linux-kernel - Re: Pinmux bindings proposal

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Date:	Thu, 19 Jan 2012 02:57:28 -0800
From:	Tony Lindgren <tony@...mide.com>
To:	Stephen Warren <swarren@...dia.com>
Cc:	Grant Likely <grant.likely@...retlab.ca>,
	Dong Aisheng-B29396 <B29396@...escale.com>,
	"linus.walleij@...ricsson.com" <linus.walleij@...ricsson.com>,
	"s.hauer@...gutronix.de" <s.hauer@...gutronix.de>,
	"rob.herring@...xeda.com" <rob.herring@...xeda.com>,
	"kernel@...gutronix.de" <kernel@...gutronix.de>,
	"cjb@...top.org" <cjb@...top.org>,
	"Simon Glass (sjg@...omium.org)" <sjg@...omium.org>,
	Dong Aisheng <dongas86@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"devicetree-discuss@...ts.ozlabs.org" 
	<devicetree-discuss@...ts.ozlabs.org>
Subject: Re: Pinmux bindings proposal

* Stephen Warren <swarren@...dia.com> [120118 11:29]:
> Tony Lindgren wrote at Wednesday, January 18, 2012 7:13 AM:
> 
> I'd prefer not to do that for my platforms, for the reason Shawn points
> out in his reply to yours.
> 
> However, I believe the bindings I proposed are flexible enough to allow
> you to do exactly this for your platforms without requiring that everyone
> do it.

Well I can easily use one phandle per pinmux controller instance
instead of one phandle per pin, so let's plan on doing that.
 
> Recall my proposal was:

Yes I think that's pretty close to what I'm using, just few
minor comments below.
 
> pmx_sdhci_standby: pinctrl@0 {
>     /* Format is <&pmx_controller_phandle muxable_entity_id
>      * selected_function>.
>      */
>     mux =
>         <&tegra_pmx TEGRA_PMX_PG_DTA TEGRA_PMX_MUX_1>
>         <&tegra_pmx TEGRA_PMX_PG_DTD TEGRA_PMX_MUX_1>;

Assuming this is describing the pins a driver is using, how
about calling it pins?

That's because you might want to do all the muxing in a
bootloader, but still need to tell how many pins you're using
for MMC on a device. So it actually has a wider meaning than just
mux.

Also, we need to standardize on some name to use for parsing pins
using of_parse_phandle_with_args, and I suggested #pin-args.

>     config =
>         <&tegra_pmx TEGRA_PMX_PG_DTA TEGRA_PMX_CONF_TRISTATE 1>
>         <&tegra_pmx TEGRA_PMX_PG_DTD TEGRA_PMX_CONF_TRISTATE 1>
>         <&tegra_pmx TEGRA_PMX_PG_DTA TEGRA_PMX_CONF_DRIVE_STRENGTH 5>
>         <&tegra_pmx TEGRA_PMX_PG_DTD TEGRA_PMX_CONF_DRIVE_STRENGTH 5>
>         <&tegra_pmx TEGRA_PMX_PG_DTA TEGRA_PMX_CONF_SLEW_RATE 4>
>         <&tegra_pmx TEGRA_PMX_PG_DTD TEGRA_PMX_CONF_SLEW_RATE 8>;
> };

Here I don't quite understand how config is different from pins/mux
above? It seems to set the driver/pull stuff, but why don't you
just make #pin-args larger and have a wider pin array?

Something like:

	pins =
	<&tegra_pmx TEGRA_PMX_PG_DTA TEGRA_PMX_MUX_1 TEGRA_PMX_CONF_TRISTATE 1
	 &tegra_pmx TEGRA_PMX_PG_DTD TEGRA_PMX_MUX_1 TEGRA_PMX_CONF_TRISTATE 1>;

and in the parent set #pin-args to 3.
 
> (Note that I think we've agreed to remove the first cell above, &tegra_pmx,
> now by requiring such nodes exist as children of the pin controller.)

Sorry I don't quite follow, can you please maybe repost a complete
.dts entry for your pin controller and one driver entry?
 
> My assertion is that the common pinmux bindings define that the
> Interpretation of muxable_entity_id is left up to the binding of the
> specific pin controller. Hence, I can says "it's an integer, and here
> is the list of valid values and what they mean", and you can say "it's
> a phandle, which must refer to one of the per-pin nodes defined by the
> pin controller".
> 
> Does that work for you?

Yes it does, other than the comments above.

Regards,

Tony
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