On Fri, Dec 01, 2017 at 02:02:29AM +0100, Maciej S. Szmigiero wrote: > > I will clean up the driver a bit and I think the change would be > > highly related to AC97 code. So I'll later need you review/test.
> From my perspective it would be great if the whole cleanup was in one > series, so the whole testing doesn't need to be repeated per patch > (it involves a lot of manual work). Understood. > >> Regarding a sample rate in AC'97 mode its effective value isn't really > >> controlled by the CPU (that is, SSI), but by a CODEC since it is > >> the CODEC which tells the CPU when it should send a next sample for > >> playback and when a next capture sample is ready. > >> There are no problems if they are different (as long as the CODEC > >> supports this, naturally, but it's up to its driver to restrict the > >> sample rate space accordingly). > > > > It's because CODEC drives the bit clock and framesync clock, isn't > > it? > > Strictly speaking, the frame sync is driven by the controller (SSI), > but it is simply the CODEC-provided bit clock divided by 256. > And the CODEC-provided bit clock is fixed at 12.288MHz by the AC'97 > specs. > > But every frame from CODEC also has 'TAG' bits which tell the > controller whether this frame contains valid capture samples or not. > If the capture sample rate currently programmed in CODEC is less > than 48kHz (the frame rate) it simply means that some of incoming > frames will contain 'TAG' bits indicating that these frames do not > contain valid capture samples (for example, if the capture rate is > 24kHz then only half of the frames, on average, will be marked by CODEC > as containing valid capture samples). > > The situation with playback is similar: the frame from CODEC also has > 'SLOTREQ' bits which tell the controller if it should send playback > samples (and which) in the next frame - for example, if the playback > rate is 24kHz then in half of the frames, on average, the CODEC will > request playback samples. > > Hope it is clear now. Thanks for the explain. It's clear now. Nicolin
