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

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Date:	Fri, 9 May 2014 17:50:00 +0530
From:	Naveen Krishna Ch <naveenkrishna.ch@...il.com>
To:	Mark Brown <broonie@...nel.org>
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

Hello Mark,

On 24 April 2014 21:55, Mark Brown <broonie@...nel.org> wrote:
> On Thu, Apr 24, 2014 at 08:18:36PM +0530, Naveen Krishna Chatradhi wrote:
>> This patch moves initialization code to subsys_initcall() to ensure
>> that the i2c bus is available early so the regulators can be quickly
>> probed and available for other devices on their probe() call.
>
>> 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.

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

-- 
Shine bright,
(: Nav :)
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