linux-kernel - Re: modalias char-major-10-130

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Message-ID: <20130705205307.GB14258@spo001.leaseweb.com>
Date:	Fri, 5 Jul 2013 22:53:07 +0200
From:	Wim Van Sebroeck <wim@...ana.be>
To:	Jean Delvare <jdelvare@...e.de>
Cc:	linux-watchdog@...r.kernel.org,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: modalias char-major-10-130

Hi Jean,

> All watchdog drivers include:
> 
> MODULE_ALIAS_MISCDEV(WATCHDOG_MINOR);
> 
> which causes a modalias char-major-10-130 to be added to every watchdog
> driver module. As a result, any access to /dev/watchdog on a system with
> no watchdog driver loaded and working will result in an attempt to load
> several dozen drivers. At best one or two will actually work, the others
> will:
> 
> * Waste time failing to load.
> * Waste memory succeeding to load but not finding any device to bind to.
> * Pollute the kernel log.
> * Sometimes even load while they should not and break the system. I just
> had a report about advantechwdt doing that on some systems.
> 
> And the attempt order will presumably be random, so it might as well
> load softdog before a hardware-based watchdog which would have been
> preferred.
> 
> This looks so 90s. Drivers for enumerated devices have hardware-based
> modaliases, so char-major-10-130 shouldn't be needed. Other drivers
> should certainly not be loaded randomly if they need to poke the
> hardware to detect the presence of a supported device.
> 
> My opinion is that the char-major-10-130 modalias should ONLY be defined
> by user-space, when the user knows he/she needs a watchdog driver which
> doesn't support auto-loading via hardware-based auto-loading.
> 
> So, can we please get rid of all these
> MODULE_ALIAS_MISCDEV(WATCHDOG_MINOR) statements? They do more harm than
> good as far as I can see.

You have a valid point: There were we have modaliases and other detection
mechanism we should indeed remove them. The rest should be evaluated
afterwards on a case by case basis. Certain intel based drivers should
(like advantechwdt) should indeed be fixed because they poke in the hardware
directly and can't be really detected.

Kind regards,
Wim.

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