From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753371AbaEIMUW (ORCPT ); Fri, 9 May 2014 08:20:22 -0400 Received: from mail-ob0-f182.google.com ([209.85.214.182]:64181 "EHLO mail-ob0-f182.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750702AbaEIMUV (ORCPT ); Fri, 9 May 2014 08:20:21 -0400 MIME-Version: 1.0 In-Reply-To: <20140424162558.GB12304@sirena.org.uk> References: <1398350916-885-1-git-send-email-ch.naveen@samsung.com> <20140424162558.GB12304@sirena.org.uk> From: Naveen Krishna Ch Date: Fri, 9 May 2014 17:50:00 +0530 Message-ID: Subject: Re: [PATCH] i2c: exynos5: Initialise Samsung High Speed I2C controller early To: Mark Brown Cc: Naveen Krishna Chatradhi , linux-i2c@vger.kernel.org, linux-arm-kernel@lists.infradead.org, "linux-samsung-soc@vger.kernel.org" , sjg@chromium.org, grundler@chromium.org, linux-kernel@vger.kernel.org, wsa@the-dreams.de, cpgs@samsung.com Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@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 :)