[PATCH] ASoC: Intel: Unify HDAudio-ext bus initialization

[Pierre-Louis Bossart]

On 10/19/21 12:32 PM, Cezary Rojewski wrote:
> On 2021-10-19 6:58 PM, Pierre-Louis Bossart wrote:
>>>> hmm. It's not clear whether we should initialize the regular hdac_bus
>>>> fields in the ext_bus_init(). For plain HDA, these are also initialized
>>>> in the caller. E.g. in sound/pci/hda/hda_controller.c.
>>>>
>>>> So if we start cleaning up, should we go further put this in
>>>> snd_hdac_bus_init()?
>>>>
>>>> Then another is what is the right place for settings like "sync_write =
>>>> 1". While this settings applies to all current users of the extended
>>>> bus, this is really hw specific setting and not really a property of
>>>> the extended bus, so this feels a bit out-of-place.
>>>
>>> I'm rather in favor of bigger cleanups. We can definitely move further
>>> in the future : )
>>
>> I am not opposed to updates in this hdaudio-ext part, but I am in favor
>> of less ambitious step-by-step changes.
>>
>> a) This is legacy code where the initial authors have moved on, and it's
>> very hard to figure out what the intent was. It's quite common to have
>> discussion on feature v. bug, see e.g. the discussion we had on this in
>> https://github.com/thesofproject/linux/pull/3175#pullrequestreview-772674119
>>
>>
>> b) In addition, this code is shared between two teams with separate
>> testing/CI capabilities and limited number of commercial/shipping
>> devices. There is a very large risk of introducing bugs even with the
>> best intentions.
>>
>> Before we do any changes in functionality, there are already basic steps
>> that can be done, e.g. using consistent naming between variables, the
>> existing code is just confusing as can be:
>>
>> struct hdac_stream *stream;
>> struct hdac_ext_stream *stream;
>> struct hdac_stream *hstream;
>> struct hdac_ext_stream *hstream;
>>
>> I started basic cleanups here:
>> https://github.com/thesofproject/linux/pull/3158, I haven't had time to
>> complete this because of more important locking issues, but I intend to
>> send those clarifications for the next cycle.
>>
>> Again before we do large changes let's think of smaller steps and how we
>> are going to validate those changes.
> 
> Agree, step-by-step is the way to go.
> 
> Isn't this patch a 'step' though? This isn't remotely a refactor, just
> gathering of common parts of ext-bus initialization. We could start with
> this so legacy users are unaffected, then have snd_hdac_bus_init()
> updated so snd_hdac_ext_bus_init() is devoid of 'core' fields
> assignments as suggested by Kai.

If it was just moving common parts, I would have no issue. My main
objection is that you went one step further and started renaming stuff
in rather confusing ways, e.g.

-void sof_hda_bus_init(struct hdac_bus *bus, struct device *dev)
+void sof_hda_bus_init(struct hda_bus *bus, struct pci_dev *pdev,

- * snd_hdac_ext_bus_init - initialize a HD-audio extended bus
+ * snd_hda_ext_bus_init - initialize a HD-audio extended bus

hda_bus is a definition from hda_codec.h, I don't see a reason why we
should use this structure when the vast majority of the code uses
hdac_bus. And the purpose of hdac_ext is really to deal with
*controller* extensions to couple/decouple DMAs. There is no dependency
on codecs at that level.

Even if there was, I also don't really see why/when we should start
using hda_ext v. hdac_ext, the naming convention completely escapes me.
It would seem logical to me to only use hdac_ext as an extension of
hdac_, no?

I also don't get what this means:
+	snd_hda_ext_bus_init(hbus, pci, NULL, ext_ops, "sklbus");

what is 'sklbus' and what purpose are you trying to accomplish with this
change?