linux-kernel - Re: [RFC PATCH v2 4/4] mmc: sdhci-esdhc-imx: using pinmux subsystem

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Message-ID: <20111215090357.GA2267@S2100-06.ap.freescale.net>
Date:	Thu, 15 Dec 2011 17:03:58 +0800
From:	Shawn Guo <shawn.guo@...escale.com>
To:	Linus Walleij <linus.walleij@...aro.org>
CC:	Sascha Hauer <s.hauer@...gutronix.de>,
	Dong Aisheng <b29396@...escale.com>,
	<linus.walleij@...ricsson.com>, <linux-kernel@...r.kernel.org>,
	<rob.herring@...xeda.com>, <grant.likely@...retlab.ca>,
	<linux-arm-kernel@...ts.infradead.org>, <kernel@...gutronix.de>
Subject: Re: [RFC PATCH v2 4/4] mmc: sdhci-esdhc-imx: using pinmux subsystem

On Thu, Dec 15, 2011 at 09:26:40AM +0100, Linus Walleij wrote:
> On Thu, Dec 15, 2011 at 8:05 AM, Shawn Guo <shawn.guo@...escale.com> wrote:
> >[Me]
> >> So if you want to do this for i.MX you need something like
> >> selectable dummy pinmuxes, i.e. pinmux_get() to return something
> >> that just say "OK" to everything like the dummy regulators.
> >>
> >> Shall I try to create something like that?
> >>
> > Isn't the empty functions defined in include/linux/pinctrl/pinmux.h
> > for this purpose?
> 
> No, these are for compiling it *out*, dummy pinmuxes would
> be if you compile it *in*, but don't find an apropriate pinmux,
> you still get something that does nothing and still works.
> 
> Dummy regulators work exactly this way.
> 
> > It does not solve the problem with single image.
> 
> I think it does.
> 
> > You might probably mean that we create a dummy_pinctrl_desc and register
> > it to pinctrl core with pinctrl_register() if we detect that the kernel
> > is running on a soc that has no pinctrl support?
> 
> No. You have a #ifdef CONFIG_PINMUX_DUMMY in pinmux_get()
> that makes sure you return a working no-op pinmux handle even
> though there is no real pinmux behind it.
> 
Ah, ok.  So the problem will be sorted out at pinctrl core level, and
pinctrl driver will not be bothered at all.  Yes, please, we need this.

> > This is not a problem to pinctrl migration only.  We have the same
> > problem with common clk migration.  Unless we migrate imx3, imx5 and
> > imx6 to common clk at the same time, single image build just does not
> > cope with clk_* api.
> 
> And  you could have the same problem with regulator migration...
> Luckily dummy regulators saves you in that case.
> 
Not sure what will save me in common clk case though.

-- 
Regards,
Shawn

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