linux-kernel - Re: [PATCH] soundwire: intel_auxdevice: add kernel parameter for mclk divider

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Message-ID: <ZsGhdFm8nYkm5Y5w@vaman>
Date: Sun, 18 Aug 2024 12:53:32 +0530
From: Vinod Koul <vkoul@...nel.org>
To: Bard Liao <yung-chuan.liao@...ux.intel.com>
Cc: linux-sound@...r.kernel.org, linux-kernel@...r.kernel.org,
	pierre-louis.bossart@...ux.intel.com, bard.liao@...el.com
Subject: Re: [PATCH] soundwire: intel_auxdevice: add kernel parameter for
 mclk divider

On 06-08-24, 16:38, Bard Liao wrote:
> From: Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
> 
> Add a kernel parameter to work-around discrepancies between hardware
> and platform firmware, it's not unusual to see e.g. 38.4MHz listed in
> _DSD properties as the SoundWire clock source, but the hardware may be
> based on a 19.2 MHz mclk source.

I think this should be documented in kernel-parameters.txt?

> 
> Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
> Signed-off-by: Bard Liao <yung-chuan.liao@...ux.intel.com>
> ---
>  drivers/soundwire/intel_auxdevice.c | 12 ++++++++++--
>  1 file changed, 10 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/soundwire/intel_auxdevice.c b/drivers/soundwire/intel_auxdevice.c
> index dff49c5ce5b3..e372195b07b3 100644
> --- a/drivers/soundwire/intel_auxdevice.c
> +++ b/drivers/soundwire/intel_auxdevice.c
> @@ -41,6 +41,10 @@ static int md_flags;
>  module_param_named(sdw_md_flags, md_flags, int, 0444);
>  MODULE_PARM_DESC(sdw_md_flags, "SoundWire Intel Master device flags (0x0 all off)");
>  
> +static int mclk_divider;
> +module_param_named(sdw_mclk_divider, mclk_divider, int, 0444);
> +MODULE_PARM_DESC(sdw_mclk_divider, "SoundWire Intel mclk divider");
> +
>  struct wake_capable_part {
>  	const u16 mfg_id;
>  	const u16 part_id;
> @@ -142,8 +146,12 @@ static int sdw_master_read_intel_prop(struct sdw_bus *bus)
>  				 "intel-sdw-ip-clock",
>  				 &prop->mclk_freq);
>  
> -	/* the values reported by BIOS are the 2x clock, not the bus clock */
> -	prop->mclk_freq /= 2;
> +	if (mclk_divider)
> +		/* use kernel parameter for BIOS or board work-arounds */
> +		prop->mclk_freq /= mclk_divider;
> +	else
> +		/* the values reported by BIOS are the 2x clock, not the bus clock */
> +		prop->mclk_freq /= 2;
>  
>  	fwnode_property_read_u32(link,
>  				 "intel-quirk-mask",
> -- 
> 2.43.0

-- 
~Vinod