linux-kernel - [PATCH v3] ALSA: dmaengine_pcm: Consider DMA cache caused delay in pointer callback

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Date:   Mon, 10 Feb 2020 17:33:36 +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 v3] ALSA: 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>
Reviewed-by: Takashi Iwai <tiwai@...e.de>
---
Hi,

Changes since v2:
- align the substream->runtime users to use runtime.
- added Reviewed-by from Takashi-san

Changes since v1:
- use bytes_to_frames() for the DMA delay calculation
- Drop changes to soc-pcm

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 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/sound/core/pcm_dmaengine.c b/sound/core/pcm_dmaengine.c
index 5749a8a49784..9d4f48cfe47f 100644
--- a/sound/core/pcm_dmaengine.c
+++ b/sound/core/pcm_dmaengine.c
@@ -240,6 +240,7 @@ EXPORT_SYMBOL_GPL(snd_dmaengine_pcm_pointer_no_residue);
 snd_pcm_uframes_t snd_dmaengine_pcm_pointer(struct snd_pcm_substream *substream)
 {
 	struct dmaengine_pcm_runtime_data *prtd = substream_to_prtd(substream);
+	struct snd_pcm_runtime *runtime = substream->runtime;
 	struct dma_tx_state state;
 	enum dma_status status;
 	unsigned int buf_size;
@@ -250,9 +251,12 @@ snd_pcm_uframes_t snd_dmaengine_pcm_pointer(struct snd_pcm_substream *substream)
 		buf_size = snd_pcm_lib_buffer_bytes(substream);
 		if (state.residue > 0 && state.residue <= buf_size)
 			pos = buf_size - state.residue;
+
+		runtime->delay = bytes_to_frames(runtime,
+						 state.in_flight_bytes);
 	}
 
-	return bytes_to_frames(substream->runtime, pos);
+	return bytes_to_frames(runtime, pos);
 }
 EXPORT_SYMBOL_GPL(snd_dmaengine_pcm_pointer);
 
-- 
Peter

Texas Instruments Finland Oy, Porkkalankatu 22, 00180 Helsinki.
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