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

[Lin, Mengdong]

> -----Original Message-----
> From: Takashi Iwai [mailto:tiwai at suse.de]
> Sent: Wednesday, June 10, 2015 6:26 PM
> 
> Currently snd-hda-intel driver aborts the probing of Intel HD-audio controller
> with i915 power well management when binding with i915 driver via
> hda_i915_init() fails.  This is no big problem for Haswell and Broadwell where
> the HD-audio controllers are dedicated to HDMI/DP, thus i915 link is
> mandatory.  However, Skylake, Baytrail and Braswell have only one controller
> and both HDMI/DP and analog codecs share the same bus.  Thus, even if
> HDMI/DP isn't usable, we should keep the controller working for other codecs.
> 
> For fixing this, this patch simply allows continuing the probing even if
> hda_i915_init() call fails.  This may leave stale sound components for
> HDMI/DP devices that are unbound with graphics.  We could abort the
> probing selectively, but from the code simplicity POV, it's better to continue in
> all cases.
> 
> Reported-by: Libin Yang <libin.yang at intel.com>
> Signed-off-by: Takashi Iwai <tiwai at suse.de>
> ---
> This is for 4.1.  Appying to 4.2 may result in trivial conflicts.
> 
>  sound/pci/hda/hda_intel.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/sound/pci/hda/hda_intel.c b/sound/pci/hda/hda_intel.c index
> fea198c58196..8a0af6770e1d 100644
> --- a/sound/pci/hda/hda_intel.c
> +++ b/sound/pci/hda/hda_intel.c
> @@ -1855,7 +1855,7 @@ static int azx_probe_continue(struct azx *chip)
> #ifdef CONFIG_SND_HDA_I915
>  		err = hda_i915_init(hda);
>  		if (err < 0)
> -			goto out_free;
> +			goto skip_i915;
>  		err = hda_display_power(hda, true);
>  		if (err < 0) {
>  			dev_err(chip->card->dev,
> @@ -1865,6 +1865,7 @@ static int azx_probe_continue(struct azx *chip)
> #endif
>  	}
> 
> + skip_i915:
>  	err = azx_first_init(chip);
>  	if (err < 0)
>  		goto out_free;
> --
> 2.4.3

Thanks for your patch. But maybe we should not skip i915 for the dedicated
display HD-A controller on Haswell/Broadwell.

For HSW/BDW, their HD-A controller for display audio (PCI dev#3) is *partly*
in GPU power domain:
- Its PCI configuration space is out of i915 power well, but in an always-on
 power well. So even if the BIOS disables the Intel GPU (PCI dev#2), the HD-A
 controller is still present, and we can still access all standard registers in PCI
 config space. 

- Its audio functions are in the i915 power well. If hda_i915_init() fails and
 I915 power well is unavailable, read/write to the audio register of the
 Controller will fail and we'll get kernel error messages. So I feel it's better
 to abort if hda_i915_init() fails for this HD-A controller.

Thanks
Mengdong