On 06/06/2019 11:22, Peter Ujfalusi wrote: ... >>>> It does sounds like that FIFO_SIZE == src/dst_maxburst in your case as >>>> well. >>> Not exactly equal. >>> ADMA burst_size can range from 1(WORD) to 16(WORDS) >>> FIFO_SIZE can be adjusted from 16(WORDS) to 1024(WORDS) [can vary in >>> multiples of 16] >> >> So I think that the key thing to highlight here, is that the as Sameer >> highlighted above for the Tegra ADMA there are two values that need to >> be programmed; the DMA client FIFO size and the max burst size. The ADMA >> has register fields for both of these. > > How does the ADMA uses the 'client FIFO size' and 'max burst size' > values and what is the relation of these values to the peripheral side > (ADMAIF)? Per Sameer's previous comment, the FIFO size is used by the ADMA to determine how much space is available in the FIFO. I assume the burst size just limits how much data is transferred per transaction. >> As you can see from the above the FIFO size can be much greater than the >> burst size and so ideally both of these values would be passed to the DMA. >> >> We could get by with just passing the FIFO size (as the max burst size) >> and then have the DMA driver set the max burst size depending on this, >> but this does feel quite correct for this DMA. Hence, ideally, we would >> like to pass both. >> >> We are also open to other ideas. > > I can not find public documentation (I think they are walled off by > registration), but correct me if I'm wrong: No unfortunately, you are not wrong here :-( > ADMAIF - peripheral side > - kind of a small DMA for audio preipheral(s)? Yes this is the interface to the APE (audio processing engine) and data sent to the ADMAIF is then sent across a crossbar to one of many devices/interfaces (I2S, DMIC, etc). Basically a large mux that is user configurable depending on the use-case. > - Variable FIFO size Yes. > - sends DMA request to ADMA per words >From Sameer's notes it says the ADMAIF send a signal to the ADMA per word, yes. > ADMA - system DMA > - receives the DMA requests from ADMAIF > - counts the requests > - based on some threshold of the counter it will send/read from ADMAIF? > - maxburst number of words probably? Sounds about right to me. > ADMA needs to know the ADMAIF's FIFO size because, it is the one who is > managing that FIFO from the outside, making sure that it does not over > or underrun? Yes. > And it is the one who sets the pace (in effect the DMA burst size - how > many bytes the DMA jumps between refills) of refills to the ADMAIF's FIFO? Yes. So currently, if you look at the ADMA driver (drivers/dma/tegra210-adma.c) you will see we use the src/dst_maxburst for the burst, but the FIFO size is hard-coded (see the TEGRA210_FIFO_CTRL_DEFAULT and TEGRA186_FIFO_CTRL_DEFAULT definitions). Ideally, we should not hard-code this but pass it. Given that there are no current users of the ADMA upstream, we could change the usage of the src/dst_maxburst, but being able to set the FIFO size as well would be ideal. Cheers Jon -- nvpublic
