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

[Jie Deng]

On 2020/9/3 18:20, Andy Shevchenko wrote:
> On Thu, Sep 03, 2020 at 01:34:45PM +0800, Jie Deng wrote:
> > Add an I2C bus driver for virtio para-virtualization.
> >
> > The controller can be emulated by the backend driver in
> > any device model software by following the virtio protocol.
> >
> > This driver communicates with the backend driver through a
> > virtio I2C message structure which includes following parts:
> >
> > - Header: i2c_msg addr, flags, len.
> > - Data buffer: the pointer to the i2c msg data.
> > - Status: the processing result from the backend.
> >
> > People may implement different backend drivers to emulate
> > different controllers according to their needs. A backend
> > example can be found in the device model of the open source
> > project ACRN. For more information, please refer to
> > https://projectacrn.org.
> >
> > The virtio device ID 34 is used for this I2C adpter since IDs
> > before 34 have been reserved by other virtio devices.
> Seems it's slightly different version to what I have reviewed internally.
> My comments below. (I admit that some of them maybe new)
>
> ...

Yeah... Some new devices have been added into the virtio spec during 
these days.


> > +/**
> > + * struct virtio_i2c_hdr - the virtio I2C message header structure
> > + * @addr: i2c_msg addr, the slave address
> > + * @flags: i2c_msg flags
> > + * @len: i2c_msg len
> > + */
> > +struct virtio_i2c_hdr {
> > +	__virtio16 addr;
> > +	__virtio16 flags;
> > +	__virtio16 len;
> > +} __packed;
> As Misha noticed and somewhere I saw 0-day reports these should be carefully
> taken care of.
>
> ...

Sure. Will fix these.


> > +static int virtio_i2c_xfer(struct i2c_adapter *adap, struct i2c_msg *msgs, int num)
> > +{
> > +	struct virtio_i2c *vi = i2c_get_adapdata(adap);
> > +	struct virtio_i2c_msg *vmsg_o, *vmsg_i;
> > +	struct virtqueue *vq = vi->vq;
> > +	unsigned long time_left;
> > +	int len, i, ret = 0;
> > +
> > +	vmsg_o = kzalloc(sizeof(*vmsg_o), GFP_KERNEL);
> > +	if (!vmsg_o)
> > +		return -ENOMEM;
> > +
> > +	mutex_lock(&vi->i2c_lock);
> > +	vmsg_o->buf = NULL;
> > +	for (i = 0; i < num; i++) {
> > +		ret = virtio_i2c_add_msg(vq, vmsg_o, &msgs[i]);
> > +		if (ret) {
> > +			dev_err(&adap->dev, "failed to add msg[%d] to virtqueue.\n", i);
> > +			goto err_unlock_free;
> break;

OK.


> > +		}
> > +
> > +		virtqueue_kick(vq);
> > +
> > +		time_left = wait_for_completion_timeout(&vi->completion, adap->timeout);
> > +		if (!time_left) {
> > +			dev_err(&adap->dev, "msg[%d]: addr=0x%x timeout.\n", i, msgs[i].addr);
> > +			ret = i;
> > +			goto err_unlock_free;
> break;
>
> And so on.
OK.
> > +		}
> > +
> > +		vmsg_i = (struct virtio_i2c_msg *)virtqueue_get_buf(vq, &len);
> > +		if (vmsg_i) {
> > +			/* vmsg_i should point to the same address with vmsg_o */
> > +			if (vmsg_i != vmsg_o) {
> > +				dev_err(&adap->dev, "msg[%d]: addr=0x%x virtqueue error.\n",
> > +					i, vmsg_i->hdr.addr);
> > +				ret = i;
> > +				goto err_unlock_free;
> > +			}
> > +			if (vmsg_i->status != VIRTIO_I2C_MSG_OK) {
> > +				dev_err(&adap->dev, "msg[%d]: addr=0x%x error=%d.\n",
> > +					i, vmsg_i->hdr.addr, vmsg_i->status);
> > +				ret = i;
> > +				goto err_unlock_free;
> > +			}
> > +			if ((vmsg_i->hdr.flags & I2C_M_RD) && vmsg_i->hdr.len)
> > +				memcpy(msgs[i].buf, vmsg_i->buf, vmsg_i->hdr.len);
> > +
> > +			kfree(vmsg_i->buf);
> > +			vmsg_i->buf = NULL;
> > +		}
> > +		reinit_completion(&vi->completion);
> > +	}
> > +	if (i == num)
> > +		ret = num;
> And this conditional seems a dup of the for-loop successfully iterating over
> entire queue.
You are right.
We may save several lines of code by using "Return (ret<0) ? ret : i" at 
the end.


> > +err_unlock_free:
> Redundant.
OK.
> > +	mutex_unlock(&vi->i2c_lock);
> > +	kfree(vmsg_o->buf);
> > +	kfree(vmsg_o);
> > +	return ret;
> > +}
> ...
>
> > +	vi->adap.timeout = HZ / 10;
> + Blank line.
OK.
> > +	ret = i2c_add_adapter(&vi->adap);
> > +	if (ret) {
> > +		dev_err(&vdev->dev, "failed to add virtio-i2c adapter.\n");
> > +		virtio_i2c_del_vqs(vdev);
> Usually we do clean up followed by message.
I will change the order. Thank you.
> > +	}
> > +
> > +	return ret;