Re: [PATCH v5] i2c: virtio: add a virtio i2c frontend driver

Viresh Kumar
2021-03-03T13:06:33Z

On 01-03-21, 14:41, Jie Deng wrote:
> diff --git a/drivers/i2c/busses/i2c-virtio.c 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;
> + u8 *buf;
> +
> + for (i = 0; i < nr; i++) {
> + if (!msgs[i].len)
> + break;
> +
> + reqs[i].out_hdr.addr = cpu_to_le16(msgs[i].addr << 1);
> +
> + if (i != nr - 1)
> + reqs[i].out_hdr.flags |= 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;
> +
> + buf = kzalloc(msgs[i].len, GFP_KERNEL);
> + if (!buf)
> + break;
> +
> + if (msgs[i].flags & I2C_M_RD) {
> + reqs[i].read_buf = buf;
> + sg_init_one(&msg_buf, reqs[i].read_buf, msgs[i].len);
> + sgs[outcnt + incnt++] = &msg_buf;
> + } else {
> + reqs[i].write_buf = buf;
> + memcpy(reqs[i].write_buf, msgs[i].buf, msgs[i].len);
> + sg_init_one(&msg_buf, reqs[i].write_buf, msgs[i].len);
> + 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);
> + if (msgs[i].flags & I2C_M_RD) {
> + kfree(reqs[i].read_buf);
> + reqs[i].read_buf = NULL;
> + } else {
> + kfree(reqs[i].write_buf);
> + reqs[i].write_buf = NULL;
> + }
> + break;
> + }
> + }
> +
> + return i;
> +}

> diff --git a/include/uapi/linux/virtio_i2c.h b/include/uapi/linux/virtio_i2c.h
> +/**
> + * struct virtio_i2c_out_hdr - the virtio I2C message OUT header
> + * @addr: the controlled device address
> + * @padding: used to pad to full dword
> + * @flags: used for feature extensibility
> + */
> +struct virtio_i2c_out_hdr {
> + __le16 addr;
> + __le16 padding;
> + __le32 flags;
> +};

Both this code and the virtio spec (which is already merged) are
missing msgs[i].flags and they are never sent to backend. The only
flags available here are the ones defined by virtio spec and these are
not i2c flags.

I also looked at your i2c backend for acrn and it mistakenly copies
the hdr.flag, which is the virtio flag and not i2c flag.

https://github.com/projectacrn/acrn-hypervisor/blob/master/devicemodel/hw/pci/virtio/virtio_i2c.c#L539

I will send a fix for the specs if you agree that there is a problem
here.

what am I missing here ? This should have been caught in your testing
and so I feel I must be missing something.

--
viresh