Re: [PATCH v8] i2c: virtio: add a virtio i2c frontend driver

[Jie Deng]

On 2021/3/19 13:53, Viresh Kumar wrote:
> On 16-03-21, 18:35, Jie Deng wrote:
> > +++ b/drivers/i2c/busses/i2c-virtio.c
> > +static int virtio_i2c_send_reqs(struct virtqueue *vq,
> > +				struct virtio_i2c_req *reqs,
> > +				struct i2c_msg *msgs, int nr)
> > +{
> > +	struct scatterlist *sgs[3], out_hdr, msg_buf, in_hdr;
> > +	int i, outcnt, incnt, err = 0;
> > +
> > +	for (i = 0; i < nr; i++) {
> > +		if (!msgs[i].len)
> > +			break;
> > +
> > +		/*
> > +		 * Only 7-bit mode supported for this moment. For the address format,
> > +		 * Please check the Virtio I2C Specification.
> > +		 */
> > +		reqs[i].out_hdr.addr = cpu_to_le16(msgs[i].addr << 1);
> > +
> > +		if (i != nr - 1)
> > +			reqs[i].out_hdr.flags = cpu_to_le32(VIRTIO_I2C_FLAGS_FAIL_NEXT);
> > +
> > +		outcnt = incnt = 0;
> > +		sg_init_one(&out_hdr, &reqs[i].out_hdr, sizeof(reqs[i].out_hdr));
> > +		sgs[outcnt++] = &out_hdr;
> > +
> > +		reqs[i].buf = i2c_get_dma_safe_msg_buf(&msgs[i], 1);
> You allocate a buffer here, lets see if they are freeing properly or not (I
> remember that I gave same feedback earlier as well, but anyway).


"MAY" allocate a buffer here.


> > +		if (!reqs[i].buf)
> > +			break;
> > +
> > +		sg_init_one(&msg_buf, reqs[i].buf, msgs[i].len);
> > +
> > +		if (msgs[i].flags & I2C_M_RD)
> > +			sgs[outcnt + incnt++] = &msg_buf;
> > +		else
> > +			sgs[outcnt++] = &msg_buf;
> > +
> > +		sg_init_one(&in_hdr, &reqs[i].in_hdr, sizeof(reqs[i].in_hdr));
> > +		sgs[outcnt + incnt++] = &in_hdr;
> > +
> > +		err = virtqueue_add_sgs(vq, sgs, outcnt, incnt, &reqs[i], GFP_KERNEL);
> > +		if (err < 0) {
> > +			pr_err("failed to add msg[%d] to virtqueue.\n", i);
> > +			i2c_put_dma_safe_msg_buf(reqs[i].buf, &msgs[i], false);
> On failure here, you freed the buffers for request "i" but not others..


Others still need to be sent and then be freed.


> > +			break;
> > +		}
> > +	}
> > +
> > +	return i;
> > +}
> > +
> > +static int virtio_i2c_complete_reqs(struct virtqueue *vq,
> > +					struct virtio_i2c_req *reqs,
> > +					struct i2c_msg *msgs, int nr)
> > +{
> > +	struct virtio_i2c_req *req;
> > +	unsigned int len;
> > +	int i, j;
> > +
> > +	for (i = 0; i < nr; i++) {
> > +		req = virtqueue_get_buf(vq, &len);
> > +		if (!(req && req == &reqs[i])) {
> > +			pr_err("msg[%d]: addr=0x%x is out of order.\n", i, msgs[i].addr);
> > +			break;
> Since you break here, what will happen to the buffer ? I thought
> virtqueue_get_buf() will return a req only once and then you can't access it ?


Will refine it along with the latter loop.


> > +		}
> > +
> > +		if (req->in_hdr.status != VIRTIO_I2C_MSG_OK) {
> > +			pr_err("msg[%d]: addr=0x%x backend error.\n", i, msgs[i].addr);
> > +			break;
> > +		}
> > +
> > +		i2c_put_dma_safe_msg_buf(req->buf, &msgs[i], true);
> > +	}
> > +
> > +	/*
> > +	 * Detach all the used buffers from the vq and
> > +	 * Release unused DMA safe buffer if any.
> > +	 */
> > +	for (j = i; j < nr; j++) {
> > +		req = virtqueue_get_buf(vq, &len);
> > +		if (req)
> > +			i2c_put_dma_safe_msg_buf(req->buf, &msgs[j], false);
> This will come in play only if something failed in the earlier loop ? Or my
> understanding incorrect ? Also this should be merged with the above for loop
> itself, it is just doing part of it.


Will refine it along with the earlier loop.


> > +	}
> > +
> > +	return i;
> > +}
> > +
> > +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);
> > +	virtqueue_kick(vq);
> > +
> > +	time_left = wait_for_completion_timeout(&vi->completion, adap->timeout);
> > +	if (!time_left) {
> On error here, we will surely not free the buffers, isn't it ?


Right. Will fix it. Thank you.


> > +		dev_err(&adap->dev, "virtio i2c backend timeout.\n");
> > +		ret = -ETIMEDOUT;
> > +		goto err_unlock_free;
> > +	}
> > +
> > +	ret = virtio_i2c_complete_reqs(vq, reqs, msgs, nr);
> > +
> > +err_unlock_free:
> > +	mutex_unlock(&vi->lock);
> > +	kfree(reqs);
> > +	return ret;
> > +}