On 04/03/2019 18:59, Sven Van Asbroeck wrote: > On Fri, Mar 1, 2019 at 7:36 AM Mark Brown <broonie@xxxxxxxxxx> wrote: >> >> >> As Russell outlined there's quite a bit of hopeful assumption in how >> ASoC handles the mapping of memory formats onto wire formats which works >> almost all the time but not always and definitely not through robust >> design > > Yes, many of the painful tradeoffs in this discussion would go away, if the > alsa negotiation infrastructure was 'bclk_ratio aware'. > > They say that a 100-line patch is often better than 1000 words. To help kick- > start a discussion, I offer a simple patch which adds bclk_ratio to > hw_params, which lets alsa 'negotiate' it the same way as the format, > channels, etc. > > Obviously this is completely flawed, as it exposes bclk_ratio to userspace thru > snd_pcm_hw_params. Userspace has no business even knowing about this on-wire > property. > > It may be flawed in a lot of other ways I can't see rn :) > > As far as a flawed suggestion goes, it seems to behave quite well on my system. > The bclk_ratio is nicely constrained within the cpu and codec's supported > ranges and rules, and the lowest supported value is picked before hw_params() > gets called. Which is at least channels * sample_width. > > Would there be a way to hide the bclk_ratio from userspace? > > Is it even worth taking this forward? How likely is it for alsa components > to care about the bclk_ratio? Maybe this is a tda998x one-off? > I am not the right person say if this should be taken forward. However, if we are going forward, I think we need to add bclk_rate to snd_pcm_hw_params too, since the available bclks affects the choice of bclk_ratios that are available. For instance if the bclk is generated from static clock with a simple divider then following equatios should always be satisfied: bclk_rate = clk_source_rate / clk_divider, where clk_divider = 0, 1, ..n sample_rate = bclk_rate / bclk_ratio The good news is that snd_pcm_hw_rule_add() should be able to cope with such cross dependencies. BR, Jyri -- Texas Instruments Finland Oy, Porkkalankatu 22, 00180 Helsinki. Y-tunnus/Business ID: 0615521-4. Kotipaikka/Domicile: Helsinki _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx https://mailman.alsa-project.org/mailman/listinfo/alsa-devel
