i2c_transfer & dma

i2c_transfer & dma

[Peter Hüwe]

Hi,

I was wondering if the buffer in an i2c_msg, passed to i2c_transfer must be 
dma-able i.e. dynamically allocated, like for USB?

The reason why I'm asking is because the e.g. the i2c_robotfuzz_osif usb-to-
i2c adapter passes the incoming data directly to a usb_control_msg which of 
course expects the buffer to be dma-able.

So the question is - does the user of i2c_transfer have to provide a dma-able 
buffer, or is the bus driver (like the robotfuzz one) expected to convert 
incoming buffer into a dma-able buffer?


Thanks,
Peter

Re: i2c_transfer & dma

[Wolfram Sang]

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> So the question is - does the user of i2c_transfer have to provide a dma-able 
> buffer, or is the bus driver (like the robotfuzz one) expected to convert 
> incoming buffer into a dma-able buffer?

As of now, this is an open question, sadly. I have a tendency to leave
it to the drivers (maybe with helper functions from the core), because
I2C and DMA is so uncommon. I need to work on I2C & DMA next month
anyhow, so I hope to dive into that topic, too. No promises, though. If
you want to look into it already, please go ahead. The issue was raised
here, too: http://patchwork.ozlabs.org/patch/220137/


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