[alsa-devel] [PATCH 5/5] ALSA/i915: Check power well API existense before calling

Jaroslav Kysela perex at perex.cz
Mon May 13 10:55:46 CEST 2013

Date 13.5.2013 10:28, David Henningsson wrote:
> On 05/13/2013 09:37 AM, Wang Xingchao wrote:
>> I915 module maybe loaded after snd_hda_intel, the power-well
>> API doesnot exist in such case. This patch intended to avoid
>> loading dependency between snd-hda-intel and i915 module.
> Hi Xingchao and thanks for working on this.
> This patch seems to re-do some of the work done in other patches (a lot 
> of lines removed), so it's a little hard to follow. But I'll try to 
> write some overall comments on how I have envisioned things...
> 1. I don't think there's any need to create an additional kernel module, 
> we can just let hda_i915.c be in the snd-hda-intel.ko module, and only 
> compile it if DRM_I915 is defined.
> 2. We don't need an IS_HSW macro on the audio side. Instead declare a 
> new AZX_DCAPS_NEED_I915_POWER (or similar) driver quirk.
> 3. Somewhere in the beginning of the probing in hda_intel.c, we'll need 
> something like:
> if (driver_caps & AZX_DCAPS_NEED_I915_POWER)
>    hda_i915_init(chip);
> 4. The hda_i915_init does not need to be exported (they're now both in 
> the same module). hda_i915.h could have something like:
> #ifdef DRM_I915
>    void hda_i915_init(chip);
> #else
>    #define hda_i915_init(chip) do {} while(0)
> #endif
> 5. You're saying this patch is about avoid loading dependency between 
> snd-hda-intel and i915 module. That does not make sense to me, since the 
> powerwell API is in the i915 module, snd-hda-intel must load it when it 
> wants to enable power on haswell, right? Thus there is a loading 
> dependency. If the i915 module is not loaded at that point, we must wait 
> for it to load, so we can have proper power, instead of continuing 
> probing without the power well?

Looking to the code, if the drm code requires a callback to the audio
code, I would just register it in the audio driver init phase and
unregister it when snd-hda-intel is unloaded. This cross module loading
dependency looks really bad. Or it is not allowed to load the audio
driver later than DRM one?


Jaroslav Kysela <perex at perex.cz>
Linux Kernel Sound Maintainer
ALSA Project; Red Hat, Inc.

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