Hi Ryan, > Yes, I2C controller share the same dma engine. The original thought > can be enable in all i2c channel. But in AST2600 have ERRATA "I2C DMA > fails when DRAM bus is busy and it can not take DMA write data > immediately", So it means only 1 i2c bus can be enable for DMA mode. OK, this is a pretty important detail! I'd suggest putting it in the binding document. Anything in the cover letter will get lost after review. If there is documentation that would be useful for a DTS author, I'd suggest putting it in the binding. > It means only 1 bus channel can be enable DMA for use case. > That following example for board-specific selection. > It is description in cover-letter. > The following is board-specific design example. > Board A Board B > ------------------------- ------------------------ > > i2c bus#1(master/slave) <===fingerprint ===> i2c bus#x (master/slave)| > > i2c bus#2(master)-> tmp i2c device | | | > > i2c bus#3(master)-> adc i2c device | | | > ------------------------- ------------------------ > > - in bus#1 situation, you should use DMA mode. > Because bus#1 have trunk data needed for transfer, it can enable bus > dma mode to reduce cpu utilized. What is "trunk data" in this context? Is this just a statement about the amount of expected transfers? > - in bus#2/3 situation, you should use buffer/byte mode > bus#2/3 is small package transmit, it can enable buffer mode or byte > mode to reduce memory cache flush overhead. > Buffer mode is better, because byte mode have interrupt > overhead(interrupt per byte data transmit), > > -But if you more bus#4 that still have trunk data needed for transfer > (master/slave), > it also use buffer mode to transmit. Because bus#1 have been use for > DMA mode. So, it sounds like: - there's no point in using byte mode, as buffer mode provides equivalent functionality with fewer drawbacks (ie, less interrupt load) - this just leaves the dma and buffer modes - only one controller can use dma mode So: how about just a single boolean property to indicate "use DMA on this controller"? Something like aspeed,enable-dma? Or if DT binding experts can suggest something common that might be more suitable? Cheers, Jeremy
