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

Viresh Kumar
2021-03-24T04:03:12Z

On 24-03-21, 12:00, Jie Deng wrote:
>
> 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.

Great, thanks for the confirmation. The code is fine then.

--
viresh