linux-kernel - Re: crash on CONFIG_CFAG12864B=y in 2.6.20-rc3-mm1

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Message-Id: <1170352552.9781.212.camel@imap.mvista.com>
Date:	Thu, 01 Feb 2007 09:55:52 -0800
From:	Daniel Walker <dwalker@...sta.com>
To:	Miguel Ojeda <maxextreme@...il.com>
Cc:	akpm@...l.org, linux-kernel@...r.kernel.org
Subject: Re: crash on CONFIG_CFAG12864B=y in 2.6.20-rc3-mm1

On Thu, 2007-02-01 at 18:39 +0100, Miguel Ojeda wrote:
> On 2/1/07, Daniel Walker <dwalker@...sta.com> wrote:
> > On Thu, 2007-02-01 at 18:13 +0100, Miguel Ojeda wrote:
> >
> > > >
> > > >
> > >
> > > Well, I use the word "module" for both cases: When I modprobe
> > > cfag12864b, if ks0108 fails, it doesn't get linked. So I thought the
> > > same happen for built-in drivers (in other words, I didn't think
> > > cfag12864b would be linked if ks0108 failed).
> > >
> > > So I'm waiting until someone tell me what is the right way to avoid
> > > drivers like cfag12864b been inited if their dependencies failed.
> > >
> > > Anyway, thanks for discovering the bug (I wouldn't have discovered it
> > > as my motherboard has parallel port ;).
> >
> > I have a parallel port, but I don't have the cfag12864b or ks0108 .. I
> 
> In fact, you don't need the cfag12864b display, as the driver just
> needs the parallel port for output (you can put some LEDs attached to
> the parallel port to check the driver's operations and it will be
> fine).
> 
> BTW, why ks0108 didn't find the 888 parallel port? Haven't you got such number?

You know I think your right, it may not have a parallel port.. It's so
common I tend to take it for granted .

> > think the simplest way to fix it would be to add a flag to ks0108 that
> > signals successful initialization , then force cfag12864b to check for
> > that ..
> 
> Sure, that won't be a problem; however, maybe there is other better way (?).

When you build the driver as a module the module loader will only load
what is needed, and in order .. When the same driver is built-in the
module_init() becomes a device_initcall() , and all device_initcall's
get executed .. So you have to expect that cfag12864b drivers initcalls
will run eventually and will need to be careful about it's
initialization.

Daniel

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