Hi Wolfram,

On Mon, 2015-05-18 at 08:37 +0200, Wolfram Sang wrote:

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+		rpaddr = dma_map_single(i2c->adap.dev.parent, msgs->buf,
+						msgs->len, DMA_FROM_DEVICE);

I think you shouldn't use the adapter device here and later, but the dma
channel device.

In MTK SoC, each I2C controller has its own DMA, and this DMA can't be
used by other hardware.
So I tend to use DMA directly, not through DMA channel.
Even so, "i2c->adap.dev.parent" is not suitable here. I will change to
use i2c->dev here. (Reference i2c-at91.c).

The better reference would be i2c-sh_mobile.c, especially commit
8cfcae9f0595bf0d145a67cfaa1051804a301d7c ("i2c: sh_mobile: use proper
device for mapping DMA memory") ;) The request to use the DMA channel
device came from the DMA folks, so if there is no real reason for an
exception, please use the channel device.

sh_mobile already implement dmaengine, so its I2C driver can use dma
channel.
But Mediatek SoC don't have "generic" DMA engine, Each DMA belong to
specific hardware, so dmaengine is not necessary, and not suitable for
our I2C controller.In other words, dma dev can be considered as part of
I2C controller dev.

Eddie