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

[Jie Deng]

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.