Re: [PATCH v3 7/8] ASoC: qcom: apq8016_sbc: Add support for msm8976 SoC

[Stephan Gerhold]

On Wed, Jul 31, 2024 at 05:25:31PM +0200, Adam Skladowski wrote:
> Introduce support for audio card on MSM8976 platform.
> While MSM8976 falls into v1 category with MSM8916, digitial codec clock
> is not available in GCC so we have to set it in machine driver.
> For that reason for V1 clocks new boolean is added to check
> if we need to enable codec clock.
> 
> Signed-off-by: Adam Skladowski <a39.skl@xxxxxxxxx>
> ---
>  sound/soc/qcom/apq8016_sbc.c | 28 ++++++++++++++++++++++++++++
>  1 file changed, 28 insertions(+)
> 
> diff --git a/sound/soc/qcom/apq8016_sbc.c b/sound/soc/qcom/apq8016_sbc.c
> index 3ed35beb671a..8219d4d55625 100644
> --- a/sound/soc/qcom/apq8016_sbc.c
> +++ b/sound/soc/qcom/apq8016_sbc.c
> @@ -35,6 +35,7 @@ struct apq8016_sbc_data {
>  	struct snd_soc_jack jack;
>  	bool jack_setup;
>  	enum afe_clk_api q6afe_clk_ver;
> +	bool dig_cdc_mclk_en;
>  	int mi2s_clk_count[MI2S_COUNT];
>  };
>  
> @@ -242,6 +243,16 @@ static int msm8916_qdsp6_startup(struct snd_pcm_substream *substream)
>  
>  	if (++data->mi2s_clk_count[mi2s] > 1)
>  		return 0;
> +	/*
> +	 * On newer legacy SoC (MSM8976) lpass codec clocks are not available in gcc region
> +	 * so we have to request clock from machine driver using V1 API)
> +	 */
> +	if (data->q6afe_clk_ver == Q6AFE_CLK_V1 &&
> +	    data->dig_cdc_mclk_en) {
> +		ret = snd_soc_dai_set_sysclk(cpu_dai,  LPAIF_DIG_CLK, DEFAULT_MCLK_RATE, 0);
> +		if (ret)
> +			dev_err(card->dev, "Failed to enable LPAIF dig clk: %d\n", ret);
> +	}
>  
>  	ret = snd_soc_dai_set_sysclk(cpu_dai, qdsp6_get_clk_id(data, mi2s), MI2S_BCLK_RATE, 0);
>  	if (ret)
> @@ -267,6 +278,13 @@ static void msm8916_qdsp6_shutdown(struct snd_pcm_substream *substream)
>  	ret = snd_soc_dai_set_sysclk(cpu_dai, qdsp6_get_clk_id(data, mi2s), 0, 0);
>  	if (ret)
>  		dev_err(card->dev, "Failed to disable LPAIF bit clk: %d\n", ret);
> +
> +	if (data->q6afe_clk_ver == Q6AFE_CLK_V1 &&
> +	    data->dig_cdc_mclk_en) {
> +		ret = snd_soc_dai_set_sysclk(cpu_dai,  LPAIF_DIG_CLK, 0, 0);
> +		if (ret)
> +			dev_err(card->dev, "Failed to disable LPAIF dig clk: %d\n", ret);
> +	}
>  }

I'm a bit confused why this works correctly. The digital codec clock
(mclk) is needed whenever accessing registers of the digital codec
("qcom,msm8916-wcd-digital-codec"). This is why the clock is directly
assigned to it in the DT, so the codec driver can request it when
needed. The startup/shutdown callbacks in this patch are only called
during audio playback, while the codec registers might be accessed any
time e.g. when changing the volume mixers. Perhaps you are lucky not to
hit that, but if the clock is off at that point the device will crash or
hang.

Instead of requesting the clock here, we should assign it to the digital
codec in the DT. I think Otto's series also allowed that for the older
v1 firmware [1]. Can we work towards finishing that up instead? That
should be more reliable.

Thanks,
Stephan

[1]: https://lore.kernel.org/linux-arm-msm/20231029165716.69878-1-otto.pflueger@xxxxxxxxx/