Re: Pinconf issues on AMxxx plattforms

[Tony Lindgren <tony@atomide.com>]

* Linus Walleij <linus.walleij@linaro.org> [230504 08:31]:
> On Thu, May 4, 2023 at 7:35 AM Tony Lindgren <tony@atomide.com> wrote:
> > * Niedermayr, BENEDIKT <benedikt.niedermayr@siemens.com> [230503 08:38]:
> 
> > > We encountered some issues when accessing the gpiochardev interface on an
> > > AM65xx plaform.
> 
> Thank you for using contemporary APIs!
> 
> > > The pinctrl offers 3 different options for muxing:
> > >
> > > 1.  Using the generic kernel APIs:
> > >      Call pinctrl_select_state() function as stated
> > > in  Documentation/driver-api/pin-control.rst (section "Pin control requests
> > > from drivers").
> > >      This function will select a defined state which has been defined in DTB
> > > with "pinctrl-0", "pinctrl-1", "pinctrl-x"
> > > 2.  Mux pins with debugfs:
> > >      Write the desired pingroup and pinfunction into the "pinmux-select"
> > > file of the related pin controller.
> > > 3. Mux the GPIO function of a requested GPIO pin by calling the pinctrl
> > > drivers pcs_request_gpio() function.
> > >
> > > The problem now is that only option 1. will store the current mux
> > > information in the pinctrl subsystems core.
> > > The pinctrl-single driver highly depends on that information, which is not
> > > available at all wenn muxing with options 2&3.
> > >
> > > I was able to fix that for option 2 but not for option 3. The problem here
> > > is that the pcs_request_gpio() function just does not provide enough
> > > parameters with sufficient information for achieving that task.
> 
> The fact that 3) doesn't work has to do with how pinctrl-single has
> been engineered I think, what the pinctrl_ops .gpio_request_enable/
> .gpio_disable_free/.gpio_set_direction provide is a "shortcut"
> for drivers that want to take it, in case they can provide the right
> information.
> 
> The pinctrl-single driver only implements .gpio_request_enable()
> but often that is enough.
> 
> Then it is the callbacks for generic config that you said you already
> added to gpio-davinci.c, so that part should be fine, patches welcome!

Thanks for explaining. Sounds like pinctrl-single should possibly
implement the missing functions and update pinctrl core with the
changes when a gpio is requested.

Regards,

Tony