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

[Shawn Guo <shawn.guo@linaro.org>]

On Fri, Jan 13, 2012 at 10:16:36AM -0800, Stephen Warren wrote:
...
> For reference, that message is:
> 
> Linusw wrote:
> > On Mon, Dec 5, 2011 at 3:43 AM, Dong Aisheng <dongas86 <at> gmail.com> wrote:
> > > My current plan is to define all (might be frequently) used functoin
> > > and groups for the exist upstreamed board like 53 Loco and etc, is
> > > that ok?
> >
> > Yes, but do it in respective board file, so if we say, one day
> > stops to support a certain board we can just delete that board
> > file and be done with it.
> >
> > Plus this gives us a nice separation as we move toward
> > device trees. (I think.)
> 
> My interpretation of what Dong wrote there is "I'm only going to define
> the functions and groups that are actually in use by upstream boards,
> not everything the SoC supports". However, your (Shawn's) references to
> the email, it sounds like you're interpreting what Dong wrong as "I'm
> going to define some virtual groups that don't exist in HW but represent
> common use-cases of the HW".
> 
Then what does the word 'groups' in Dong's sentence means with your
understanding, considering there is no HW level pingroup on imx?

> Admittedly, the wording of Linusw's actually seems to agree more with how
> you're interpreting what Dong said, but in that case, I don't think his
> reply makes sense - the whole purpose of the mux mapping table is to
> represent the board-specific configuration. If we're going to circumvent
> it, we should completely remove it from the pinctrl subsystem, rather than
> having some boards avoid using it by creating virtual pin groups instead.
> 
IMO, it's a compromise.  It still makes sense to have concept of
pingroup in pinctrl subsystem, because platforms like Tegra have
the HW pingroup.

> > > > For imx6q example, we have 193 pins as the muxable entities, and for
> > > > each of those pin, there are 8 alternative functions.  Let's see what
> > > > we will have if we enumerate all the available functions for each pin.
> ...
> > > > We simply do not want to over bloat imx6q pinctrl driver with such
> > > > enumeration.
> > >
> > > Yes, I see you'd end up with a huge number of function definitions here.
> > >
> > > You may be able to avoid this by changing the way you name/number the
> > > functions though.
> > >
> > > The example above has a unique function name for every individual signal.
> > > instead, can you name functions based on the controller they connect to?
> > >
> > > So, instead of having:
> > >
> > > IMX6Q_PAD_SD2_DAT1__USDHC2_DAT1
> > > IMX6Q_PAD_SD2_DAT2__USDHC2_DAT2
> > > IMX6Q_PAD_SD2_DAT3__USDHC2_DAT3
> > > IMX6Q_PAD_SD2_DAT4__USDHC2_DAT4
> > >
> > > Can you replace this with a single:
> > >
> > > IMX_FUNC_USDHC2
> >
> > So all 'enum imx6q_pad_*' goes away, and instead, we define macros
> > IMX_FUNC_* at controller basis, correct?
> 
> Yes, something like that. The best set to choose probably differs based
> on the SoC and its mux capabilities. But thinking more, if you're going
> along this kind of route, I'd prefer to just define the "func0", "func1",
> ... "func7" functions that represent the raw HW selection instead.
> 
In this case, I do not see any point to define them, since it does not
make too much difference than integer 0, 1, ..., 7.

-- 
Regards,
Shawn