tree eb9b2cb7278d2e8bd441ec376226ebaa0325cd3b
parent fb418fe26d28378700bddc16f5fa3362dda86d1b
author Christophe Leroy <christophe.leroy@csgroup.eu> 1758209650 +0200
committer Mark Brown <broonie@kernel.org> 1758232247 +0100
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ASoC: fsl: fsl_qmc_audio: Only request completion on last channel

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.

Acked-by: Herve Codina <herve.codina@bootlin.com>
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Link: https://patch.msgid.link/bbd5167d190bbb45c3a4cd6ef2dece8817e0cc1e.1758209158.git.christophe.leroy@csgroup.eu
Signed-off-by: Mark Brown <broonie@kernel.org>