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

- From: Jie Deng \<hidden\>
- Date: 2021-03-24 04:01:32 
- List: virtualization
- Page: https://ratatoskr.run/virtualization/2021/03/6313186
- Thread: https://ratatoskr.run/linux-i2c/2021/03/6311697/t.md

```text

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.


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