From mboxrd@z Thu Jan 1 00:00:00 1970 From: Arnd Bergmann Subject: Re: [PATCH] PM / OPP: Initialize regulator pointer to an error value Date: Tue, 16 Feb 2016 16:12:39 +0100 Message-ID: <10492578.n5ZTGbvbYE@wuerfel> References: <1455544758-7718-1-git-send-email-jonathanh@nvidia.com> <2628515.OmmYzoeulx@wuerfel> <20160216131108.GK18327@sirena.org.uk> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7Bit Return-path: Received: from mout.kundenserver.de ([212.227.17.10]:60967 "EHLO mout.kundenserver.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932640AbcBPPNC (ORCPT ); Tue, 16 Feb 2016 10:13:02 -0500 In-Reply-To: <20160216131108.GK18327@sirena.org.uk> Sender: linux-pm-owner@vger.kernel.org List-Id: linux-pm@vger.kernel.org To: linaro-kernel@lists.linaro.org Cc: Mark Brown , Nishanth Menon , linux-pm@vger.kernel.org, Viresh Kumar , Rafael Wysocki , linux-kernel@vger.kernel.org, Jon Hunter , Viresh Kumar , Stephen Boyd On Tuesday 16 February 2016 13:11:08 Mark Brown wrote: > On Tue, Feb 16, 2016 at 10:10:44AM +0100, Arnd Bergmann wrote: > > On Tuesday 16 February 2016 01:56:16 Mark Brown wrote: > > > > No, NULL is explicitly not something you can substitute in, > > > essentially all the users are just not bothering to implement error > > > checking and we don't want to encourage that. The set of use cases > > > where we legitimately have optional supplies is very small, much smaller > > > than clocks, because it makes the electrical engineering a lot harder. > > > I must have misinterpreted the idea behind that API as well then. > > > From this function definition: > > > static inline struct regulator *__must_check regulator_get(struct device *dev, > > const char *id) > > { > > /* Nothing except the stubbed out regulator API should be > > * looking at the value except to check if it is an error > > * value. Drivers are free to handle NULL specifically by > > * skipping all regulator API calls, but they don't have to. > > * Drivers which don't, should make sure they properly handle > > * corner cases of the API, such as regulator_get_voltage() > > * returning 0. > > */ > > return NULL; > > } > > This is the stubbed regulator API which is only ever used with the stub > regulator API, it uses NULL to give a non-error pointer it can return to > well written callers so they don't know they are running with the stubs. > We are explicitly using NULL because callers should treat it as a valid > regulator. Right, that is what I understood. > > my reading was that the expected behavior in any driver was: > > > * call regulator_get() > > * if IS_ERR(), fail device probe function, never use invalid > > pointer other than PTR_ERR() > > * if NULL, and regulator is required, fail probe so we never > > use the regulator > > No, drivers should never look at the value of the pointer other than to > check it for error. If there is a problem of any kind an error will be > returned. > > > * if NULL, and regulators are optional, continue with the NULL > > value. > > No, we always return an error pointer if we fail to get a regulator. > The difference with optional regulators is in how we handle the > situation where we have full constraints and a regulator is not mapped > in, normally we assume there must be one with no software control but we > need to work around buggy bindings as the device would be non-functional > without power. Sorry, I should not have said "optional" here, which has a specific meaning in the API. I meant a driver that can work with either CONFIG_REGULATOR enabled or disabled (which is something slightly different). I guess a driver needing to know whether regulators are built-in should check 'if (IS_ENABLED(CONFIG_REGULATOR))' rather than checking the return code for NULL. Arnd