Re: [PATCH v10] i2c: virtio: add a virtio i2c frontend driver

Jie Deng
2021-03-24T04:01:31Z

On 2021/3/24 11:52, Viresh Kumar wrote:
> On 24-03-21, 08:53, Jie Deng wrote:
>> On 2021/3/23 17:38, Viresh Kumar wrote:
>>> On 23-03-21, 14:31, Viresh Kumar wrote:
>>>> On 23-03-21, 22:19, Jie Deng wrote:
>>>>> +static int virtio_i2c_xfer(struct i2c_adapter *adap, struct i2c_msg *msgs, int num)
>>>>> +{
>>>>> + struct virtio_i2c *vi = i2c_get_adapdata(adap);
>>>>> + struct virtqueue *vq = vi->vq;
>>>>> + struct virtio_i2c_req *reqs;
>>>>> + unsigned long time_left;
>>>>> + int ret, nr;
>>>>> +
>>>>> + reqs = kcalloc(num, sizeof(*reqs), GFP_KERNEL);
>>>>> + if (!reqs)
>>>>> + return -ENOMEM;
>>>>> +
>>>>> + mutex_lock(&vi->lock);
>>>>> +
>>>>> + ret = virtio_i2c_send_reqs(vq, reqs, msgs, num);
>>>>> + if (ret == 0)
>>>>> + goto err_unlock_free;
>>>>> +
>>>>> + nr = ret;
>>>>> + reinit_completion(&vi->completion);
>>>> I think I may have found a possible bug here. This reinit_completion() must
>>>> happen before we call virtio_i2c_send_reqs(). It is certainly possible (surely
>>>> in corner cases) that virtio_i2c_msg_done() may get called right after
>>>> virtio_i2c_send_reqs() and before we were able to call reinit_completion(). And
>>>> in that case we will never see the completion happen at all.
>>>>
>>>>> + virtqueue_kick(vq);
>>> I may have misread this. Can the actually start before virtqueue_kick() is
>>> called ?
> I didn't write it properly here. I wanted to say,
>
> "Can the _transfer_ actually start before virtqueue_kick() is called ?"
>

It can't start until the virtqueue_kick() is called. Call virtqueue_kick
then wait.