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

Jie Deng
2020-09-04T06:09:04Z

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;
>