Re: [PATCH v2] ASoC: bcm2835: Add 8 channel (multitrack) capability

[Charles Keepax <ckeepax@opensource.wolfsonmicro.com>]

On Mon, Feb 13, 2017 at 10:27:15AM +1100, Matt Flax wrote:
> This patch adds multitrack capability if in DSP mode A and the
> codec is master.
> 
> In bcm2835_i2s_startup, snd_pcm_hw_constraint_minmax is used to set
> max channels to 8 if both SND_SOC_DAIFMT_CBM_CFM and
> SND_SOC_DAIFMT_DSP_A are set. Otherwise, max channels is set to 2.
> Min channels is always set to 2. These settings are accomplished
> using the SNDRV_PCM_HW_PARAM_CHANNELS variable.
> 
> In bcm2835_i2s_shutdown max channels is set to 2 by default.
> 
> In bcm2835_i2s_hw_params, DSP mode A format is now an option.
> Before replicating the format variable (from ch2 to ch1) for
> register loading, requested channels are checked to be either 2 or 8.
> This can be expaneded later to accomodate other channel counts if
> supported by the sound card hardware.
> 
> Signed-off-by: Matt Flax <flatmax@flatmax.org>
> ---
<snip>
> @@ -312,6 +313,7 @@ static int bcm2835_i2s_hw_params(struct snd_pcm_substream *substream,
>  
>  	switch (params_channels(params)) {
>  	case 2:
> +	case 8:
>  		format = BCM2835_I2S_CH1(format) | BCM2835_I2S_CH2(format);
>  		format |= BCM2835_I2S_CH1(BCM2835_I2S_CHPOS(ch1pos));
>  		format |= BCM2835_I2S_CH2(BCM2835_I2S_CHPOS(ch2pos));
> @@ -526,7 +528,16 @@ static int bcm2835_i2s_startup(struct snd_pcm_substream *substream,
>  	regmap_update_bits(dev->i2s_regmap, BCM2835_I2S_CS_A_REG,
>  			BCM2835_I2S_STBY, BCM2835_I2S_STBY);
>  
> -	return 0;
> +	/* Set the max channels to 8 if the codec is master and
> +	 * we are in DSP A mode. Otherwise only allow 2 channels.
> +	 */
> +	if (dev->fmt &
> +		(SND_SOC_DAIFMT_CBM_CFM | SND_SOC_DAIFMT_DSP_A))
> +		return snd_pcm_hw_constraint_minmax(substream->runtime,
> +			SNDRV_PCM_HW_PARAM_CHANNELS, 2, 8);

Would it be worth using snd_pcm_hw_constraint_list here? We are
going to error out of hw_params if the user requests anything
other than 2 or 8 channels so we should probably just constrain
to those two.

> +	else
> +		return snd_pcm_hw_constraint_minmax(substream->runtime,
> +			SNDRV_PCM_HW_PARAM_CHANNELS, 2, 2);

snd_pcm_hw_constraint_single, it's exactly the same thing but I
guess we should probably use the helper if it exists.

>  }
>  
>  static void bcm2835_i2s_shutdown(struct snd_pcm_substream *substream,
> @@ -549,6 +560,10 @@ static void bcm2835_i2s_shutdown(struct snd_pcm_substream *substream,
>  	 * not stop the clock when SND_SOC_DAIFMT_CONT
>  	 */
>  	bcm2835_i2s_stop_clock(dev);
> +
> +	/* Default to 2 channels */
> +	snd_pcm_hw_constraint_minmax(substream->runtime,
> +			SNDRV_PCM_HW_PARAM_CHANNELS, 2, 2);
>  }

ditto.

Thanks,
Charles