Re: [RFC PATCH 10/12] arm/tegra: Add device tree support to pinmux driver

[Jamie Iles <jamie-wmLquQDDieKakBO8gow8eQ@public.gmane.org>]

On Mon, Aug 15, 2011 at 01:44:53PM -0700, Stephen Warren wrote:
> Jamie Iles wrote at Monday, August 15, 2011 2:36 PM:
> > On Mon, Aug 15, 2011 at 09:07:16PM +0100, Jamie Iles wrote:
> > > Hi Stephen,
> > >
> > > On Fri, Aug 12, 2011 at 04:54:55PM -0600, Stephen Warren wrote:
> > > > Signed-off-by: Stephen Warren <swarren-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org>
> ...
> > > > diff --git a/arch/arm/mach-tegra/pinmux.c b/arch/arm/mach-tegra/pinmux.c
> ...
> > > > +static void __init tegra_pinmux_probe_dt(struct platform_device *pdev)
> > > > +{
> > > > +	int pg;
> > > > +
> > > > +	for (pg = 0; pg < TEGRA_MAX_PINGROUP; pg++) {
> > > > +		const char *pg_name = pingroup_name(pg);
> > > > +		struct tegra_pingroup_config config;
> > > > +		struct device_node *pg_node;
> > > > +		int ret;
> > > > +		const char *s;
> > > > +
> > > > +		pg_node = of_find_child_node_by_name(pdev->dev.of_node,
> > > > +						     pg_name);
> > > > +		if (pg_node == NULL)
> > > > +			continue;
> > > > +
> > > > +		config.pingroup = pg;
> > > > +
> > > > +		ret = of_property_read_string(pg_node, "nvidia,function", &s);
> ...
> > > > +		ret = of_property_read_string(pg_node, "nvidia,pull", &s);
> ...
> > > > +		if (of_find_property(pg_node, "nvidia,tristate", NULL))
> ...
> > > > +		tegra_pinmux_config_pingroup(&config);
> > > > +
> > > > +		of_node_put(pg_node);
> > > > +	}
> > > > +}
> > >
> > > I need to implement DT muxing configuration for my platform, and I believe
> > > that what you have here would work fine for me too, and to avoid duplicating
> > > the same thing, I wonder if this could be a little more generic.
> > >
> > > So if the platform specific pinmux driver called the pinmux parser with a
> > > callback for a pingroup configuration function then this wouldn't need the
> > > nvidia specific properties.  I'd envisage the setup callback to be something
> > > like:
> > >
> > > 	int pingroup_configure(const char *name, unsigned long flags);
> > 
> > and it if this took the device_node too then the platform specific bits could
> > handle more esoteric properties if required.  I'll have a go at prototyping
> > this tomorrow unless there are any obvious reasons that this is a stupid idea!
> 
> I expect some of the code could be shared.
> 
> The only worry I have is whether some SoCs don't configure things like
> pinmux function in the same place as pad function (pullup/down, tristate),
> and hence whether a generic binding is generally applicable. I suppose the
> code could always ignore unused properties.

Yes, well our hardware doesn't support any of these features other than 
setting the function so in the picoxcell backend I'd just WARN_ON() invalid 
flags settings.

> I wonder how much of this is relevant to Linus W's pinctrl API?

Hmm, not sure on that one, it's been a while since I've looked at Linus' 
patches.

> Note that in the updated patch series I just posted, I reworked the binding
> a little; Tegra has two sets of pin-groups, one configuring muxing, pullup/
> down, and tri-state, and the other configuring various driver strength/
> rate properties. Hence, the tree is now e.g.:
> 
> 	pinmux: pinmux@70000000 {
> 		compatible = "nvidia,tegra20-pinmux";
> 		reg = < 0x70000000 0xc00 >;
> 		nvidia,mux-groups {
> 			cdev1 {
> 				nvidia,function = "plla_out";
> 			};
> 			cdev2 {
> 				nvidia,function = "pllp_out4";
> 				nvidia,pull-down;
> 				nvidia,tristate;
> 			};
> 		};
> 		nvidia,drive-groups {
> 			sdio1 {
> 				nvidia,schmitt;
> 				nvidia,drive-power = <1>;
> 				nvidia,pull-down-strength = <31>;
> 				nvidia,pull-up-strength = <31>;
> 				nvidia,slew-rate-rising = <3>;
> 				nvidia,slew-rate-falling = <3>;
> 			};
> 		};
> 	};
> 
> But it's probably still reasonably easy to make the parser for the mux-groups
> node generic. Perhaps it makes sense for all SoCs to have a "mux-settings"
> node, even if they don't have any other custom nodes?

You have a much more complex chip than I do!  I don't know if *all* SoC's have 
to have the same muxing binding, but it feels that this one should cover a lot 
of the most common bases.

Jamie