From mboxrd@z Thu Jan 1 00:00:00 1970 From: Naveen Krishna Ch Subject: Re: [PATCH] i2c: exynos5: Initialise Samsung High Speed I2C controller early Date: Fri, 9 May 2014 17:50:00 +0530 Message-ID: References: <1398350916-885-1-git-send-email-ch.naveen@samsung.com> <20140424162558.GB12304@sirena.org.uk> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Return-path: In-Reply-To: <20140424162558.GB12304-GFdadSzt00ze9xe1eoZjHA@public.gmane.org> Sender: linux-i2c-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Mark Brown Cc: Naveen Krishna Chatradhi , linux-i2c-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org, "linux-samsung-soc-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , sjg-F7+t8E8rja9g9hUCZPvPmw@public.gmane.org, grundler-F7+t8E8rja9g9hUCZPvPmw@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, wsa-z923LK4zBo2bacvFa/9K2g@public.gmane.org, cpgs-Sze3O3UU22JBDgjK7y7TUQ@public.gmane.org List-Id: linux-i2c@vger.kernel.org Hello Mark, On 24 April 2014 21:55, Mark Brown 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 :)