Typically the codec drivers require setting up of Sysclk. Sometimes
presence of internal PLL can provide more options of Sysclk configuration.
Presently ASoC provides callbacks set_sysclk() and set_pll() in such
cases. However it comes with following limitations considering generic
machine drivers (simple-card or audio-graph-card):
1. The Sysclk source needs to be passed to set_sysclk() callback.
Presently simple-card or audio-graph-card card rely on default
source value (which is 0). If any other source needs to be used,
it is currently not possible.
2. The same would be true for codec PLL configuration as well, though
simple-card or audio-graph-card don't have support yet for the PLL
configuration.
Earlier attempt[0] to address above was not felt suitable. The suggestion
was to use standard clock based bindings instead.
This RFC series takes RT5659 as a reference and exposes clock relationships
via DT. **This is not in the final shape yet**, but I wanted to get some
valuable feedback to understand if the idea is right. If this appears fine,
this can be extended to other codecs (wherever necessary).
This does not completely remove the need of set_sysclk() callback because
the clock requirement (MCLK * fs) would come from the machine driver. But
machine driver need not worry about Sysclk source. It would be internally
managed by Codec via DT clock relationships.
[0] https://patchwork.kernel.org/project/alsa-devel/list/?series=438531&archive=both&state=*
Sameer Pujar (3):
ASoC: soc-pcm: tweak DPCM BE hw_param() call order
ASoC: rt5659: Expose internal clock relationships
ASoC: tegra: Get clock rate in consumer mode
sound/soc/codecs/rt5659.c | 257 +++++++++++++++++++++++++++++++++++++++--
sound/soc/codecs/rt5659.h | 9 ++
sound/soc/soc-pcm.c | 60 +++++++++-
sound/soc/tegra/tegra210_i2s.c | 25 ++--
4 files changed, 332 insertions(+), 19 deletions(-)
--
2.7.4
