Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752470AbbEKPHg (ORCPT ); Mon, 11 May 2015 11:07:36 -0400 Received: from hqemgate15.nvidia.com ([216.228.121.64]:7230 "EHLO hqemgate15.nvidia.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751045AbbEKPHe (ORCPT ); Mon, 11 May 2015 11:07:34 -0400 X-PGP-Universal: processed; by hqnvupgp07.nvidia.com on Mon, 11 May 2015 08:05:55 -0700 Message-ID: <5550C5B2.5030700@nvidia.com> Date: Mon, 11 May 2015 11:07:30 -0400 From: Rhyland Klein User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:31.0) Gecko/20100101 Thunderbird/31.6.0 MIME-Version: 1.0 To: Peter De Schrijver 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 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> <20150511115036.GG22637@tbergstrom-lnx.Nvidia.com> In-Reply-To: <20150511115036.GG22637@tbergstrom-lnx.Nvidia.com> Content-Type: text/plain; charset="windows-1252" Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3144 Lines: 75 On 5/11/2015 7:50 AM, Peter De Schrijver wrote: > 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? All the set default routines use the inline function "_pll_misc_chk_default" (used to be a MACRO). Inside, it compares register values vs expected defaults and warns: if (boot_val != default_val) { pr_warn("boot misc%d 0x%x: expected 0x%x\n", misc_num, boot_val, default_val); pr_warn(" (comparison mask = 0x%x)\n", mask); params->defaults_set = false; } so this is already done. I suppose the only other place we could add a warning is if the first past set-defaults can't be fully run since the clock is on, that might make things a little clearer, so I guess I'll go ahead and add that. -rhyland > > Thanks, > > Peter. > -- nvpublic -- 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/