Re: [PATCH] platform/x86: fujitsu-laptop: Don't oops when FUJ02E3 is not presnt

[Jonathan Woithe <jwoithe@just42.net>]

On Mon, Sep 25, 2017 at 03:14:41PM +0300, Ville Syrjälä wrote:
> On Sat, Sep 23, 2017 at 06:38:40PM +0930, Jonathan Woithe wrote:
> > > I'm curious by what you mean with "it even seems to work". Since it
> > > crashes when adjusting, what does it do that "works" ?
> > 
> > As mentioned earlier, I have assumed that this means the backlight
> > adjustment works correctly if the suggested patch has been applied.
> 
> Yes.

Great - thanks for confirming.

> > Having
> > thought about this some more I am unconvinced: if fext is NULL then
> > call_fext_func() (with the check added) can't have any effect.  The
> > backlight adjustment might still work, but it's not due to this code path.
> 
> It still calls set_lcd_level() which I assume is the thing that makes it
> work.

Yes, of course.  Thanks, I was overthinking things. :-)

Darren: this confirms that the idea of only registering FUJ02B1 if FUJ02E3
exists is no good: the S6120 (and probably others) needs FUJ02B1 but doesn't
have a FUJ02E3.  This means that at least for the purposes of addressing
this regression, the null device check is the best option: either in
bl_update_status() (Ville's original patch) or in call_fext_func() (as
suggested by Michel, with a suggested patch in my post on the 24th).

Regards
  jonathan