Re: [PATCH v11] i2c: virtio: add a virtio i2c frontend driver

[Jie Deng]

On 2021/7/1 14:18, Viresh Kumar wrote:
> On 01-07-21, 14:10, Jie Deng wrote:
> > I think a fixed number of sgs will make things easier to develop backend.
> Yeah, but it looks awkward to send a message buffer which isn't used
> at all. From protocol's point of view, it just looks wrong/buggy.
>
> The backend can just look at the number of elements received, they
> can either be 2 (in case of zero-length) transfer, or 3 (for
> read/write) and any other number is invalid.

OK. Let's add the following two lines to make sure that msg_buf is only
sent when the msgs len is not zero. And backend judges whether it is
a zero-length request by checking the number of elements received.

 + if (msgs[i].len) {
           reqs[i].buf = i2c_get_dma_safe_msg_buf(&msgs[i], 1);
           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;
+}