Subject: Pinmux bindings proposal V2

From: [email-masked] (Tony Lindgren)
Date: Mon, 23 Jan 2012 13:00:52 -0800

Hi,

This mostly looks pretty good to me, few more comments below.

* Stephen Warren <[email-masked]> [120120 13:51]:
> Here's V2 of my pinmux binding proposal, after incorporating some feedback
> from Shawn Guo and Dong Aisheng. Main changes:
> 
> 1) Require the "pin config" nodes the be children of the pinmux controller
>    node, rather than allowing them to alternatively be children of the
>    device node that's using them. This allows removal of the pin controller
>    phandle as the first entry in each specifier.

If you really want to leave out the phandle for each mux entry, this would
require supporting multiple "pin config" entries in a device driver node.

That's because otherwise supporting pins from multiple pinmux controller
instances would not work. Note that we already have two pin controller
instances starting with omap4.

...
 
>                 pmx_sdhci_active: pinconfig-sdhci-active {
>                         /*
>                          * In each of these nodes, both the mux and config
>                          * properties are optional. This node represents the
>                          * additions to pmx_sdhci that are specific to an
>                          * active state. In this case, only pin configuration
>                          * settings are different.
>                          */
>                         config =
>                                 <TEGRA_PMX_PG_DTA TEGRA_PMX_CONF_TRISTATE 0>
>                                 <TEGRA_PMX_PG_DTD TEGRA_PMX_CONF_TRISTATE 0>;
>                 };
>                 pmx_sdhci_standby: pinconfig-sdhci-standby {
>                         config =
>                                 <TEGRA_PMX_PG_DTA TEGRA_PMX_CONF_TRISTATE 1>
>                                 <TEGRA_PMX_PG_DTD TEGRA_PMX_CONF_TRISTATE 1>;
>                 };

After thinking about this a bit more, I'm now thinking that we should
probably only describe the active state in the device tree to keep things
simple.

Anything PM related could be initialized later on during the boot by the
device driver, or even from userspace using /lib/firmware or /sys entries.
This would cut down the device tree bloat quite a bit.

Setting the initial state from device tree makes sense, but I'm afraid
the standby and off states will require driver interaction depending on
how the user wants to configure the system.

For example, allowing a device to wake up a system might be user
configurable option, such as "Wake up on tapping the touchscreen".

Then I'd rather not use "config" at all, and just put the value for
initial state mux register(s) in the mux to avoid repeating the same data
multiple time. Looks like with the mux + config/mux-config option you
need to duplicate at least TEGRA_PMX_PG_DTA.

BTW, maybe the name "config" should probably be "mux-config" instead?

>                 /*
>                  * Each device node contains a few properties to describe
>                  * the named pinmux states that are available to it.
>                  *
>                  * The binding for the device node specifies the state names
>                  * that must be described; common examples such as "default"
>                  * or "active" and "suspend" may be universal, but the IO
>                  * protocol that a device supports may demand that more
>                  * states be defined, such as "active-12mhz", "active-50mhz",
>                  * "suspend". Drivers request these named states e.g. using
>                  * pinctrl's pinmux_get("state_name") API.
>                  *
>                  * pinctrl-names lists the available state names.
>                  *
>                  * Unlike the common clock binding, I assume here that states
>                  * are always requested by name. If we don't like that idea,
>                  * we'd could make this property optional, and add a new API
>                  * pinmux_get(state_id) to the pinctrl subsystem.
>                  */
>                 pinctrl-names = "active", "suspend";

If we only allow describing the initial state in device tree, then we can
leave out pinctrl-names, and assume the setting is always the initial bootup
state desired.

So to summarize: I suggest we'll just stick to basics to get the system
booting and devices working using device tree. In most cases the device
drivers should be able to configure the suspend and off states in a generic
way using pinctrl API. Everything else, like debugging, we can probably
do with userspace tools.

This would mean just using a minimal subset of your binding, probably
very close to what you originally suggested.

Regards,

Tony