
>
> Hope that helps.
>
> Andrew
>
> [1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/driver-api/pinctl.rst#n1385
>
>>
>> > > > 在 2017年8月10日，16:28，Andrew Jeffery <andrew at aj.id.au> 写道：
>> >
>> > Hi Yong,
>> >
>> > > On Thu, 2017-08-10 at 15:50 +0800, Yong Li wrote:
>> > > Hi all,
>> >
>> > Welcome to the list!
>> >
>> > >
>> > > AST SOC supports GPIOE pass-through function, I would like to know if
>> > > the kernel provides such API/interface to enable/disable pass-through?
>> >
>> > Yes, the kernel's pinmux drivers can configure GPIO passthrough for
>> > you. In general, all the functions are documented in the pinctrl
>> > devicetree bindings:
>> >
>> >    https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/devicetree/bindings/pinctrl/pinctrl-aspeed.txt?h=v4.12
>> >
>> > Specifically, you are after functions/groups GPIE{0,2,4,6}. We already
>> > have these defined in the Aspeed DTSIs, so to configure them you can
>> > add something like the following snippet in your devicetree:
>> >
>> >    &pinctrl {
>> >            pinctrl-names = "default";
>> >            pinctrl-0 = <&pinctrl_gpie0_default
>> >                    &pinctrl_gpie2_default
>> >                    &pinctrl_gpie4_default
>> >                    &pinctrl_gpie6_default>;
>> >    }
>> >
>> > Specifying the mux configuration in the pinctrl node is probably as
>> > good a place as any, though if you have somewhere more relevant you
>> > should probably use that. Naturally you can remove any of these
>> > phandles to only select the specific pass-through configurations you
>> > need.
>> >
>> > If you want to pass-through the whole bank you can also set the board
>> > strapping to make it the case right from power-on. The strapping
>> > register *is* writeable, however the kernel's pinctrl driver treats it
>> > as read-only, as really, the system designer ought configure it either
>> > via pull-ups or in the boot firmware.
>> >
>> > The passthrough capability is a bit of an odd case - despite being GPIO
>> > I chose to represent it as a pinctrl function. Hope it makes sense to
>> > you.
>> >
>> > Cheers,
>> >
>> > Andrew