> On 9. 6. 2022, at 17:16, Mark Brown <broonie@xxxxxxxxxx> wrote: > > On Thu, Jun 09, 2022 at 04:09:57PM +0200, Martin Povišer wrote: >>> On 9. 6. 2022, at 15:33, Mark Brown <broonie@xxxxxxxxxx> wrote: > >>>> + /* >>>> + * Primary FE >>>> + * >>>> + * The mclk/fs ratio at 64 for the primary frontend is important >>>> + * to ensure that the headphones codec's idea of left and right >>>> + * in a stereo stream over I2S fits in nicely with everyone else's. >>>> + * (This is until the headphones codec's driver supports >>>> + * set_tdm_slot.) >>>> + * >>>> + * The low mclk/fs ratio precludes transmitting more than two >>>> + * channels over I2S, but that's okay since there is the secondary >>>> + * FE for speaker arrays anyway. >>>> + */ >>>> + .mclk_fs = 64, >>>> + }, > >>> This seems weird - it looks like it's confusing MCLK and the bit clock >>> for the audio bus. These are two different clocks. Note that it's very >>> common for devices to require a higher MCLK/fs ratio to deliver the best >>> audio performance, 256fs is standard. > >> On these machines we are not producing any other clock for the codecs >> besides the bit clock, so I am using MCLK interchangeably for it. (It is >> what the sample rate is derived from after all.) > > Please don't do this, you're just making everything needlessly hard to > understand by using standard terminology inappropriately and there's a > risk of breakage further down the line with drivers implementing the > standard ops. OK >> One of the codec drivers this is to be used with (cs42l42) expects to be >> given the I2S bit clock with > >> snd_soc_dai_set_sysclk(dai, 0, mclk, SND_SOC_CLOCK_IN); > > That's very, very non-standard... > >> I can rename mclk to bclk in all of the code to make it clearer maybe. >> Also the platform driver can take the bit clock value from set_bclk_ratio, >> instead of set_sysclk from where it takes it now. The cs42l42 driver I can >> patch too to accept set_bclk_ratio. > > ...indeed, set_bclk_ratio() is a better interface for setting the bclk > ratio - the CODEC driver should really be doing that as well. OK, adding that to my TODOs. >>> This shouldn't be open coded in a driver, please factor it out into the >>> core so we've got an API for "set limit X on control Y" then call that. > >> There’s already snd_soc_limit_volume, but it takes a fixed control name. >> Can I extend it to understand patterns beginning with a wildcard, like >> '* Amp Gain Volume’? > > Or add a new call that does that. OK
