Re: [Qemu-devel] [PATCH V2 1/3] exynos4210: add Exynos4210 i2c implementation

[Igor Mitsyanko <i.mitsyanko@samsung.com>]

On 03/21/2012 03:55 PM, Peter Maydell wrote:
> On 15 March 2012 07:35, Igor Mitsyanko<i.mitsyanko@samsung.com>  wrote:
>> Create 9 exynos4210 i2c interfaces.
>>
>> Signed-off-by: Igor Mitsyanko<i.mitsyanko@samsung.com>
>
> Mostly this looks OK but I still find the i2c slave stuff
> odd -- should the controller really register itself as
> a slave on its own bus? Doesn't this mean that the
> controller can effectively try to talk to itself? Does
> the hardware let you do that?
>

Controller's master and slave i2c interfaces operate on the same single 
bus, so I think it should. It can't talk to itself because controller's 
two modes of operation are mutually exclusive. As I said, I took this 
approach from pxa i2c implementation, the only difference is that they 
register slave interface on a separate bus, but I think it's not right 
to do that.

> I suspect that what's happening here is that the hardware
> lets you put the i2c controller into slave mode so some
> other device on the bus can be a master. But QEMU's
> i2c bus abstraction doesn't cover that use case at all...
>

Yes, I saw this statement in hw/i2c.h (and probably cpu i2c controller 
will never be used as i2c slave device by anyone), but I think we still 
have to implement devices exactly like they described in documentation.

-- 
Mitsyanko Igor
ASWG, Moscow R&D center, Samsung Electronics
email: i.mitsyanko@samsung.com