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

[Mario Limonciello <mario.limonciello@amd.com>]

On 7/28/2025 4:22 PM, Greg KH wrote:
> 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@amd.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

As the main purpose for this parameter is for being able to tune whether 
the property is correct, how about adding a debugfs file instead?

AFAICT it should just be a single register write, so debugfs to read 
current value and write the debugging value seems pretty straightforward.