Re: [openbmc-kernel]: How to make pinctrl not affect pass-through function?

[Andrew Jeffery]

On Fri, 22 Nov 2019, at 14:55, www wrote:
> At 2019-11-22 08:31:05, "Andrew Jeffery" <andrew at aj.id.au> wrote:

*snip* 

> >Getting back to your problem rather than solutions, it's possible to view
> >this as a deficiency in the GPIO subsystem and Aspeed GPIO driver: If we
> >could describe that we want the pin muxed for pass-through as part of
> >the GPIO request then your problem would be partly resolved, save for 
> >the fact that the exported GPIO would still be read-only. However, that
> >issue is fully resolved by multiple sequential GPIO requests: export the
> >GPIO in pass-through mode initially, and then when it comes to changing
> >the host state, re-export the GPIO in non-pass-through mode so that it is
> >writable, and then again re-export the GPIO back in pass-through mode
> >after the host state change has been applied. This is the sequence of
> >your original solution above, just without the need for additional drivers
> >with ad-hoc userspace interfaces or introducing bugs into the pinctrl
> >driver.
> >What are your thoughts on this?
> >
> 
> I haven't heard of this way. Would you please explain it in detail? Thank you

What details are you after? What I suggested above is not yet possible -
we'd need to develop some kernel patches to make it work, but they would
be something we could upstream. pinctrl needs to remain aware of whether
a pin is in GPIO pass-through mode or not, as it not only affects how that pin
will behave but how *other* "unrelated" pins might behave as well.

Andrew