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

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Date:	Fri, 9 May 2014 15:54:25 +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 08:12:47PM +0530, Naveen Krishna Ch wrote:
> On 9 May 2014 19:21, Mark Brown <broonie@...nel.org> wrote:
> > On Fri, May 09, 2014 at 05:50:00PM +0530, Naveen Krishna Ch wrote:

> >> 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.

...

> If all the I2C, SPI, DMA, I2C_TUNNEL, DRM based LCD are all mod_probes()
> DRM drivers are probing a head of the PMIC probe. Which is causing the
> display drivers to get "dummy_regulators" instead of the real supplies.

No, it really won't - I have no idea what you are doing but it's not
mainline.  If you are getting dummy regulators then you don't have a
supply present at all and probe ordering isn't going to make a blind
bit of difference.

Please provide a specific technical description of the problem you are
seeing in mainline.

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