Re: [PATCH] ALSA: hda - PCH HDA controller not controlled by i915 power

[Takashi Iwai <tiwai@suse.de>]

At Tue, 9 Jun 2015 08:43:44 +0000,
Yang, Libin wrote:
> 
> Hi Takashi,
> 
> > -----Original Message-----
> > From: Takashi Iwai [mailto:tiwai@suse.de]
> > Sent: Tuesday, June 09, 2015 4:30 PM
> > To: David Henningsson
> > Cc: Yang, Libin; alsa-devel@alsa-project.org
> > Subject: Re: [alsa-devel] [PATCH] ALSA: hda - PCH HDA controller not
> > controlled by i915 power
> > 
> > At Tue, 09 Jun 2015 08:46:35 +0200,
> > David Henningsson wrote:
> > >
> > >
> > >
> > > On 2015-06-09 08:31, Takashi Iwai wrote:
> > > > At Tue,  9 Jun 2015 14:05:18 +0800,
> > > > libin.yang@intel.com wrote:
> > > >>
> > > >> From: Libin Yang <libin.yang@intel.com>
> > > >>
> > > >> On some Intel platforms, the HDMI codec is connected to PCH
> > HDA
> > > >> controller. In this case, AZX_DCAPS_I915_POWERWELL is set and
> > > >> the i915 power well failure should not block the hda controller
> > > >> initialization.
> > > >>
> > > >> Signed-off-by: Libin Yang <libin.yang@intel.com>
> > > >
> > > > Is this fix needed for 4.1, or it's only for 4.2?
> > >
> > > It's a bug fix, and as such should go to all kernels, even with cc to
> > > stable. That said, it mainly concerns Skylake, so kernels that don't
> > > support Skylake would not need a backport.
> > 
> > The patch can't be applied even to 4.1 as is because of the code
> > structure change.  So, Cc to stable doesn't work, in anyway.
> > 
> > > > I vaguely remember of a bug report.  If there is any relevant bug
> > > > report, please give the link, too.
> > >
> > > I think this was raised to Intel by us. The use case is when the
> > > integrated GPU is disabled and a discrete GPU is used. In this case
> > the
> > > i915 module fails to load. If then the HDMI and analog codec are both
> > on
> > > the same controller, the entire controller fails instead of just the
> > > HDMI codec.
> 
> I can't find the bug number, maybe David can help.
> 
> BTW: Not only SKL but also other platforms that controller is not in 
> Powerwell while the controller connects with HDMI codec will meet
> such issue, like BSW.
> 
> > >
> > > I'll see if I can get the patch tested ASAP.
> > 
> > OK, the bug seems needed for 4.1 and earlier.  But Libin's patch is
> > only for 4.2.  And even worse, backporting this isn't
> > straightforward due to the lack of need_i915_power field.  Hmm.
> > 
> > I think we can make it easier by just allowing to continue the probe.
> > A totally untested patch for 4.1 is below.
> 
> Thanks for your help on this. So this patch will be merged or we will
> wait for 4.2 to merge the patch?

Let's see whether it works as expected.  
If this works for 4.1, we can merge back to 4.2 together with
additional NULL checks in hdac_i915.c.


Takashi