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

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Message-ID: <CAA+hA=TrT=KSJGRyMeqW8u2BQ0xdW1o7hpJFENwRP7povc7ONg@mail.gmail.com>
Date:	Sun, 15 Jan 2012 02:21:19 +0800
From:	Dong Aisheng <dongas86@...il.com>
To:	Shawn Guo <shawn.guo@...aro.org>
Cc:	Stephen Warren <swarren@...dia.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>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"kernel@...gutronix.de" <kernel@...gutronix.de>,
	"cjb@...top.org" <cjb@...top.org>,
	"devicetree-discuss@...ts.ozlabs.org" 
	<devicetree-discuss@...ts.ozlabs.org>,
	"Simon Glass (sjg@...omium.org)" <sjg@...omium.org>,
	Richard Zhao <richard.zhao@...aro.org>
Subject: Re: [RFC PATCH v3 2/5] pinctrl: add dt binding support for pinmux mappings

On Sat, Jan 14, 2012 at 9:22 AM, Shawn Guo <shawn.guo@...aro.org> wrote:
> 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.
>
IMO can we the 'virtual' pin groups for IMX first in this very first step?
At least we found it works for IMX and easy to us and it's also
suitable for Tegra
, maybe others too. It also meets the design of current pinctrl subsystem.
And we can discuss and add individual pin support for dt later if really need,
that could avoid introducing much complexity for pinctrl dt support in
the first.

Beside although IMX does not group the pins together as a separate unit,
usually the pins are used in 'predefined' groups(from the meaning of pad name)
in most cases.
I think it's ok to think those pins a hw group:
like SD1_CMD, SD1_CLK, SD1_DAT0..SD1_DAT7 although those pins can also
be used as other function.

Regards
Dong Aisheng

>> > > > 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
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