snd_hdspe(4): Only buffer_copy() audio data once.

[dev_submerge.ch]

Summary

Instead of blindly copying two periods of audio data to and from DMA
buffers, keep track of the writing position and derive the actual
part of audio data that needs to be copied.
This approximately halves the number of samples copied in total.

[dev_submerge.ch]

I'm still testing this, but I haven't found any problems in the last few days. It's hard to tell whether this approach is robust against missed interrupts, because I never encountered any.

Ruslan, does the calculation of position and length look reasonable to you? We have to store the playback writing position extra because we don't set it in the sndbuf structure.

[br]

In D44084#1005680, @dev_submerge.ch wrote:

I'm still testing this, but I haven't found any problems in the last few days. It's hard to tell whether this approach is robust against missed interrupts, because I never encountered any.

Ruslan, does the calculation of position and length look reasonable to you? We have to store the playback writing position extra because we don't set it in the sndbuf structure.

looks ok to me, I have been testing this for about a week -- no issues

[dev_submerge.ch]

In D44084#1010276, @br wrote:

In D44084#1005680, @dev_submerge.ch wrote:

I'm still testing this, but I haven't found any problems in the last few days. It's hard to tell whether this approach is robust against missed interrupts, because I never encountered any.

Ruslan, does the calculation of position and length look reasonable to you? We have to store the playback writing position extra because we don't set it in the sndbuf structure.

looks ok to me, I have been testing this for about a week -- no issues

Did some more testing, no problems so far - I think you can commit this, thanks again!