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

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

[Peter Ujfalusi]

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@ti.com>
Reviewed-by: Takashi Iwai <tiwai@suse.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.
Y-tunnus/Business ID: 0615521-4. Kotipaikka/Domicile: Helsinki

Applied "ALSA: dmaengine_pcm: Consider DMA cache caused delay in pointer callback" to the asoc tree

[Mark Brown]

The patch

   ALSA: dmaengine_pcm: Consider DMA cache caused delay in pointer callback

has been applied to the asoc tree at

   https://git.kernel.org/pub/scm/linux/kernel/git/broonie/sound.git for-5.7

All being well this means that it will be integrated into the linux-next
tree (usually sometime in the next 24 hours) and sent to Linus during
the next merge window (or sooner if it is a bug fix), however if
problems are discovered then the patch may be dropped or reverted.  

You may get further e-mails resulting from automated or manual testing
and review of the tree, please engage with people reporting problems and
send followup patches addressing any issues that are reported if needed.

If any updates are required or you are submitting further changes they
should be sent as incremental updates against current git, existing
patches will not be replaced.

Please add any relevant lists and maintainers to the CCs when replying
to this mail.

Thanks,
Mark

From 9d789dc047e32fb0f85ff192f883a534017512a2 Mon Sep 17 00:00:00 2001
From: Peter Ujfalusi <peter.ujfalusi@ti.com>
Date: Mon, 10 Feb 2020 17:33:36 +0200
Subject: [PATCH] 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@ti.com>
Reviewed-by: Takashi Iwai <tiwai@suse.de>
Link: https://lore.kernel.org/r/20200210153336.10218-1-peter.ujfalusi@ti.com
Signed-off-by: Mark Brown <broonie@kernel.org>
---
 sound/core/pcm_dmaengine.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/sound/core/pcm_dmaengine.c b/sound/core/pcm_dmaengine.c
index d8be7b488162..6852bb670b4e 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;
@@ -257,7 +258,7 @@ snd_pcm_uframes_t snd_dmaengine_pcm_pointer(struct snd_pcm_substream *substream)
 						 state.in_flight_bytes);
 	}
 
-	return bytes_to_frames(substream->runtime, pos);
+	return bytes_to_frames(runtime, pos);
 }
 EXPORT_SYMBOL_GPL(snd_dmaengine_pcm_pointer);
 
-- 
2.20.1