Re: [PATCH 1/2] ALSA: hda - Continue probing even if i915 binding fails

[Takashi Iwai <tiwai@suse.de>]

At Fri, 12 Jun 2015 16:33:32 +0200,
David Henningsson wrote:
> 
> 
> 
> On 2015-06-12 16:14, Takashi Iwai wrote:
> > At Fri, 12 Jun 2015 08:37:38 +0200,
> > Takashi Iwai wrote:
> >>
> >> At Fri, 12 Jun 2015 08:17:12 +0200,
> >> David Henningsson wrote:
> >>> If BIOS disables the power well, then we would get the "audio register
> >>> I/O error" in the boot phase, there will be no codecs detected, and thus
> >>> no broken sound card showing up.
> >>>
> >>> The only issue is if the i915 driver disables the power well, but the
> >>> case that the i915 should be functioning enough to turn off the power
> >>> well at some point, and at the same time so broken that we can't bind to
> >>> it, seems extremely unlikely to me.
> >>>
> >>> Either the i915 driver works, or it does not. In both cases, continuing
> >>> probing is the more useful option.
> >>
> >> I don't see much usefulness there but rather simplicity.
> >>
> >> The binding with i915 won't happen at the later stage, thus the device
> >> is just a placeholder.  Any other goodies by keeping the dead device?
> >>
> >>>> Fair enough.  Then I'm going to queue the patch below in addition to
> >>>> for-linus branch.
> >>>
> >>> We'll have to agree to disagree on that, then.
> >>
> >> One point that hasn't been mentioned is the behavior change from the
> >> previous kernels.  The previous kernels abort probing, and it was OK
> >> since we supposed only HSW/BDW before 4.1.  Now, with continuing the
> >> probe, user sees the new device that hasn't been there, and yet the
> >> device is dead and merely a placeholder.
> >
> > Is this convincing enough for you?  Or would you still like to make
> > the broken HDMI/DP device enabled for HSW/BDW?
> 
> I guess the question is whether HDMI/DP can actually work without the 
> i915 driver, e g when running with nomodeset. If there is absolutely no 
> possibility whatsoever (e g maybe BIOS could set up the device so that 
> it works?), then it does not matter much, I suppose.

It can't work because we don't get proper ELD thus cannot setup
HDMI/DP CA bits.


Takashi