[alsa-devel] [PATCH 2/7] ALSA: core: add .update_appl_ptr callback for pcm ops

[Pierre-Louis Bossart]

>>>> When appl_ptr is updated let low-level driver know, e.g.  to let the
>>>> low-level driver/hardware pre-fetch data opportunistically.
>>>>
>>>> The existing .ack callback could be used but it would need to be
>>>> extended with new arguments, resulting in multiple changes in legacy
>>>> code.
>>>
>>> I wouldn't mind changing these callers.  They aren't so many, after
>>> all.
>>
>> Yes this was one of the discussions we had in the past. I don't recall the
>> conclusion so had recommened to keep as is and discuss here.
>>
>> Do you think it's better to do that or use a new one :)
>
> It's OK to change ack callback, and actually it'll be cleaner.
> But then it'll be a problem in the next patch, I suppose :)

The main problem is test/coverage of legacy v. alignment of 
functionality. If we change .ack() then others will have to test for the 
changes and there's a risk of a regression on a specific platform that 
wasn't tested - Murphy's law applies.