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Date: Fri, 28 Feb 2014 13:03:52 +0100 From: Marek Vasut <marex@...x.de> To: Yao Yuan <yao.yuan@...escale.com> Cc: "linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>, "wsa@...-dreams.de" <wsa@...-dreams.de>, "mark.rutland@....com" <mark.rutland@....com>, "shawn.guo@...aro.org" <shawn.guo@...aro.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org> Subject: Re: [PATCH 1/3] i2c: add DMA support for freescale i2c driver 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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