On Thu, Mar 19, 2015 at 04:39:50PM +0100, Ludovic Desroches wrote:
> Hi,
>
> I would like to start a discussion about pinmuxing and device tree bindings.
>
> I am currently writing a new pinmuxing driver using the generic pinconf.
> My main concern is about defining functions and which pins belong to a
> group.
>
> At the moment, it seems that most drivers using the generic pinconf
> define this stuff in a static way. The pinctrl-at91 driver covers many
> devices, the new one should do the same for new Atmel devices. Having
> the group and function definitions in the driver could involve a huge
> file...
> I am not sure it is a good thing to embed all these information into a
> single zImage...
>
> How can we achieved this? I was thinking about something like this:
>
> pinctrl@fc06a000 {
>
> [...]
>
> pinctrl_defs {
> mci0 {
> mci0_ioset0_1bit_grp {
> at91,pins = <68 69 70>;
> at91,mux = <2>;
> };
>
> mci0_ioset0_4bit_grp {
> at91,pins = <68 69 70 71 72 73>;
> at91,mux = <2>;
> };
>
> mci0_ioset0_8bit_grp {
> at91,pins = <68 69 70 71 72 73 74 75 76 77>;
> at91,mux = <2>;
> };
> };
> };
Why are different groups here? Do you want to put them into the dtsi?
This would mean you have to carry a lot of groups in each dtsi from
which only a small fraction is used. We did that on i.MX but no longer
do this since the dtbs get very big.
>
> pinctrl_mci0_default: mci0_default {
> mux {
> function = "mci0";
> groups = &mci0_ioset0_8bit_grp;
> };
>
> conf {
> groups = &mci0_ioset0_8bit_grp;
> bias-pullup;
> };
> };
> };
>
> - A subnode for these definitions in order to not parse the whole
> pinctrl node to retrieve groups and functions.
> - Using node names as function and group names.
> - Can we get generic properties to define the groups? Of course a 'pins'
> property is mandatory. In my case I will need an extra one to tell the
> controller how to mux the pins (a same pin can have up to 7 muxing
> possibilities).
Did you have a look at the RFC I sent for these kind of controllers [1] and
the final result for the Mediatek driver currently in Linux-next [2]?.
The binding has both the config and the pins in a single node and thus
is very compact.
Sascha
[1]
http://lists.infradead.org/pipermail/linux-arm-kernel/2014-October/296491.html
[2]
http://lists.infradead.org/pipermail/linux-arm-kernel/2015-January/318452.html
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