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

From: "Jernej Škrabec" <jernej.skrabec@siol.net>
To: peron.clem@gmail.com, Maxime Ripard <mripard@kernel.org>,
	Chen-Yu Tsai <wens@csie.org>, Rob Herring <robh+dt@kernel.org>,
	Mark Brown <broonie@kernel.org>,
	Liam Girdwood <lgirdwood@gmail.com>,
	Samuel Holland <samuel@sholland.org>
Cc: Jaroslav Kysela <perex@perex.cz>, Takashi Iwai <tiwai@suse.com>,
	Marcus Cooper <codekipper@gmail.com>,
	alsa-devel@alsa-project.org, devicetree@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org, linux-sunxi@googlegroups.com
Subject: Re: [linux-sunxi] [PATCH 05/16] ASoc: sun4i-i2s: Add 20 and 24 bit support
Date: Wed, 02 Sep 2020 20:10:47 +0200	[thread overview]
Message-ID: <9148679.oVN3Z7rve9@kista> (raw)
In-Reply-To: <1e320dfd-9388-54b2-dba9-7def0bf4bbad@sholland.org>

Hi Samuel!

Dne petek, 10. julij 2020 ob 07:44:51 CEST je Samuel Holland napisal(a):
> On 7/4/20 6:38 AM, Clément Péron wrote:
> > From: Marcus Cooper <codekipper@gmail.com>
> > 
> > Extend the functionality of the driver to include support of 20 and
> > 24 bits per sample.
> > 
> > Signed-off-by: Marcus Cooper <codekipper@gmail.com>
> > Signed-off-by: Clément Péron <peron.clem@gmail.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.

I'm not sure what has WSS with physical width and DMA?

> 
> 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.

Allwinner DMA engines support only 1, 2, 4 and sometimes 8 bytes for bus 
width, so if sample is 24 bits in size, we have no other way but to transmit 
padding too.

Best regards,
Jernej

> 
> 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,