On 2021/7/1 14:18, Viresh Kumar wrote:

On 01-07-21, 14:10, Jie Deng wrote:

quoted

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;
+}


_______________________________________________
Virtualization mailing list
Virtualization@lists.linux-foundation.org
https://lists.linuxfoundation.org/mailman/listinfo/virtualization