Re: I2C adapters protocol deviation

[Hans de Goede <hdegoede-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>]

Hi,

On 04/04/2014 02:26 PM, Wolfram Sang wrote:
> 
>> So what we really have is a single slave i2c host sort of. At least
>> we could model it like that. The host could be told which address to
>> listen to (and which single i2c write to do to init the pmic) through
>> devicetree and then all the differences would be hidden in the host
>> driver, ie we would check the slave-address and if it is not the single
>> one we support, we just return the appropriate error for a device not
>> acking, and everything should work as a regular i2c host which
>> only supports i2c_smbus_read_byte and i2c_smbus_write_byte.
> 
> I'd think we need a new message flag like I2C_M_PUSHPULL which says that
> this message has only the direction bit instead of the address and needs
> a parity bit afterwards. In addition to that, we need a new
> functionality flag I2C_FUNC_PUSHPULL which means the host driver can
> handle those messages. So, the PMIC driver could query support for
> I2C_FUNC_SMBUS_BYTE | I2C_FUNC_PUSHPULL and if successful send messages
> using smbus functions with the new flag set.

Thanks for the input this sounds good, I guess we'll give this a shot
when we get around to coding up support for the p2wi block in the A31.

> Not sure about the I2C-to-PushPull switch: Is it 100% host configuration
> or does it also depend on the one slave attached? 

The datasheet we've suggests that it actually influences the one slave
attached. Note that u-boot on this machines will likely already have made
the switch, but I guess we don't want to count on that.

> Are there some datasheets available?

The AXP221 is documented here:
http://linux-sunxi.org/AXP221
This is translated by one of our community members from a Chinese datasheet.

The P2WI interface is (somewhat) documented in the A31 datasheet, but we cannot
share that in public.

Regards,

Hans