Hi Marek, > On Friday, February 28, 2014 at 06:19:18 AM, Yao Yuan wrote: > > [...] > > > > > @@ -213,6 +238,7 @@ static struct imx_i2c_hwdata vf610_i2c_hwdata > > > > = { > > > > > > > > .ndivs = ARRAY_SIZE(vf610_i2c_clk_div), > > > > .i2sr_clr_opcode = I2SR_CLR_OPCODE_W1C, > > > > .i2cr_ien_opcode = I2CR_IEN_OPCODE_0, > > > > > > > > + .has_dma_support = true, > > > > > > So why exactly don't we have a DT prop for determining whether the > > > controller has DMA support ? > > > > > > What about the other controllers, do they not support DMA for some > > > specific reason? Please elaborate on that, thank you ! > > > > Sorry for my fault. I will modify it. > > I would prefer if you could explain why other controllers do have DMA > disabled even if the hardware does support the DMA operation. > Well, Because of the I2C in I.MX hardware don't support the DMA operation. But here I also think has_dma_support isn't necessary. > > > Also, can the DMA not do full-duplex operation ? What I see here is > > > just > > > half- duplex operations , one for RX and the other one for TX . > > > > Yes, here have two dma channels, one for RX and the other one for TX. > > When we request the channel we should determine it for TX or RX. > > Sorry, I don't quite understand this. If you have two DMA channels, can > you not use them both to do full-duplex SPI transfer ? > Sorry, There are also hard for me. I don't understand what is full-duplex for dma? A DMA engine can only read or write at the same time. And a dma channel request for only DMA_MEM_TO_DEV or DMA_DEV_TO_MEM almost. Also i2c is a half-duplex bus. {.n++%ݶw{.n+{G{ayʇڙ,jfhz_(階ݢj"mG?&~iOzv^m ?I