Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752646AbbEKLur (ORCPT ); Mon, 11 May 2015 07:50:47 -0400 Received: from hqemgate16.nvidia.com ([216.228.121.65]:14781 "EHLO hqemgate16.nvidia.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751317AbbEKLuo (ORCPT ); Mon, 11 May 2015 07:50:44 -0400 X-PGP-Universal: processed; by hqnvupgp07.nvidia.com on Mon, 11 May 2015 04:49:05 -0700 Date: Mon, 11 May 2015 14:50:36 +0300 From: Peter De Schrijver To: Rhyland Klein CC: Mike Turquette , Stephen Warren , Stephen Boyd , Thierry Reding , Alexandre Courbot , , , , Bill Huang Subject: Re: [PATCH v2 16/19] clk: tegra: pll: Add Set_default logic Message-ID: <20150511115036.GG22637@tbergstrom-lnx.Nvidia.com> References: <1430328109-537-1-git-send-email-rklein@nvidia.com> <1430328109-537-17-git-send-email-rklein@nvidia.com> <20150430101225.GU3097@tbergstrom-lnx.Nvidia.com> <55424ACA.9010406@nvidia.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <55424ACA.9010406@nvidia.com> X-NVConfidentiality: public User-Agent: Mutt/1.5.21 (2010-09-15) X-Originating-IP: [10.21.24.170] X-ClientProxiedBy: UKMAIL101.nvidia.com (10.26.138.13) To UKMAIL101.nvidia.com (10.26.138.13) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2347 Lines: 50 On Thu, Apr 30, 2015 at 11:31:22AM -0400, Rhyland Klein wrote: > On 4/30/2015 6:12 AM, Peter De Schrijver wrote: > > On Wed, Apr 29, 2015 at 01:21:46PM -0400, Rhyland Klein wrote: > >> From: Bill Huang > >> > >> Add logic which (if specified for a pll) can verify that a PLL is set > >> to the proper default value and if not can set it. This can be > >> specified per PLL as each will have different default values. > >> > > > > Why can't we just set the default values at init time? > > Sorry, I did some investigation into this and wrote up a nice response > ... and forgot to hit send ... > > The reason this can't be run only once at init time is the following. In > reality, we want to have the defined default values written as early as > possible. Idealy, the bootloader could write these, so the kernel need > only check, see they are right, and not touch them. However, since we > can't rely on the bootloader to do so, the kernel needs the support to > be able to write these default values. At init time, some pll's will be > enabled (from bootloader) and because they are enabled (and the rest of > the clk framework isn't done being setup yet) we can't disable them to > write the full register values. Therefore, the set_defaults logic uses a > 2-pass system. > > first pass: Try to set defaults at init/registration time. If pll is > disabled, this works fine. If it is enabled, then we update a subset of > the register as a "best effort" setting of the defaults. > > second pass: Should only run the first time we go through set_rate for a > pll. If the first pass already wrote default value, then it skips this > step. Otherwise it will go in, once the pll is disabled in the set_rate > path, and write the full register default. > > This is required because some registers need to be reset to the default > values we have to ensure locking works correctly. Does that make sense? Ok. I see... Should we print a warning (pr_warn()) the bootloader isn't initializing the hw correctly if the second pass needs to write the default values? Thanks, Peter. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/