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

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Date:   Fri, 19 Mar 2021 15:52:05 +0800
From:   Jie Deng <jie.deng@...el.com>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     linux-i2c@...r.kernel.org,
        virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org, mst@...hat.com, wsa@...nel.org,
        jasowang@...hat.com, wsa+renesas@...g-engineering.com,
        andriy.shevchenko@...ux.intel.com, conghui.chen@...el.com,
        arnd@...db.de, kblaiech@...lanox.com,
        jarkko.nikula@...ux.intel.com, Sergey.Semin@...kalelectronics.ru,
        rppt@...nel.org, loic.poulain@...aro.org, tali.perry1@...il.com,
        u.kleine-koenig@...gutronix.de, bjorn.andersson@...aro.org,
        yu1.wang@...el.com, shuo.a.liu@...el.com, stefanha@...hat.com,
        pbonzini@...hat.com
Subject: Re: [PATCH v8] i2c: virtio: add a virtio i2c frontend driver


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;
>> +}