[alsa-devel] [PATCH 1/3] ALSA: compress_core: Update calc_avail to use cumulative values

[Pierre-Louis Bossart]

On 4/5/13 3:36 AM, Charles Keepax wrote:
> On Thu, Apr 04, 2013 at 01:22:27PM -0500, Pierre-Louis Bossart wrote:
>> This isn't very elegant. In your implementation you bypass app_ptr and
>> hw_ptr to use cumulative values, for 'memory-mapped' DSPs we use app_ptr
>> and hw_ptr everywhere else. This patch seems to make things more
>> confused when they could be simpler without all these redundant fields?
>> I am probably partly responsible for the introduction of these
>> cumulative values, now I think the time has come to simplify things.
>
> I am not sure I agree this is less elegant it greatly simplifies
> the calculation of the available data for one, also half of the
> avail function was using them anyway. The cumulative values make
> less assumptions about the underlying representation (although
> admittedly it is rather unlikely this will be anything other than
> a ring buffer) and contain more information (ie. how much data
> has been transferred so far).
>
> You say we use app_ptr and hw_ptr everywhere else but only in
> places relating to situations where compress_offload is managing
> the buffer (ie. memory mapped DSPs). They feel more like internal
> buffer state, where the cumulative values surely reflect the
> stream state better.
>
> If anything if we were looking to simplify I would be inclined to
> keep the cumulative values?

That is my proposal as well, app_ptr and hw_ptr are defined as offsets 
but can't really be used to make the difference between buffer full and 
buffer empty and won't work for your implementation. I believe in the 
pcm case only cumulative values are used in the core.
Vinod, please chime in...
-Pierre