linux-kernel - Re: [RFC PATCH v3 2/5] pinctrl: add dt binding support for pinmux mappings

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Date:	Fri, 6 Jan 2012 14:21:39 +0800
From:	Shawn Guo <shawn.guo@...aro.org>
To:	Stephen Warren <swarren@...dia.com>
Cc:	Shawn Guo <shawn.guo@...escale.com>,
	Dong Aisheng-B29396 <B29396@...escale.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"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>,
	"devicetree-discuss@...ts.ozlabs.org" 
	<devicetree-discuss@...ts.ozlabs.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [RFC PATCH v3 2/5] pinctrl: add dt binding support for pinmux
 mappings

On Thu, Jan 05, 2012 at 03:45:56PM -0800, Stephen Warren wrote:
> Shawn Guo wrote at Wednesday, December 28, 2011 7:47 PM:
> > On Tue, Dec 27, 2011 at 02:41:25PM +0000, Dong Aisheng-B29396 wrote:
> ...
> > > I was ever thought putting a phandle of pinmux function in each device,
> > > Then pinmux mapping table seems not need anymore. Like:
> > >
> > > usdhc4: usdhc@...9c000 { /* uSDHC4 */
> > >         compatible = "fsl,imx6q-usdhc";
> > > 	....
> > >         pinmux = <&pinmux-sd4>;
> > > };
> > >
> > > iomuxc@...e0000 {
> > >         pinmux-sd4 : sd4 {
> > >                 func-name = "sd4";
> > >                 grp-name = "sd4grp";
> > >                 grp-pins = <170 171 180 181 182 183 184 185 186 187>;
> > >                 num-pins = <10>;
> > >                 grp-mux = <0 0 1 1 1 1 1 1 1 1>;
> > >                 num-mux = <10>;
> > >         };
> > >
> > > It is a pure hw point of view to define node.
> > 
> > That's the way we should go for.  This is exactly the same thing that
> > clk and regulator DT support is doing.  And right, in that way, we do
> > not need pinmux mapping for DT at all.
> 
> Well, we'd probably want to have at least a semi-standardized notion of
> how the per-device "pinmux" property worked, much like interrupts and
> GPIOs work in the same way everywhere, albeit perhaps with different
> property names (for GPIOs) and controller-specific flags arguments etc.
> 
Agreed.

> One other thing to note: The per-device data can't be a single phandle
> reference, unless the referenced node is some kind of table,

Just like gpio and clock, it could reasonably be a phandle array
instead of a single phandle for some cases.

> and then
> we do need a pinmux mapping for DT to define the format of that table.
> Reasons being:
> 
> * Devices most likely need to configure more than one pin or group of
> pins, and may need to configure them to different functions, so we at
> least need an array of (pin_group, selected_function) values somewhere.
> 
> * We need to represent both mux function selection and arbitrary other
> per-pin/group configuration parameters.
> 
> * We need to represent pinmux configuration for multiple device/driver
> states; suspend, active, idle, ...?
> 
> ...
> > To make the pinmux api generic for both dt and non-dt users, the pinmux
> > client driver should still see/call pinmux_get, something like
> > of_pinmux_get should be sorted out behind pinmux_get.
> > 
> > > But what about the pin maps without device associated?
> >
> > Do we have such cases?
> 
> I think so.
> 
> At least early on, not all drivers will be pinmux-aware, and we'll still
> need to set up the pinmux for them. A system wide "pinmux initial
> configuration table" or similar would be needed to do this, I think.
> This may be transitional.

Ok.  But on imx, we usually have those early pinmux setting done in
bootloader.

Regards,
Shawn

> 
> I can easily see cases where we don't have an explicit driver for HW,
> but still need to set up random pinmux configuration as part of basic
> system initialization. Perhaps ideally we'd always tie pinmux usage to
> some specific device, but the flexibility of not having to do so seems
> useful.
> 
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