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 188d9ca ("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>

Author: chleroy

sound/soc/fsl/fsl_qmc_audio.c

@@ -57,7 +57,6 @@ struct qmc_dai_prtd {
 	size_t ch_dma_offset;
 
 	unsigned int channels;
-	DECLARE_BITMAP(chans_pending, 64);
 	struct snd_pcm_substream *substream;
 };
 
@@ -126,17 +125,14 @@ static int qmc_audio_pcm_write_submit(struct qmc_dai_prtd *prtd)
 	int ret;
 
 	for (i = 0; i < prtd->channels; i++) {
-		bitmap_set(prtd->chans_pending, i, 1);
-
 		ret = qmc_chan_write_submit(prtd->qmc_dai->chans[i].qmc_chan,
 					    prtd->ch_dma_addr_current + i * prtd->ch_dma_offset,
 					    prtd->ch_dma_size,
-					    qmc_audio_pcm_write_complete,
-					    &prtd->qmc_dai->chans[i]);
+					    i == prtd->channels - 1 ? qmc_audio_pcm_write_complete :
+								      NULL, prtd);
 		if (ret) {
 			dev_err(prtd->qmc_dai->dev, "write_submit %u failed %d\n",
 				i, ret);
-			bitmap_clear(prtd->chans_pending, i, 1);
 			return ret;
 		}
 	}
@@ -146,20 +142,7 @@ static int qmc_audio_pcm_write_submit(struct qmc_dai_prtd *prtd)
 
 static void qmc_audio_pcm_write_complete(void *context)
 {
-	struct qmc_dai_chan *chan = context;
-	struct qmc_dai_prtd *prtd;
-
-	prtd = chan->prtd_tx;
-
-	/* Mark the current channel as completed */
-	bitmap_clear(prtd->chans_pending, chan - prtd->qmc_dai->chans, 1);
-
-	/*
-	 * All QMC channels involved must have completed their transfer before
-	 * submitting a new one.
-	 */
-	if (!bitmap_empty(prtd->chans_pending, 64))
-		return;
+	struct qmc_dai_prtd *prtd = context;
 
 	prtd->buffer_ended += prtd->period_size;
 	if (prtd->buffer_ended >= prtd->buffer_size)
@@ -182,17 +165,14 @@ static int qmc_audio_pcm_read_submit(struct qmc_dai_prtd *prtd)
 	int ret;
 
 	for (i = 0; i < prtd->channels; i++) {
-		bitmap_set(prtd->chans_pending, i, 1);
-
 		ret = qmc_chan_read_submit(prtd->qmc_dai->chans[i].qmc_chan,
 					   prtd->ch_dma_addr_current + i * prtd->ch_dma_offset,
 					   prtd->ch_dma_size,
-					   qmc_audio_pcm_read_complete,
-					   &prtd->qmc_dai->chans[i]);
+					   i == prtd->channels - 1 ? qmc_audio_pcm_read_complete :
+								     NULL, prtd);
 		if (ret) {
 			dev_err(prtd->qmc_dai->dev, "read_submit %u failed %d\n",
 				i, ret);
-			bitmap_clear(prtd->chans_pending, i, 1);
 			return ret;
 		}
 	}
@@ -202,26 +182,13 @@ static int qmc_audio_pcm_read_submit(struct qmc_dai_prtd *prtd)
 
 static void qmc_audio_pcm_read_complete(void *context, size_t length, unsigned int flags)
 {
-	struct qmc_dai_chan *chan = context;
-	struct qmc_dai_prtd *prtd;
-
-	prtd = chan->prtd_rx;
-
-	/* Mark the current channel as completed */
-	bitmap_clear(prtd->chans_pending, chan - prtd->qmc_dai->chans, 1);
+	struct qmc_dai_prtd *prtd = context;
 
 	if (length != prtd->ch_dma_size) {
 		dev_err(prtd->qmc_dai->dev, "read complete length = %zu, exp %zu\n",
 			length, prtd->ch_dma_size);
 	}
 
-	/*
-	 * All QMC channels involved must have completed their transfer before
-	 * submitting a new one.
-	 */
-	if (!bitmap_empty(prtd->chans_pending, 64))
-		return;
-
 	prtd->buffer_ended += prtd->period_size;
 	if (prtd->buffer_ended >= prtd->buffer_size)
 		prtd->buffer_ended = 0;
@@ -249,7 +216,6 @@ static int qmc_audio_pcm_trigger(struct snd_soc_component *component,
 
 	switch (cmd) {
 	case SNDRV_PCM_TRIGGER_START:
-		bitmap_zero(prtd->chans_pending, 64);
 		prtd->buffer_ended = 0;
 		prtd->ch_dma_addr_current = prtd->ch_dma_addr_start;