Re: Trying to write data to i2c bus

["Cédric Le Goater" <clegoate@redhat.com>]

On 2/19/24 18:14, Corey Minyard wrote:
> On Mon, Feb 19, 2024 at 04:53:47PM +0000, Paz Offer wrote:
>> Thank you very much Corey,
>>
>> I am simulating an external module that wants to communicate with the board management controller (BMC).
>> The real device will be connected to the board using i2c bus, and could initiate communication at any time, by sending bytes over the bus.
> 
> And you have a simulated BMC that can do this?  Or is the system running
> in qemu the BMC.
> 
>>
>> I am not sure whether the 'Master-side' (the side the initiating communication) needs to simulate a full i2c-master device, or whether my code could 'simply' write directly to the appropriate registers of the guest OS.
>> Are there some examples or documentation on how to implement something like this?
> 
> The aspeed i2c controller is capable of having another bus master on an
> I2C but, but it is the only host that can currently do it.
> 
> It is doable, the code is ther for multiple bus masters, but there is no
> device currently that does it.  I assume that is coming at some point,
> but no documentation exists on how to do it.
> 
> You can look at the git commits in hw/i2c around 37fa5ca42623 "hw/i2c:
> support multiple masters" for the changes that were done to support
> this.


There is an i2c-echo device implementing an I2C slave  and a test,
test_arm_ast2600_evb_buildroot in tests/avocado/ machine_aspeed.py,
using it on the ast2600-evb.


Thanks,

C.