ASoC: rockchip: i2s: Support mono capture
diff mbox

Message ID 20180105221242.22083-1-mka@chromium.org
State New
Headers show

Commit Message

Matthias Kaehlcke Jan. 5, 2018, 10:12 p.m. UTC
The Rockchip I2S controller only allows to configure even numbers of
capture channels. It is still possible to capture monophonic audio by
using dual-channel mode and ignoring the 'data' from the second
channel.

Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
---
 sound/soc/rockchip/rockchip_i2s.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

Comments

Matthias Kaehlcke Jan. 9, 2018, 12:01 a.m. UTC | #1
El Fri, Jan 05, 2018 at 02:12:42PM -0800 Matthias Kaehlcke ha dit:

> The Rockchip I2S controller only allows to configure even numbers of
> capture channels. It is still possible to capture monophonic audio by
> using dual-channel mode and ignoring the 'data' from the second
> channel.

Due to different issues in our audio recording path I couldn't test
this properly, and only looked at the .wav data in audacity, which
appeared to look ok. After putting some of the missing pieces
together and I noticed that mono capture doesn't work as intended,
the recorded audio is slowed down. I think this is because the I2S
controller keeps generating a two-channel stream, however the sound
system interprets it as a monophonic stream because of the channel
configuration.

Not sure if there is a clean solution for this if we can't tell the
hardware to generate a single-channel stream. Any suggestions or do
we have to revert the patch?

Sorry about the mess :(

> ---
>  sound/soc/rockchip/rockchip_i2s.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/sound/soc/rockchip/rockchip_i2s.c b/sound/soc/rockchip/rockchip_i2s.c
> index 908211e1d6fc..cc22ab3d10dd 100644
> --- a/sound/soc/rockchip/rockchip_i2s.c
> +++ b/sound/soc/rockchip/rockchip_i2s.c
> @@ -328,6 +328,7 @@ static int rockchip_i2s_hw_params(struct snd_pcm_substream *substream,
>  		val |= I2S_CHN_4;
>  		break;
>  	case 2:
> +	case 1:
>  		val |= I2S_CHN_2;
>  		break;
>  	default:
> @@ -460,7 +461,7 @@ static struct snd_soc_dai_driver rockchip_i2s_dai = {
>  	},
>  	.capture = {
>  		.stream_name = "Capture",
> -		.channels_min = 2,
> +		.channels_min = 1,
>  		.channels_max = 2,
>  		.rates = SNDRV_PCM_RATE_8000_192000,
>  		.formats = (SNDRV_PCM_FMTBIT_S8 |
> @@ -654,7 +655,7 @@ static int rockchip_i2s_probe(struct platform_device *pdev)
>  	}
>  
>  	if (!of_property_read_u32(node, "rockchip,capture-channels", &val)) {
> -		if (val >= 2 && val <= 8)
> +		if (val >= 1 && val <= 8)
>  			soc_dai->capture.channels_max = val;
>  	}
>
Mark Brown Jan. 9, 2018, 4:39 p.m. UTC | #2
On Mon, Jan 08, 2018 at 04:01:15PM -0800, Matthias Kaehlcke wrote:

> Due to different issues in our audio recording path I couldn't test
> this properly, and only looked at the .wav data in audacity, which
> appeared to look ok. After putting some of the missing pieces
> together and I noticed that mono capture doesn't work as intended,
> the recorded audio is slowed down. I think this is because the I2S
> controller keeps generating a two-channel stream, however the sound
> system interprets it as a monophonic stream because of the channel
> configuration.

That seems odd - I'd expect underruns somewhere?

> Not sure if there is a clean solution for this if we can't tell the
> hardware to generate a single-channel stream. Any suggestions or do
> we have to revert the patch?

It sounds like a very standard problem with I2S devices, it's a
fundamentally stereo format after all.  If you can't get it to discard
the second channel there's probably not much doing.

Patch
diff mbox

diff --git a/sound/soc/rockchip/rockchip_i2s.c b/sound/soc/rockchip/rockchip_i2s.c
index 908211e1d6fc..cc22ab3d10dd 100644
--- a/sound/soc/rockchip/rockchip_i2s.c
+++ b/sound/soc/rockchip/rockchip_i2s.c
@@ -328,6 +328,7 @@  static int rockchip_i2s_hw_params(struct snd_pcm_substream *substream,
 		val |= I2S_CHN_4;
 		break;
 	case 2:
+	case 1:
 		val |= I2S_CHN_2;
 		break;
 	default:
@@ -460,7 +461,7 @@  static struct snd_soc_dai_driver rockchip_i2s_dai = {
 	},
 	.capture = {
 		.stream_name = "Capture",
-		.channels_min = 2,
+		.channels_min = 1,
 		.channels_max = 2,
 		.rates = SNDRV_PCM_RATE_8000_192000,
 		.formats = (SNDRV_PCM_FMTBIT_S8 |
@@ -654,7 +655,7 @@  static int rockchip_i2s_probe(struct platform_device *pdev)
 	}
 
 	if (!of_property_read_u32(node, "rockchip,capture-channels", &val)) {
-		if (val >= 2 && val <= 8)
+		if (val >= 1 && val <= 8)
 			soc_dai->capture.channels_max = val;
 	}