RE: [PATCH] soundwire: intel_auxdevice: add kernel parameter for mclk divider

["Liao, Bard" <bard.liao@xxxxxxxxx>]

> -----Original Message-----
> From: Vinod Koul <vkoul@xxxxxxxxxx>
> Sent: Sunday, August 18, 2024 3:24 PM
> To: Bard Liao <yung-chuan.liao@xxxxxxxxxxxxxxx>
> Cc: linux-sound@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; pierre-
> louis.bossart@xxxxxxxxxxxxxxx; Liao, Bard <bard.liao@xxxxxxxxx>
> 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@xxxxxxxxxxxxxxx>
> >
> > 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?

The parameter is only needed when a BIOS provides a MCLK rate which
does not match the actual rate. It is not a normal case and it happens rarely.
Is it really necessary to be documented in kernel-parameters.txt?

> 
> >
> > Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@xxxxxxxxxxxxxxx>
> > Signed-off-by: Bard Liao <yung-chuan.liao@xxxxxxxxxxxxxxx>
> > ---
> >  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