linux-kernel - Re: [PATCH] ASoC: amd: acp: Adjust pdm dmic gain using module parameter

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Message-ID: <2025072814-stardom-anointer-0a62@gregkh>
Date: Mon, 28 Jul 2025 12:52:04 +0200
From: Greg KH <gregkh@...uxfoundation.org>
To: Venkata Prasad Potturu <venkataprasad.potturu@....com>
Cc: broonie@...nel.org, alsa-devel@...a-project.org,
	Vijendar.Mukunda@....com, Basavaraj.Hiregoudar@....com,
	Sunil-kumar.Dommati@....com, syed.sabakareem@....com,
	Liam Girdwood <lgirdwood@...il.com>,
	Jaroslav Kysela <perex@...ex.cz>, Takashi Iwai <tiwai@...e.com>,
	Mario Limonciello <mario.limonciello@....com>,
	Peter Zijlstra <peterz@...radead.org>,
	"open list:SOUND - SOC LAYER / DYNAMIC AUDIO POWER MANAGEM..." <linux-sound@...r.kernel.org>,
	open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ASoC: amd: acp: Adjust pdm dmic gain using module
 parameter

On Mon, Jul 28, 2025 at 03:12:27PM +0530, Venkata Prasad Potturu wrote:
> Adjust pdm dimc gain value using module param.
> In case of regressions for any users that the new pdm_gain value is
> too high and for additional debugging, introduce a module parameter
> that would let them configure it.
> 
> This parameter should be removed in the future:
>  * If it's determined that the parameter is not needed, just hardcode
>    the correct value as before
>  * If users do end up using it to debug and report different values
>    we should introduce a config knob that can have policy set by ucm.
> 
> Signed-off-by: Venkata Prasad Potturu <venkataprasad.potturu@....com>
> ---
>  sound/soc/amd/acp/acp-legacy-common.c | 3 ++-
>  sound/soc/amd/acp/acp-pdm.c           | 3 ++-
>  sound/soc/amd/acp/amd.h               | 6 +++++-
>  3 files changed, 9 insertions(+), 3 deletions(-)
> 
> diff --git a/sound/soc/amd/acp/acp-legacy-common.c b/sound/soc/amd/acp/acp-legacy-common.c
> index 57982d057c3a..dd804fb95790 100644
> --- a/sound/soc/amd/acp/acp-legacy-common.c
> +++ b/sound/soc/amd/acp/acp-legacy-common.c
> @@ -173,7 +173,8 @@ static void set_acp_pdm_clk(struct snd_pcm_substream *substream,
>  	/* Enable default ACP PDM clk */
>  	writel(PDM_CLK_FREQ_MASK, chip->base + ACP_WOV_CLK_CTRL);
>  	pdm_ctrl = readl(chip->base + ACP_WOV_MISC_CTRL);
> -	pdm_ctrl |= PDM_MISC_CTRL_MASK;
> +	pdm_ctrl &= ~ACP_WOV_GAIN_CONTROL;
> +	pdm_ctrl |= FIELD_PREP(ACP_WOV_GAIN_CONTROL, clamp(pdm_gain, 0, 3));
>  	writel(pdm_ctrl, chip->base + ACP_WOV_MISC_CTRL);
>  	set_acp_pdm_ring_buffer(substream, dai);
>  }
> diff --git a/sound/soc/amd/acp/acp-pdm.c b/sound/soc/amd/acp/acp-pdm.c
> index 1bfc34c2aa53..ffb622a7a69a 100644
> --- a/sound/soc/amd/acp/acp-pdm.c
> +++ b/sound/soc/amd/acp/acp-pdm.c
> @@ -38,7 +38,8 @@ static int acp_dmic_prepare(struct snd_pcm_substream *substream,
>  	/* Enable default DMIC clk */
>  	writel(PDM_CLK_FREQ_MASK, chip->base + ACP_WOV_CLK_CTRL);
>  	dmic_ctrl = readl(chip->base + ACP_WOV_MISC_CTRL);
> -	dmic_ctrl |= PDM_MISC_CTRL_MASK;
> +	dmic_ctrl &= ~ACP_WOV_GAIN_CONTROL;
> +	dmic_ctrl |= FIELD_PREP(ACP_WOV_GAIN_CONTROL, clamp(pdm_gain, 0, 3));
>  	writel(dmic_ctrl, chip->base + ACP_WOV_MISC_CTRL);
>  
>  	period_bytes = frames_to_bytes(substream->runtime,
> diff --git a/sound/soc/amd/acp/amd.h b/sound/soc/amd/acp/amd.h
> index cb8d97122f95..f2567e06ccd3 100644
> --- a/sound/soc/amd/acp/amd.h
> +++ b/sound/soc/amd/acp/amd.h
> @@ -130,7 +130,7 @@
>  #define PDM_DMA_INTR_MASK       0x10000
>  #define PDM_DEC_64              0x2
>  #define PDM_CLK_FREQ_MASK       0x07
> -#define PDM_MISC_CTRL_MASK      0x10
> +#define ACP_WOV_GAIN_CONTROL	GENMASK(4, 3)
>  #define PDM_ENABLE              0x01
>  #define PDM_DISABLE             0x00
>  #define DMA_EN_MASK             0x02
> @@ -138,6 +138,10 @@
>  #define PDM_TIMEOUT             1000
>  #define ACP_REGION2_OFFSET      0x02000000
>  
> +static int pdm_gain = 3;
> +module_param(pdm_gain, int, 0644);
> +MODULE_PARM_DESC(pdm_gain, "Gain control (0-3)");

This is not the 1990's, please do not add new module parameters, it will
not work for modern systems and is a horrible thing to attempt to
support over time :(

Please do this properly, with a per-device setting.

thanks,

greg k-h