linux-kernel - Re: [PATCH] i2c: exynos5: Initialise Samsung High Speed I2C controller early

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Date:	Fri, 9 May 2014 14:51:53 +0100
From:	Mark Brown <broonie@...nel.org>
To:	Naveen Krishna Ch <naveenkrishna.ch@...il.com>
Cc:	Naveen Krishna Chatradhi <ch.naveen@...sung.com>,
	linux-i2c@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	"linux-samsung-soc@...r.kernel.org" 
	<linux-samsung-soc@...r.kernel.org>, sjg@...omium.org,
	grundler@...omium.org, linux-kernel@...r.kernel.org,
	wsa@...-dreams.de, cpgs@...sung.com
Subject: Re: [PATCH] i2c: exynos5: Initialise Samsung High Speed I2C
 controller early

On Fri, May 09, 2014 at 05:50:00PM +0530, Naveen Krishna Ch wrote:
> On 24 April 2014 21:55, Mark Brown <broonie@...nel.org> wrote:

> >> Such solution has been proposed by Mark Brown to fix the problem of
> >> the regulators not beeing available on the peripheral device probe():
> >> http://lists.infradead.org/pipermail/linux-arm-kernel/2010-March/011971.html

> > What specifically is this needed for?  We *should* be able to use
> > deferred probe for most things, but I know that not all subsystems are
> > able to yet.

> DRM related drivers like DP, FIMD, HDMI, Mixer wants to be probed ASAP
> during the boot.
> The real problem comes when, one of these drivers do a regulator_get().

> If the physical supply  is not enabled/hookedup the regulator_get() call
> assumes that physical supply is present and returns a
> "dummy_regulator" (But, not an error).

> Because of which, Display and several other devices fails to work.

These drivers are buggy, if they geniunely expect and handle a missing
supply then they should be using regulator_get_optional() to request the
regulator and even if they don't the use of subsys_initcall() is not
going to fix anything here - if a dummy regulator is going to be
returned the time things are probed won't make a difference.

> I2C, I2C_TUNNEL, SPI and DMA drivers are required as subsys_initcall()
> for similar reason.

What makes you say this?  Typically those drivers don't use regulators
at all.

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