Intel Atom I2C

Hi

I am trying to figure out how to get I2C support on Intel Atom x5
(Cherryview), which should be same for Baytrail platforms.

On the Serial I/O device (PCI device 24) there are 8 devices.
#0 is DMA controller
#1-7 are I2C controllers (1 & 2 available on GPIO pins).

I assume that all traffic to/from the I2C controllers must go via the DMA
controller although I'm not 100% sure.

In page 23 in the atom-z8000-datasheet-vol-2 there is a nice table of the
PCI configuration space.

On Linux they have
i2c/busses/i2c-designware-*
and
dma/dw/*
that takes care of the I2C and DMA parts.

The ichiic (ig4) driver seems to be working on this platform and looking
through the registers it seems to be basically the same as i2c-designware
driver, but it doesn't not detect any devices on the I2C bus (/dev/smbx).
(I have confirmed that the devices are recognized on Linux on the same
device.)

We also need a Mailbox (IOSF-SB MBI) driver and it is quite simple so I
have already ported this.

What is left to do I guess would be to implement a DMA driver that works
with ig4 or create a new ig4 driver that is extended to use the DMA
controller, and implement the DMA controller driver.

Implementing from scratch would be quite the undertaking. Can we leverage
any existing DMA infrastructure for this?

Any one interested in helping?

I have a board called "UP" which is very similar to Raspberry Pi but Intel
SoC. It has IC20 and IC21 available on the 40-pin connector.
Since it's Intel most stuff just works. Thanks to mmacy accelerated
graphics is also working (on separate branch).
It really is a great board for anyone who likes to tinker :)


References:
http://www.up-board.org/
http://lxr.linux.no/#linux+v4.6.2/drivers/i2c/busses
http://lxr.linux.no/#linux+v4.6.2/drivers/dma/dw
http://www.intel.com/content/www/us/en/processors/atom/atom-z8000-datasheet-vol-1.html
http://www.intel.com/content/www/us/en/processors/atom/atom-z8000-datasheet-vol-2.html

Other TODO stuff:
Port Imer's GPIO driver from DragonFly
Add support for S0ix sleep states (would be useful for all new Intel low
power laptops since Haswell)
And more...

Thanks!
/Johannes

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