Re: [RFC PATCH 0/2] ALSA: hda - acomp probe fix for i915

[Takashi Iwai <tiwai@suse.de>]

On Tue, 06 Oct 2020 13:30:40 +0200,
Kai Vehmanen wrote:
> 
> Hi,
> 
> this simple bugfix started to feel a bit like getting stuck in quicksand,
> so I'm looking for some early input via this RFC series.
> 
> Basicly hdac_i915.c should not use global state to track communication
> with i915 driver. But how to get handle of "hdac_bus*? I considered
> a few options:
> 
>   1) add hdac_bus as a member of drm_audio_component.h
> 	-> seems wrong as this is really an audio side implementation)
> 
>   2) embed copy of drm_audio_component to 'struct hdac_bus', so
>      I could use container_of() on the device handle to get
>      to the bus 
> 	-> wasted space to keep a copy at hdac_bus level
> 	   (note: snd-hda-codec-hdmi do this by embedding a copy
> 	    of ops to "struct hdmi_spec")
> 
>   3) add another devres entry to store the hdac_bus directly
>      in acomp_init and a new helper function to query it
> 
> I now implemented option 3 in this RFC series as it seemed cleanest
> and most local to hdac_component.c, where the problem stems from. It's still
> somewhat messy, and I'm wondering if I'm overlooking some obvious alternative.
> We could dig this deeper into i915 specific code, but OTOH, hdac_bus is
> an argument snd_hdac_acomp_init(), so it's common for all.
> 
> Kai Vehmanen (2):
>   ALSA: hda - keep track of HDA core bus instance in acomp
>   ALSA: hda/i915 - fix list corruption with concurrent probes

Another option would be to move the completion into the common acomp
helper from i915-specific one.  That is,

- Add bind_complete field into struct drm_audio_component,
  initialize it at snd_hdac_acomp_init()

- Call complete_all(&acomp->bind_complete) at the end of
  hdac_component_master_bind()

- Remove / replace i915's own completion with the hdac's one.
  The i915_init_ops can be dropped.


thanks,

Takashi