On 06/06/2019 12:54, Peter Ujfalusi wrote: > > > On 06/06/2019 13.49, Jon Hunter wrote: >> >> 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. > > Sure, hardcoding is never good ;) > >> 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. > > Looking at the drivers/dma/tegra210-adma.c for the > TEGRA*_FIFO_CTRL_DEFAULT definition it is still not clear where the > remote FIFO size would fit. > There are fields for overflow and starvation(?) thresholds and TX/RX > size (assuming word length, 3 == 32bits?). The TX/RX size are the FIFO size. So 3 equates to a FIFO size of 3 * 64 bytes. > Both threshold is set to one, so I assume currently ADMA is > pushing/pulling data word by word. That's different. That indicates thresholds when transfers start. > Not sure what the burst size is used for, my guess would be that it is > used on the memory (DDR) side for optimized, more efficient accesses? That is the actual burst size. > My guess is that the threshold values are the counter limits, if the DMA > request counter reaches it then ADMA would do a threshold limit worth of > push/pull to ADMAIF. > Or there is another register where the remote FIFO size can be written > and ADMA is counting back from there until it reaches the threshold (and > pushes/pulling again threshold amount of data) so it keeps the FIFO > filled with at least threshold amount of data? > > I think in both cases the threshold would be the maxburst. > > I suppose you have the patch for adma on how to use the fifo_size > parameter? That would help understand what you are trying to achieve better. Its quite simple, we would just use the FIFO size to set the fields TEGRAXXX_ADMA_CH_FIFO_CTRL_TXSIZE/RXSIZE in the TEGRAXXX_ADMA_CH_FIFO_CTRL register. That's all. Jon -- nvpublic
