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Subject: Re: [PATCH v11] i2c: virtio: add a virtio i2c frontend driver
To:     Viresh Kumar <viresh.kumar@linaro.org>
Cc:     Wolfram Sang <wsa@kernel.org>, linux-i2c@vger.kernel.org,
        virtualization@lists.linux-foundation.org,
        linux-kernel@vger.kernel.org, mst@redhat.com, arnd@arndb.de,
        jasowang@redhat.com, andriy.shevchenko@linux.intel.com,
        yu1.wang@intel.com, shuo.a.liu@intel.com, conghui.chen@intel.com,
        stefanha@redhat.com
References: <510c876952efa693339ab0d6cc78ba7be9ef6897.1625104206.git.jie.deng@intel.com>
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 <409b6cc3-3339-61b2-7f42-0c69b6486bb3@intel.com>
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From:   Jie Deng <jie.deng@intel.com>
Message-ID: <bdea419c-b450-f6b1-fff3-7df077b2abfc@intel.com>
Date:   Fri, 2 Jul 2021 15:15:18 +0800
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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.