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Message-ID: <3dc0d61c-9345-2b61-828c-89ca96555e5e@redhat.com>
Date: Mon, 7 Sep 2020 13:40:20 +0800
From: Jason Wang <jasowang@...hat.com>
To: Jie Deng <jie.deng@...el.com>, linux-i2c@...r.kernel.org,
virtualization@...ts.linux-foundation.org,
linux-kernel@...r.kernel.org
Cc: mst@...hat.com, wsa+renesas@...g-engineering.com, wsa@...nel.org,
andriy.shevchenko@...ux.intel.com, jarkko.nikula@...ux.intel.com,
jdelvare@...e.de, Sergey.Semin@...kalelectronics.ru,
krzk@...nel.org, rppt@...nel.org, loic.poulain@...aro.org,
tali.perry1@...il.com, bjorn.andersson@...aro.org,
shuo.a.liu@...el.com, conghui.chen@...el.com, yu1.wang@...el.com
Subject: Re: [PATCH] i2c: virtio: add a virtio i2c frontend driver
On 2020/9/4 下午9:21, Jie Deng wrote:
>
> On 2020/9/4 12:06, Jason Wang wrote:
>>
>>> diff --git a/drivers/i2c/busses/Kconfig b/drivers/i2c/busses/Kconfig
>>> index 293e7a0..70c8e30 100644
>>> --- a/drivers/i2c/busses/Kconfig
>>> +++ b/drivers/i2c/busses/Kconfig
>>> @@ -21,6 +21,17 @@ config I2C_ALI1535
>>> This driver can also be built as a module. If so, the module
>>> will be called i2c-ali1535.
>>> +config I2C_VIRTIO
>>> + tristate "Virtio I2C Adapter"
>>> + depends on VIRTIO
>>
>>
>> I guess it should depend on some I2C module here.
>>
> The dependency of I2C is included in the Kconfig in its parent directory.
> So there is nothing special to add here.
Ok.
>
>
>>
>>>
>>> +struct virtio_i2c_msg {
>>> + struct virtio_i2c_hdr hdr;
>>> + char *buf;
>>> + u8 status;
>>
>>
>> Any reason for separating status out of virtio_i2c_hdr?
>>
> The status is not from i2c_msg.
You meant ic2_hdr? You embed status in virtio_i2c_msg anyway.
> So I put it out of virtio_i2c_hdr.
Something like status or response is pretty common in virtio request
(e.g net or scsi), if no special reason, it's better to keep it in the hdr.
>
>>
>>> +};
>>> +
>>> +/**
>>> + * struct virtio_i2c - virtio I2C data
>>> + * @vdev: virtio device for this controller
>>> + * @completion: completion of virtio I2C message
>>> + * @adap: I2C adapter for this controller
>>> + * @i2c_lock: lock for virtqueue processing
>>> + * @vq: the virtio virtqueue for communication
>>> + */
>>> +struct virtio_i2c {
>>> + struct virtio_device *vdev;
>>> + struct completion completion;
>>> + struct i2c_adapter adap;
>>> + struct mutex i2c_lock;
>>> + struct virtqueue *vq;
>>> +};
>>> +
>>> +static void virtio_i2c_msg_done(struct virtqueue *vq)
>>> +{
>>> + struct virtio_i2c *vi = vq->vdev->priv;
>>> +
>>> + complete(&vi->completion);
>>> +}
>>> +
>>> +static int virtio_i2c_add_msg(struct virtqueue *vq,
>>> + struct virtio_i2c_msg *vmsg,
>>> + struct i2c_msg *msg)
>>> +{
>>> + struct scatterlist *sgs[3], hdr, bout, bin, status;
>>> + int outcnt = 0, incnt = 0;
>>> +
>>> + if (!msg->len)
>>> + return -EINVAL;
>>> +
>>> + vmsg->hdr.addr = msg->addr;
>>> + vmsg->hdr.flags = msg->flags;
>>> + vmsg->hdr.len = msg->len;
>>
>>
>> Missing endian conversion?
>>
> You are right. Need conversion here.
>>
>>> +
>>> + vmsg->buf = kzalloc(vmsg->hdr.len, GFP_KERNEL);
>>> + if (!vmsg->buf)
>>> + return -ENOMEM;
>>> +
>>> + sg_init_one(&hdr, &vmsg->hdr, sizeof(struct virtio_i2c_hdr));
>>> + sgs[outcnt++] = &hdr;
>>> + if (vmsg->hdr.flags & I2C_M_RD) {
>>> + sg_init_one(&bin, vmsg->buf, msg->len);
>>> + sgs[outcnt + incnt++] = &bin;
>>> + } else {
>>> + memcpy(vmsg->buf, msg->buf, msg->len);
>>> + sg_init_one(&bout, vmsg->buf, msg->len);
>>> + sgs[outcnt++] = &bout;
>>> + }
>>> + sg_init_one(&status, &vmsg->status, sizeof(vmsg->status));
>>> + sgs[outcnt + incnt++] = &status;
>>> +
>>> + return virtqueue_add_sgs(vq, sgs, outcnt, incnt, vmsg,
>>> GFP_KERNEL);
>>> +}
>>> +
>>> +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;
>>
>>
>> It looks to me we can avoid the allocation by embedding
>> virtio_i2c_msg into struct virtio_i2c;
>>
> Yeah... That's better. Thanks.
>
>
>>
>>> +
>>> + 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;
>>> + }
>>> +
>>> + 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;
>>> + }
>>> +
>>> + 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;
>>> + }
>>
>>
>> Does this imply in order completion of i2c device? (E.g what happens
>> if multiple virtio i2c requests are submitted)
>>
>> Btw, this always use a single descriptor once a time which makes me
>> suspect if a virtqueue(virtio) is really needed. It looks to me we
>> can utilize the virtqueue by submit the request in a batch.
>>
> I'm afraid not all physical devices support batch.
Yes but I think I meant for the virtio device not the physical one. It's
impossible to forbid batching if you have a queue anyway ...
> I'd like to keep the current design and consider
> your suggestion as a possible optimization in the future.
>
> Thanks.
>
>
>>>
>>> +}
>>> +
>>> +static void virtio_i2c_del_vqs(struct virtio_device *vdev)
>>> +{
>>> + vdev->config->reset(vdev);
>>
>>
>> Why need reset here?
>>
>> Thanks
>>
> I'm following what other virtio drivers do.
> They reset the devices before they clean up the queues.
You're ring.
Thanks
>
>
>>
>>> + vdev->config->del_vqs(vdev);
>>> +}
>>> +
>>> +static int virtio_i2c_setup_vqs(struct virtio_i2c *vi)
>>> +{
>>> + struct virtio_device *vdev = vi->vdev;
>>> +
>>> + vi->vq = virtio_find_single_vq(vdev, virtio_i2c_msg_done,
>>> "i2c-msg");
>>
>>
>> We've in the scope of ic2, so "msg" should be sufficient.
>>
>>
> OK. Will change this name. Thanks.
>
>
>>> + return PTR_ERR_OR_ZERO(vi->vq);
>
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