From mboxrd@z Thu Jan 1 00:00:00 1970 From: Lukas Wunner Subject: Re: [PATCH v2 00/16] Common Dell SMBIOS API Date: Mon, 8 Feb 2016 20:30:07 +0100 Message-ID: <20160208193007.GA14985@wunner.de> References: <1453472848-3118-1-git-send-email-kernel@kempniu.pl> <20160122144851.GN7192@pali> <20160208192014.GN1779@malice.jf.intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20160208192014.GN1779@malice.jf.intel.com> Sender: platform-driver-x86-owner@vger.kernel.org To: Darren Hart Cc: Pali =?iso-8859-1?Q?Roh=E1r?= , Micha?? K??pie?? , Greg Kroah-Hartman , Matthew Garrett , Richard Purdie , Jacek Anaszewski , platform-driver-x86@vger.kernel.org, linux-leds@vger.kernel.org, linux-kernel@vger.kernel.org List-Id: linux-leds@vger.kernel.org Hi, On Mon, Feb 08, 2016 at 11:20:14AM -0800, Darren Hart wrote: > My only major concern is module load order dependencies. Inter-module > dependencies are frowned upon with good reason, the kernel load ordering is > non-deterministic and it's possible, for example, for dell-laptop to fail to > find the symbols exported by dell-smbios under certain conditions. > > I have worked around this in the past with things like the following: > > #ifdef MODULE > #ifdef CONFIG_FOO_MODULE > if (request_module("foo")) > return -ENODEV; > #endif > #endif > > Something like the above may be necessary for dell-smbios in dell-laptop, > dell-wmi, and dell-leds now that they depend on the dell-smbios exported > functions. > > Cc Greg in case there is a better way to handle this that I'm not aware of. Deferred probing seems to be the preferred way, see e.g.: https://lists.freedesktop.org/archives/dri-devel/2016-January/098404.html (In this example, apple_gmux_present() determines presence of the device and !vga_switcheroo_handler_flags() determine non-presence of its driver.) This will also work if the subsystem depended on is compiled in rather than in a module. Best regards, Lukas