Re: Pinmux bindings proposal

[Thomas Abraham <thomas.abraham-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>]

On 20 January 2012 23:23, Tony Lindgren <tony-4v6yS6AI5VpBDgjK7y7TUQ@public.gmane.org> wrote:
> * Thomas Abraham <thomas.abraham-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org> [120120 16:45]:
>> On 20 January 2012 15:35, Tony Lindgren <tony-4v6yS6AI5VpBDgjK7y7TUQ@public.gmane.org> wrote:
>> > * Thomas Abraham <thomas.abraham-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org> [120119 10:05]:
>> >> On 19 January 2012 23:50, Tony Lindgren <tony-4v6yS6AI5VpBDgjK7y7TUQ@public.gmane.org> wrote:
>> >>
>> >> 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?
>> >
>> > Hmm I see. Yes it's still needed as we only want to parse the DT once
>> > because it's slower unless it was one time only configuration during
>> > init.
>>
>> Ok. The time spent on searching for the pin-config property can be
>> reduced by having the device driver (say, i2c) keep a pointer to all
>> the pinconfig properties in its node. The next time a driver needs to
>> reconfigure the pins, the search time can be reduced. The time to
>> parse the property values though would still be applicable. But I
>> would still not opt to build pinmux/pinconfig/pindesc tables from dt.
>
> Hmm that's something to consider to save memory as the node will stay
> there. This would allow making all the pinctrl framework data __initdata
> in some cases. You'd probably want to copy the data into the driver in
> some pinctrl framework struct so you could still use pinctrl framework
> functions with this data and not have to parse the node again.

Is it required to use pinctrl functions when we already have the
hardware register values for pinmux/pinconfig in the device nodes? I
was of the opinion that we need not use pinctrl API in case of dt
based boot.

>
> For building the tables from dt, what I have currently is building
> the tables without any specific knowledge about the pinmux functions.
> I'm thinking that any further knowledge for debugging etc can be done
> later on using user space tools to avoid storing the data in kernel.
>

Ok. I will go through your patches when you post them.

Thanks,
Thomas.