AST SOC gpio pass-through support

[Yong Li]

Hi Andrew,

Thanks for your quick response. For device tree, I was thinking no
need to change/modify the device driver codes, it maybe simpler than
runtime pinmux(Changing code)? Anyway, I will compare all these
possible methods.

If there is any question, I will consult you again.

Thanks again!
Yong

2017-08-10 20:11 GMT+08:00 Andrew Jeffery <andrew at aj.id.au>:
> On Thu, 2017-08-10 at 18:55 +0800, Yong Li wrote:
>> Hi Andrew,
>>
>> I am thinking about "DYNAMIC DEVICE TREE". Maybe we can use it to
>> change the gpio pass-through dynamically?
>
> I feel you're barking up the wrong (device!) tree here. It might work
> in the end, but I expect you would be better off going with the runtime
> pinmuxing or bind/unbind than invoking the complexity of dynamic
> devicetrees.
>
>>
>> Let me study on these docs
>
> Feel free to keep me in the loop.
>
> Cheers,
>
> Andrew
>
>>
>> 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/lin
>> > > > ux.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