linux-kernel - Re: [PATCH v11] i2c: virtio: add a virtio i2c frontend driver

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Date:   Fri, 2 Jul 2021 15:15:18 +0800
From:   Jie Deng <jie.deng@...el.com>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     Wolfram Sang <wsa@...nel.org>, linux-i2c@...r.kernel.org,
        virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org, mst@...hat.com, arnd@...db.de,
        jasowang@...hat.com, andriy.shevchenko@...ux.intel.com,
        yu1.wang@...el.com, shuo.a.liu@...el.com, conghui.chen@...el.com,
        stefanha@...hat.com
Subject: Re: [PATCH v11] i2c: virtio: add a virtio i2c frontend driver


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.