linux-kernel - Re: [linux-sunxi] [PATCH 05/16] ASoc: sun4i-i2s: Add 20 and 24 bit support

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Message-ID: <1e320dfd-9388-54b2-dba9-7def0bf4bbad@sholland.org>
Date:   Fri, 10 Jul 2020 00:44:51 -0500
From:   Samuel Holland <samuel@...lland.org>
To:     peron.clem@...il.com, Maxime Ripard <mripard@...nel.org>,
        Chen-Yu Tsai <wens@...e.org>, Rob Herring <robh+dt@...nel.org>,
        Mark Brown <broonie@...nel.org>,
        Liam Girdwood <lgirdwood@...il.com>
Cc:     Jaroslav Kysela <perex@...ex.cz>, Takashi Iwai <tiwai@...e.com>,
        Marcus Cooper <codekipper@...il.com>,
        Jernej Skrabec <jernej.skrabec@...l.net>,
        alsa-devel@...a-project.org, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-sunxi@...glegroups.com
Subject: Re: [linux-sunxi] [PATCH 05/16] ASoc: sun4i-i2s: Add 20 and 24 bit
 support

On 7/4/20 6:38 AM, Clément Péron wrote:
> From: Marcus Cooper <codekipper@...il.com>
> 
> Extend the functionality of the driver to include support of 20 and
> 24 bits per sample.
> 
> Signed-off-by: Marcus Cooper <codekipper@...il.com>
> Signed-off-by: Clément Péron <peron.clem@...il.com>
> ---
>  sound/soc/sunxi/sun4i-i2s.c | 11 +++++++++--
>  1 file changed, 9 insertions(+), 2 deletions(-)
> 
> diff --git a/sound/soc/sunxi/sun4i-i2s.c b/sound/soc/sunxi/sun4i-i2s.c
> index f78167e152ce..bc7f9343bc7a 100644
> --- a/sound/soc/sunxi/sun4i-i2s.c
> +++ b/sound/soc/sunxi/sun4i-i2s.c
> @@ -577,6 +577,9 @@ static int sun4i_i2s_hw_params(struct snd_pcm_substream *substream,
>  	case 16:
>  		width = DMA_SLAVE_BUSWIDTH_2_BYTES;
>  		break;
> +	case 32:
> +		width = DMA_SLAVE_BUSWIDTH_4_BYTES;
> +		break;

This breaks the sun4i variants, because sun4i_i2s_get_wss returns 4 for a 32 bit
width, but it needs to return 3.

As a side note, I wonder why we use the physical width (the spacing between
samples in RAM) to drive the slot width. S24_LE takes up 4 bytes per sample in
RAM, which we need for DMA. But I don't see why we would want to transmit the
padding over the wire. I would expect it to be transmitted the same as S24_3LE
(which has no padding). It did not matter before, because the only supported
format had no padding.

Regards,
Samuel

>  	default:
>  		dev_err(dai->dev, "Unsupported physical sample width: %d\n",
>  			params_physical_width(params));
> @@ -1063,6 +1066,10 @@ static int sun4i_i2s_dai_probe(struct snd_soc_dai *dai)
>  	return 0;
>  }
>  
> +#define SUN4I_FORMATS	(SNDRV_PCM_FMTBIT_S16_LE | \
> +			 SNDRV_PCM_FMTBIT_S20_LE | \
> +			 SNDRV_PCM_FMTBIT_S24_LE)
> +
>  static struct snd_soc_dai_driver sun4i_i2s_dai = {
>  	.probe = sun4i_i2s_dai_probe,
>  	.capture = {
> @@ -1070,14 +1077,14 @@ static struct snd_soc_dai_driver sun4i_i2s_dai = {
>  		.channels_min = 1,
>  		.channels_max = 8,
>  		.rates = SNDRV_PCM_RATE_8000_192000,
> -		.formats = SNDRV_PCM_FMTBIT_S16_LE,
> +		.formats = SUN4I_FORMATS,
>  	},
>  	.playback = {
>  		.stream_name = "Playback",
>  		.channels_min = 1,
>  		.channels_max = 8,
>  		.rates = SNDRV_PCM_RATE_8000_192000,
> -		.formats = SNDRV_PCM_FMTBIT_S16_LE,
> +		.formats = SUN4I_FORMATS,
>  	},
>  	.ops = &sun4i_i2s_dai_ops,
>  	.symmetric_rates = 1,
>