Jon, On 06/06/2019 15.37, Jon Hunter wrote: >> 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. Hrm, it is still not clear how all of these fits together. What happens if you configure ADMA side: BURST = 10 TX/RXSIZE = 100 (100 * 64 bytes?) /* FIFO_SIZE? */ *THRES = 5 And if you change the *THRES to 10? And if you change the TX/RXSIZE to 50 (50 * 64 bytes?) And if you change the BURST to 5? In other words what is the relation between all of these? There must be a rule and constraints around these and if we do really need a new parameter for ADMA's FIFO_SIZE I'd like it to be defined in a generic way so others could benefit without 'misusing' a fifo_size parameter for similar, but not quite fifo_size information. - Péter Texas Instruments Finland Oy, Porkkalankatu 22, 00180 Helsinki. Y-tunnus/Business ID: 0615521-4. Kotipaikka/Domicile: Helsinki
