Virtualization - Jul 2021 - [PATCH v11] i2c: virtio: add a virtio i2c frontend driver

On 02-07-21, 14:52, Jie Deng wrote:
> This is not efficient. If adding the ith request to the queue fails, we can
> still send
> 
> the requests before it.
Not really. Normally the requests which are sent together by clients, are linked
together, like a state machine. So if the first one is sent, but not the second
one, then there is not going to be any meaningful result of that.

The i2c core doesn't club requests together from different clients in a
single
i2c_transfer() call. So you must assume i2c_transfer(), irrespective of the
number of underlying messages in it, as atomic. If you fail, the client is going
to retry everything again or assume it failed completely.
> We don't need to know if it fails here (adding to
> the queue)
> 
> or there (later in the host). The "master_xfer" just need to
return final
> number of
> 
> messages successfully processed.
No, that isn't going to help and it is rather inefficient, trying to send
transfer when we already know part of it failed.

-- 
viresh

On 2021/7/2 14:56, Viresh Kumar wrote:
> On 02-07-21, 14:52, Jie Deng wrote:
>> This is not efficient. If adding the ith request to the queue fails, we
can
>> still send
>>
>> the requests before it.
> Not really. Normally the requests which are sent together by clients, are
linked
> together, like a state machine. So if the first one is sent, but not the
second
> one, then there is not going to be any meaningful result of that.
>
> The i2c core doesn't club requests together from different clients in a
single
> i2c_transfer() call. So you must assume i2c_transfer(), irrespective of the
> number of underlying messages in it, as atomic. If you fail, the client is
going
> to retry everything again or assume it failed completely.

Then what is the need to design this interface as "return the number of 
messages successfully
processed, or a negative value on error". Just return success or fail is 
enough.

Here, we didn't break the contract with the interface
"master_xfer", so
if there is a problem then
the contract may be the problem.