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

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Date:	Thu, 15 Dec 2011 14:23:36 +0100
From:	Sascha Hauer <s.hauer@...gutronix.de>
To:	Shawn Guo <shawn.guo@...escale.com>
Cc:	Dong Aisheng-B29396 <B29396@...escale.com>,
	Guo Shawn-R65073 <r65073@...escale.com>,
	Linus Walleij <linus.walleij@...aro.org>,
	"linus.walleij@...ricsson.com" <linus.walleij@...ricsson.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"rob.herring@...xeda.com" <rob.herring@...xeda.com>,
	"grant.likely@...retlab.ca" <grant.likely@...retlab.ca>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"kernel@...gutronix.de" <kernel@...gutronix.de>
Subject: Re: [RFC PATCH v2 4/4] mmc: sdhci-esdhc-imx: using pinmux subsystem

On Thu, Dec 15, 2011 at 08:17:54PM +0800, Shawn Guo wrote:
> On Thu, Dec 15, 2011 at 12:54:28PM +0100, Sascha Hauer wrote:
> > On Thu, Dec 15, 2011 at 07:53:05PM +0800, Shawn Guo wrote:
> > > On Thu, Dec 15, 2011 at 07:28:18PM +0800, Dong Aisheng-B29396 wrote:
> > > > > -----Original Message-----
> > > > > 
> > > > My understanding is that pinmux_get will return an error if no proper pinmux
> > > > Found without dummy pinmux. That's a real error.
> > > > But with dummy pinmux, if no proper pinmux found, the pinctrl core may check
> > > > If dummy pinmux is supported, if supported, it will fakely success with returning
> > > > a dummy pinmux. Then real error is hiden.
> > > > This is due to for supporting one single image, the dummy pinmux may also be enabled
> > > > For platforms like mx6q with real pinmux.
> > > > 
> > > Got your point.  So your concern is about the fake success when dummy
> > > pinmux comes to play rather than 'fake error'.  I'm not concerned about
> > > that case much, since we will know the failure with a simple debug/info
> > > message in the pinmux core, saying 'I do not find any available pinmux,
> > > and I'm falling into the dummy pinmux'.  When you see this message
> > > imx6q, you know something goes wrong.
> > 
> > So i.MX3/5 people must know that it's safe to ignore this message
> > whereas i.MX6 people must know there's something wrong Adding messages
> > saying "there might or might not be something wrong" is not good.
> > People will frequently ask on the mailing list about these messages.
> > 
> Usually, people checking the serial output and asking question on list
> are developers not users.  It's not too hard for developers to figure
> out such message.  Or we can making it a debug message, and when some
> driver is not working, turn on debug option, you know where it goes
> wrong.

So we as developers have to figure out ourselves what can go wrong and
the users, well who cares about users?

> 
> Anyway, it's not a problem to me.  I have seen similar messages on my
> kernel serial output.  I fail to see why pinmux can not do something
> that other subsystems are doing.

Yes, and everytime I see such a message I dig through the sourcecode
trying to find out if that's important or not. That's easy for me on
the systems I work with, but on my PC I am only a user, and honestly
on my PC I *want* to be only a user.

Sascha

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