linux-kernel - [PATCH] ASoC: dmaengine_pcm: Consider DMA cache caused delay in pointer callback

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Date:   Mon, 10 Feb 2020 16:04:23 +0200
From:   Peter Ujfalusi <peter.ujfalusi@...com>
To:     <broonie@...nel.org>, <lgirdwood@...il.com>, <tiwai@...e.com>,
        <perex@...ex.cz>
CC:     <lars@...afoo.de>, <alsa-devel@...a-project.org>,
        <vkoul@...nel.org>, <linux-kernel@...r.kernel.org>
Subject: [PATCH] ASoC: dmaengine_pcm: Consider DMA cache caused delay in pointer callback

Some DMA engines can have big FIFOs which adds to the latency.
The DMAengine framework can report the FIFO utilization in bytes. Use this
information for the delay reporting.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@...com>
---
Hi,

5.6-rc1 now have support for reporting the DMA cached data.
With this patch we can include it to the delay calculation.
The first DMA driver which reports this is the TI K3 UDMA driver.

Regards,
Peter

 sound/core/pcm_dmaengine.c | 6 ++++++
 sound/soc/soc-pcm.c        | 2 +-
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/sound/core/pcm_dmaengine.c b/sound/core/pcm_dmaengine.c
index 5749a8a49784..4f1395fd0160 100644
--- a/sound/core/pcm_dmaengine.c
+++ b/sound/core/pcm_dmaengine.c
@@ -247,9 +247,15 @@ snd_pcm_uframes_t snd_dmaengine_pcm_pointer(struct snd_pcm_substream *substream)
 
 	status = dmaengine_tx_status(prtd->dma_chan, prtd->cookie, &state);
 	if (status == DMA_IN_PROGRESS || status == DMA_PAUSED) {
+		struct snd_pcm_runtime *runtime = substream->runtime;
+		int sample_bits = snd_pcm_format_physical_width(runtime->format);
+
 		buf_size = snd_pcm_lib_buffer_bytes(substream);
 		if (state.residue > 0 && state.residue <= buf_size)
 			pos = buf_size - state.residue;
+
+		sample_bits *= runtime->channels;
+		runtime->delay = state.in_flight_bytes / (sample_bits / 8);
 	}
 
 	return bytes_to_frames(substream->runtime, pos);
diff --git a/sound/soc/soc-pcm.c b/sound/soc/soc-pcm.c
index ff1b7c7078e5..58ef508d70a3 100644
--- a/sound/soc/soc-pcm.c
+++ b/sound/soc/soc-pcm.c
@@ -1151,7 +1151,7 @@ static snd_pcm_uframes_t soc_pcm_pointer(struct snd_pcm_substream *substream)
 	}
 	delay += codec_delay;
 
-	runtime->delay = delay;
+	runtime->delay += delay;
 
 	return offset;
 }
-- 
Peter

Texas Instruments Finland Oy, Porkkalankatu 22, 00180 Helsinki.
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