Pinmux bindings proposal

[Thomas Abraham]

On 19 January 2012 23:50, Tony Lindgren <tony at atomide.com> wrote:
> * Thomas Abraham <thomas.abraham at linaro.org> [120119 09:05]:
>>
>> On 19 January 2012 22:26, Tony Lindgren <tony at atomide.com> wrote:
>> > * Thomas Abraham <thomas.abraham at linaro.org> [120119 04:37]:
>> >>
>> >> i2c0: i2c at 18000000 {
>> >>         [... other properties ...]
>> >>         pinctrl-active = <&pctrl0 5 0 2 3 0>,
>> >>                              <&pctrl0 5 1 2 3 0>;
>> >>         pinctrl-suspend = <&pctrl0 5 0 2 0 0>,
>> >>                                 <&pctrl0 5 1 2 0 0>;
>> >> };
>> >
>> > Maybe we should have just the active/suspend/off flags in the
>> > same array? Otherwise we'll end up unnecessarily repeating the
>> > the pin information. See the pins + #pin-args example I posted,
>> > which is otherwise similar.
>>
>> Yes, I agree. That would be better.
>
> OK great.
>
>> >
>> >> In the example above, the specifier of pinctrl-* is specific for
>> >> Samsung io-pad controllers. Its format/syntax would be mainly
>> >> dependent on the io-pad controller used, the above is only an example
>> >> for Samsung io-pad controller. In the above node, the format of the
>> >> pinctrl-* specifier is
>> >>
>> >> property-name = <phandle of the pin-controller
>> >>                            pin bank within the pin-controller
>> >>                            pin number within the pin-bank
>> >>                            pin-mux function number
>> >>                            pull up/down config
>> >>                            drive strength config>;
>> >
>> > Are these all just bits in one register? If so, let's say you
>> > have 16-bits per pin, we might be able to share the generic
>> > pinmux-simple.c driver I have almost ready..
>>
>> no, these get written to different registers, one for pinmux, one for
>> pull up/down and one for drive strength. It would be helpful of your
>> pinmux-simple.c can support writes to multiple registers also.
>
> Hmm yeah that should be doable, and actually we have the old legacy
> omap1510 set up with three different registers per pin..
>
> The question is: Do we want to add the on/idle/off modes for each
> pin in .dts, or do we want to have the driver set the dynamic muxing
> flags separately?
>

It would be better to include the pin muxing and config options in the
node of a device. So a i2c device node would have pin mux and pin
config options listed in its node. But this means, each board dts file
would have to repeat this information. On the other hand, describing
mux and config options for each pin in a SoC dtsi file would be too
much of information. I would go with the first option.


>> > The format would then be
>> >
>> >        #pin-args <4>;
>> >        ...
>> >
>> >        /*    controller  offset on   idle off */
>> >        pins = <&pinctrl0 0x0030 0x15 0x15 0x7>;
>> >
>> >> * Using the pinmux/pinconfig specifier in device nodes to configure hardware.
>> >>
>> >> A driver (for a device instantiated from device tree) would require
>> >> code to be made aware of the pinmux/pinconfig options available. The
>> >> typical sequence in a probe function would be as below.
>> >>
>> >> (a) call of_get_named_gpio() to get the gpio number. In case of
>> >> Samsung pinctrl driver, the pinctrl driver itself provides the gpiolib
>> >> functionality and it attaches a gpio specifier translator with the
>> >> gpio_chip. This translator is capable of translating the pinctrl-* and
>> >> returning a gpio number.
>> >>
>> >> (b) gpio_request() the gpio number obtained in step (a) above.
>> >>
>> >> (c) Repeat steps (a) and (b) until all the gpios required by the
>> >> driver are requested. In case a request fails, give up all the
>> >> successfully requested gpio and return failure.
>> >
>> > Can't the driver do this to request the gpio pins that you
>> > can get from DT and pinmux? Even if you need to do dynamic pinmuxing
>> > to GPIO pins for wake-up events, you can do that from the driver
>> > as long as you get the GPIO number for the pin from mux code.
>>
>> Yes, it is the driver that finds out the gpio number from dt and
>> requests it. Maybe, I did not understand your point here.
>
> Oh ok, sorry I misunderstood thinking you want to do all that in the
> pinmux driver..
>
>> With the approach that I mentioned in the previous email, there are no
>> pinmux, pin groups or pin desc tables built from dt. Each device node
>> specifies what needs to configured (pinmux,pinconfig) and the code
>> using that device node uses pinctrl driver to get those
>> pinmux/pinconfig values written to the hardware registers.
>>
>> Does the dt support for pinmux/pinconfig that you are developing build
>> the pinmux, pin groups or pin desc tables? Do drivers have to call
>> pinmux_{get/put}() or pin_config_set() functions even in dt case?
>
> Yeah the pinmux/pingroups and functions are built from the DT. Drivers
> would have to still call pinmux_get and set right now. But some of this
> could probably be automatically done using runtime PM?
>

I would like to understand the need for populating the
pinmux/pingroups tables from dt. The question here is when we have
something like

pins = <&pinctrl0 0x0030 0x15 0x15 0x7>;

which specifies the values that need to be written to the hardware
registers, would populating pinmux/pingroup tables from dt required.
The SoC specific pinctrl driver can provide a way (with the help of
pinctrl core) to translate these values and write to corresponding
hardware registers. Is there any particular reason for populating the
pinmux/pingroups tables from dt?

Thanks,
Thomas.