Re: [PATCH v1 2/4] ASoC: tac5xx2-sdw: add soundwire based codec driver

[Charles Keepax]

On Mon, Mar 23, 2026 at 02:40:42PM -0700, Pierre-Louis Bossart wrote:
> > +/* Convert dB to Q7.8 format (16-bit signed value) */
> > +static inline u16 db_to_q7_8(int db_value_times_100)
> > +{
> > +	u16 result = (u16)(((db_value_times_100 * 256) / 100) & 0xFFFF);
> > +	return result;
> > +}
> > +
> > +/* Convert Q7.8 format to dB*100 */
> > +static inline int q7_8_to_db_times_100(u16 q7_8_value)
> > +{
> > +	s16 signed_val = (s16)q7_8_value;
> > +
> > +	return (signed_val * 100) / 256;
> > +}
> 
> Didn't Charles Keepax add some macros for the Q7.8 format?

Me and Shuming Fan did some work on this in the SDCA class driver,
it is currently based on a slightly different system using the
TLV to map to dB's where as this code seems to present 100ths
of a dB directly. The problem with that approach however is you
tend to loose some precision as you generally don't end up with
a 1-to-1 mapping from control values to register values.

The helpers are not currently seperately exported although
no reason they couldn't be. q78_put_volsw and q78_get_volsw
in sdca_asoc.c.

Thanks,
Charles