linux-kernel - Re: [PATCH 2/2] ARM: OMAP2+: Enable pinctrl dummy states

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Message-ID: <20120912010307.GP23092@atomide.com>
Date:	Tue, 11 Sep 2012 18:03:07 -0700
From:	Tony Lindgren <tony@...mide.com>
To:	Matt Porter <mporter@...com>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Grant Likely <grant.likely@...retlab.ca>,
	AnilKumar <anilkumar@...com>,
	Linux SPI Devel List 
	<spi-devel-general@...ts.sourceforge.net>,
	Linux OMAP List <linux-omap@...r.kernel.org>,
	Linux ARM Kernel List <linux-arm-kernel@...ts.infradead.org>,
	Linus Walleij <linus.walleij@...aro.org>
Subject: Re: [PATCH 2/2] ARM: OMAP2+: Enable pinctrl dummy states

* Matt Porter <mporter@...com> [120911 12:05]:
> On Tue, Sep 11, 2012 at 11:35:22AM -0700, Tony Lindgren wrote:
> > Added Linus Walleij to Cc as well.

Now I think I really managed to add Linus W to Cc, sent too fast
earlier.
...

> > But do you get an error then if the desired pins are not found?
> > If you do get an error, then sounds like it's OK to do.
>
> Hrm, no. In that case, it will be completely silent (assuming we took
> care of the pinmuxing in the bootloader) as it uses the dummy state.
> Only with debug on will you see the information that mcspi has used
> the dummy state as is the case with !DT.
...
 
> > Well I think we should consider at least the following:
> > 
> > 1. Always see warnings when device tree is populated with board-generic.
> >    If somebody wants to use bootloader only muxing with DT, they can patch
> >    in pinctrl_provide_dummies() somewhere. But let's assume we always
> >    want to see the warnings with board-generic.c and DT.
> 
> Ok, this is clear.
> 
> > 2. For legacy booting without DT, we should not see any warnings
> >    from pinctrl-single.c as it's DT based.
> 
> Right, except anything legacy booting without DT will require that
> dummy states be present otherwise it will fail probe.

But I guess we should enable the dummy states only for other
board-*.c files, not board-generic.c? 

> > 3. There may be other non-pinctrl drivers too that are not DT
> >    based, and in those cases we should see the warnings as well
> >    for in the non-DT case.
> 
> I'm not sure what you mean here. "non-pinctrl drivers" means any driver
> that is not yet pinctrl or DT enabled? It's unclear to me how this
> case has a bearing on mcspi and pinctrl enablement across legacy
> board-foo.c !DT booting platforms.

Right, sorry I meant "non DT pinctrl drivers"..
 
> However, I think if the approach was modified by only calling
> pinctrl_provide_dummies() when we are booting with DT populated
> and using board-generic.c then it will satisfy all of your
> concerns. Thoughts?

Hmm but shouldn't it be call pinctrl_provide_dummies() only
for other boards except board-generic.c? And that is assuming
we don't have any other "non DT pinctrl drivers" around.
 
> i.e. the legacy !DT booting will have dummy states and continue
> along through mcspi the way it does today, relying on board-foo level
> pinmux calls (or bootloader pinmuxing). Meanwhile DT booting will now
> require that a mcspi instance also require pinctrl entry in this dts.

Yes agreed, except let's just produce a warning for the pinctrl
errors..
 
> The only worrisome thing is the pinctrl requirement on DT booting is
> now an implicit requirement.

..as otherwise not much will work at this point :)
 
> > > > For board-generic.c we always want to see the warnings. And some boards
> > > > insist on doing all the muxing only in the bootloader.
> > > 
> > > Which warnings are you saying we should see in the board-generic.c
> > > case?  Sure, there's plenty of cases where this will be unused due to
> > > somebody setting all the muxes in the bootloader and then not using
> > > pinctrl data. I'll have to doublecheck but I believe that case is also
> > > fine as the -single driver can't override the dummy state if the DT has
> > > no pinctrl data for the spi driver.

I suggest all pinctrl errors should show up as warnings with
board-generic.c, but we should not exit out of the driver probe
on errors.

Regards,

Tony
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