linux-kernel - Re: [PATCH v2 00/16] Common Dell SMBIOS API

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Message-ID: <20160208192014.GN1779@malice.jf.intel.com>
Date:	Mon, 8 Feb 2016 11:20:14 -0800
From:	Darren Hart <dvhart@...radead.org>
To:	Pali Rohár <pali.rohar@...il.com>
Cc:	Michał Kępień <kernel@...pniu.pl>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Matthew Garrett <mjg59@...f.ucam.org>,
	Richard Purdie <rpurdie@...ys.net>,
	Jacek Anaszewski <j.anaszewski@...sung.com>,
	platform-driver-x86@...r.kernel.org, linux-leds@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 00/16] Common Dell SMBIOS API

On Fri, Jan 22, 2016 at 03:48:51PM +0100, Pali Rohár wrote:
> On Friday 22 January 2016 15:27:12 Michał Kępień wrote:
> > Note:
> > 
> >     In this series (both v1 and v2) I tried to stick to the overall
> >     concept used in dell-laptop, but in the v1 thread me and Pali also
> >     briefly discussed his alternative ideas [1][2] as to what this API
> >     could look like, so feel free to suggest a different approach.
> > 
> > [1] http://www.spinics.net/lists/platform-driver-x86/msg08260.html
> > [2] http://www.spinics.net/lists/platform-driver-x86/msg08268.html
> 
> I would like to hear opinion about dell-smbios API also from other
> people. Darren, can you look and comment it?

This is an excellently prepared series, nice work Michał.

Most of my concerns were addressed by later patches in the series. I have pushed
a version of this 1/7 fixed per lkp (linux/io.h) and 7/16 with a corrected body
as I sent in reply to that patch. This is on my tree as the dell-smbios branch.

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.

-- 
Darren Hart
Intel Open Source Technology Center