[PATCH v2 0/4] ASoC: fsl: fsl_qmc_audio: Reduce amount of interrupts

[Christophe Leroy <christophe.leroy@csgroup.eu>]

This series reduces significantly the amount of interrupts on
fsl_qmc_audio device.

Patches 1 and 2 are preparatory patches.
Patch 3 is the main change
Patch 4 is a cleanup which is enabled by previous patch

Changes in v2:
- Don't remove UB bit (Patch 1, comment from Herve Codina)
- Make sure audio channels are ordered on TDM bus (Patch 2, new patch, comment from Herve Codina)
- Drop struct qmc_dai_chan  (patch 4, new patch)

Backgroup (copied from patch 3):

In non-interleaved mode, several QMC channels are used in sync.
More details can be found in commit 188d9cae5438 ("ASoC: fsl:
fsl_qmc_audio: Add support for non-interleaved mode.")
At the time being, an interrupt is requested on each channel to
perform capture/playback completion, allthough the completion is
really performed only once all channels have completed their work.

This leads to a lot more interrupts than really needed. Looking at
/proc/interrupts shows ~3800 interrupts per second when using
4 capture and 4 playback devices with 5ms periods while
only 1600 (200 x 4 + 200 x 4) periods are processed during one second.

The QMC channels work in sync, the one started first is the one
finishing first and the one started last is the one finishing last,
so when the last one finishes it is guaranteed that the other ones are
finished as well. Therefore only request completion processing on the
last QMC channel.

On my board with the above exemple, on a kernel started with
'threadirqs' option, the QMC irq thread uses 16% CPU time with this
patch while it uses 26% CPU time without this patch.

Christophe Leroy (4):
  soc: fsl: qmc: Only set completion interrupt when needed
  ASoc: fsl: fsl_qmc_audio: Ensure audio channels are ordered in TDM bus
  ASoC: fsl: fsl_qmc_audio: Only request completion on last channel
  ASoc: fsl: fsl_qmc_audio: Drop struct qmc_dai_chan

 drivers/soc/fsl/qe/qmc.c      |  44 +++++++++---
 sound/soc/fsl/fsl_qmc_audio.c | 125 +++++++++++++++-------------------
 2 files changed, 87 insertions(+), 82 deletions(-)

-- 
2.49.0