[Intel-gfx] [PATCH] drm/i915: add audio_ptr pointer check

[Takashi Iwai]

On Wed, 02 Mar 2016 08:59:23 +0100,
Yang, Libin wrote:
> 
> Hi Takashi,
> 
> > -----Original Message-----
> > From: Takashi Iwai [mailto:tiwai at suse.de]
> > Sent: Wednesday, March 02, 2016 3:44 PM
> > To: libin.yang at linux.intel.com
> > Cc: intel-gfx at lists.freedesktop.org; conselvan2 at gmail.com;
> > jani.nikula at linux.intel.com; ville.syrjala at linux.intel.com; Vetter, Daniel;
> > tiwai at suse.de; Yang, Libin
> > Subject: Re: [PATCH] drm/i915: add audio_ptr pointer check
> > 
> > On Wed, 02 Mar 2016 03:24:31 +0100,
> > libin.yang at linux.intel.com wrote:
> > >
> > > From: Libin Yang <libin.yang at linux.intel.com>
> > >
> > > check to make sure audio_ptr is not NULL before
> > > using it.
> > 
> > I don't think non-NULL is mandatory.  If any invalid access is seen,
> > it should be fixed rather in the audio side.
> 
> When I enable MST with other patches (not submitted so far),
> I found system may be random hang when boot up.
> 
> After apply this patch and another patch (I sent the patch in
> ALSA Mail list: ALSA: hda - hdmi defer to register acomp eld notifier),
> the hang issue is fixed.
> 
> I make the patch because in sound driver side, setting audio_ptr and
> audio_ops is not in the lock. I'm wondering that the compiler or CPU
> may optimize and change the setting order (the gfx code and alsa code
> may run parallelly?).

There are several ways to deal with such a thing.  An easy one would
be the memory barrier.


Takashi