[alsa-devel] [PATCH v9 3/4] ASoC: tda998x: add a codec to the HDMI transmitter

[Jean-Francois Moine]

On Sun, 11 Jan 2015 23:03:14 +0200
Jyri Sarha <jsarha at ti.com> wrote:

> Some more comments based on my - finally successful - attempt to use 
> this code with BBB HDMI audio.
> 
> On 01/07/2015 12:51 PM, Jean-Francois Moine wrote:
> > This patch adds a CODEC to the NXP TDA998x HDMI transmitter.
	[snip]
> > @@ -47,6 +52,10 @@ struct tda998x_priv {
> >   	struct drm_encoder *encoder;
> >
> >   	u8 audio_ports[2];
> > +#ifdef WITH_CODEC
> > +	u8 sad[3];			/* Short Audio Descriptor */
> > +	struct snd_pcm_hw_constraint_list rate_constraints;
> > +#endif
> 
> It feels a bit backwards to me to store these audio side variables here 
> in DRM side driver - especially the rate_constraint - and provide a 
> function (tda998x_get_audio_var()) for getting their individual 
> addresses to ASoC side. Wouldn't it be more straight forward to provide 
> functions for setting and getting the audio side data from a void 
> pointer in DRM side device drvdata?

Good idea. The rate_constraints would be allocated by the codec and set by a transmitter function.

	[snip]
> > diff --git a/include/sound/tda998x.h b/include/sound/tda998x.h
> > new file mode 100644
> > index 0000000..97cff30
> > --- /dev/null
> > +++ b/include/sound/tda998x.h
> > @@ -0,0 +1,23 @@
> > +#ifndef SND_TDA998X_H
> > +#define SND_TDA998X_H
> > +
> > +#include <sound/pcm.h>
> > +
> > +/* port indexes */
> > +#define PORT_NONE (-1)
> > +#define PORT_SPDIF 0
> > +#define PORT_I2S 1
> > +
> > +typedef int (*get_audio_var_t)(struct device *dev,
> > +				u8 **sad,
> > +			struct snd_pcm_hw_constraint_list **rate_constraints);
> > +typedef int (*set_audio_input_t)(struct device *dev,
> > +				int port_index,
> > +				unsigned sample_rate,
> > +				int sample_format);
> > +
> 
> Why don't you simply declare tda998x_get_audio_var() and 
> tda998x_set_audio_input() here and export them in DRM side driver? This 
> is a tda998x specific codec after all. I see no point to this this 
> function pointer typedef game, when the pointers are anyway stored to 
> global variables in ASoC the side module.

There cannot be both ways of function call with modules:
the transmitter may call exported functions of the codec,
but the codec cannot call exported functions of the transmitter.

	[snip]
> > +	snd_pcm_hw_constraint_minmax(runtime,
> > +				SNDRV_PCM_HW_PARAM_CHANNELS,
> > +				1, sad[SAD_MX_CHAN_I]);
> 
> SAD byte 1 bits 2-0 provides the maximum channel count _minus_one_. You 
> should _add_one_ to sad[SAD_MX_CHAN_I] when setting the constraint.

Right. Thanks.

	[snip]
> > +static struct snd_soc_dai_driver tda998x_dais[] = {
> > +	{
> > +		.name = "spdif-hifi",
> > +		.id = PORT_SPDIF,
> > +		.playback = {
> > +			.stream_name	= "HDMI SPDIF Playback",
> > +			.channels_min	= 1,
> > +			.channels_max	= 2,
> > +			.rates		= SNDRV_PCM_RATE_CONTINUOUS,
> > +			.rate_min	= 22050,
> > +			.rate_max	= 192000,
> > +			.formats	= TDA998X_FORMATS,
> > +		},
> > +		.ops = &tda998x_codec_ops,
> > +	},
> > +	{
> > +		.name = "i2s-hifi",
> > +		.id = PORT_I2S,
> > +		.playback = {
> > +			.stream_name	= "HDMI I2S Playback",
> > +			.channels_min	= 1,
> > +			.channels_max	= 8,
> > +			.rates		= SNDRV_PCM_RATE_CONTINUOUS,
> > +			.rate_min	= 5512,
> > +			.rate_max	= 192000,
> > +			.formats	= TDA998X_FORMATS,
> > +		},
> > +		.ops = &tda998x_codec_ops,
> > +	},
> > +};
> 
> Why do you use SNDRV_PCM_RATE_CONTINUOUS, when HDMI standard only 
> supports 32000, 44100, 48000, 88200, 96000, 176400, and 192000 Hz-rates?

Before I treated the EDID, I directly used these definitions,
and my TV display accepted many more rates as 22050 with S/PDIF input
or 7875 with I2S input.

> > +
> > +static const struct snd_soc_dapm_widget tda998x_widgets[] = {
> > +	SND_SOC_DAPM_OUTPUT("hdmi-out"),
> > +};
> > +static const struct snd_soc_dapm_route tda998x_routes[] = {
> > +	{ "hdmi-out", NULL, "HDMI I2S Playback" },
> > +	{ "hdmi-out", NULL, "HDMI SPDIF Playback" },
> > +};
> > +
> > +static struct snd_soc_codec_driver tda998x_codec_drv = {
> > +	.dapm_widgets = tda998x_widgets,
> > +	.num_dapm_widgets = ARRAY_SIZE(tda998x_widgets),
> > +	.dapm_routes = tda998x_routes,
> > +	.num_dapm_routes = ARRAY_SIZE(tda998x_routes),
> > +	.ignore_pmdown_time = true,
> > +};
> > +
> > +int tda9998x_codec_register(struct device *dev,
> > +			get_audio_var_t get_audio_var_i,
> > +			set_audio_input_t set_audio_input_i)
> > +{
> > +	get_audio_var = get_audio_var_i;
> > +	set_audio_input = set_audio_input_i;
> > +	return snd_soc_register_codec(dev,
> > +				&tda998x_codec_drv,
> > +				tda998x_dais, ARRAY_SIZE(tda998x_dais));
> 
> So this always registers a two DAI codec whether or not both the i2s and 
> spdif is used. The DT binding document could state that the DAI index 0 
> is always the spdif DAI and index 1 is the i2s DAI, or even better you 
> could #define them under include/dt-bindings/.
> 
> While you are at it, you could also mention the DAPM output name 
> "hdmi-out" for the codec in the DT-binding document.
	[snip]

This will be changed when using the graph of ports: the DAIs will be
dynamically created from the DT.

-- 
Ken ar c'hentañ	|	      ** Breizh ha Linux atav! **
Jef		|		http://moinejf.free.fr/