Pinmux bindings proposal V2
Shawn Guo
shawn.guo at linaro.org
Fri Feb 3 03:46:04 EST 2012
On Thu, Feb 02, 2012 at 10:36:54AM -0800, Stephen Warren wrote:
> Shawn Guo wrote at Wednesday, February 01, 2012 7:36 AM:
> ...
> > I had a talk with Dong about this binding, and we think that it should
> > work well for imx if we have a couple of small pieces added.
> >
> > On Fri, Jan 20, 2012 at 02:22:20PM -0800, Stephen Warren wrote:
> > ...
> > > pmx_sdhci: pinconfig-sdhci {
> > > /*
> > > * The mux property is a list of muxable entities
> > > * and the mux function to select for it. The number
> > > * of cells in each entry is the pin controller's
> > > * #pinmux-cells property. The pin controller's
> > > * binding defines what the cells mean. The pinctrl
> > > * driver is responsible for mapping this data to
> > > * the (group, function) pair required to fill in
> > > * the pinctrl subsystem's pinmux mapping table.
> > > */
> > > mux =
> > > <TEGRA_PMX_PG_DTA TEGRA_PMX_MUX_SDIO1>
> > > <TEGRA_PMX_PG_DTD TEGRA_PMX_MUX_SDIO1>;
> >
> > We need a property like 'mux-unit' whose value can be either 'pin' or
> > 'pingroup' to reflect something you mentioned as muxable entity.
>
> I'm not sure I agree; see below.
>
> > The reason behind this is the DT logic inside pinctrl core needs to
> > know how the pinmux_map should be constructed from device tree.
>
> As a general statement, yes.
>
> > In tegra case, the 'mux-unit' is 'pingroup', the core should construct
> > pinmux_map entry for each row/element of 'mux'.
>
> Yes.
>
> > In imx case, the 'mux-unit' will be 'pin',
>
> OK.
>
> Just a note: Tegra30 also has per-pin muxability. Only Tegra20 muxes pins
> in groups. (although Tegra30 does some if its pin configuration in groups)
>
> > and we would expect core construct only
> > one pinmux_map entry there, with all the pins listed in 'mux' composing
> > the group that pinmux_map needs.
>
> This is where I disagree.
>
So what I read is you disagree how pinctrl core uses property 'mux-unit'
not the property itself.
> If the pinmux_map should only contain a single entry, wouldn't the DT
> mux property only contain a single entry?
>
So you are saying we should have a pinmux_map for each entry in the
mux property? I disagree with that. For imx usdhc example, we have
10 entries in mux property representing 10 pins and their mux values.
What we need is one pinmux_map rather than 10 for just one client
device.
> The reason being that if there's a single entry in the pinmux_map, the
> group name used in that entry must be a group that's supported directly
> by the pinctrl driver (that's just the way pinctrl works). As such, why
> not just write the device tree in terms of those groups?
>
> The only way I can see this not being true is if your pinctrl driver is
> also parsing these mux properties, and dynamically creating the groups
> that it exposes based on the list of pins in the mux property.
Yes, that's exactly what we are trying to do for imx.
> However,
> that seems like the wrong approach;
Where does it go wrong exactly?
> If you're dynamically defining groups
> in DT, I'd expect separate explicit driver-specific properties/nodes to
> define those groups, such that the pinctrl core's processing of the mux
> property to be identical in all cases.
>
It's not imx specific. It's generally useful for any soc that has pin
as the muxable entity. I think it should be the common part of this
binding and implemented in pinctrl core DT support.
--
Regards,
Shawn
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