On Friday, February 28, 2014 at 12:36:01 PM, Yao Yuan wrote:
> 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.
OK, got it now. Thanks!
> > > > 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?
Sorry, nevermind. I was confused by this and some SPI patches review. Like
Lothar (thanks!) pointed out, using only half-duplex operation is OK.
Best regards,
Marek Vasut
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