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SubjectRe: [PATCH v14] i2c: virtio: add a virtio i2c frontend driver
On Fri, Jul 09, 2021 at 09:14:07AM +0530, Viresh Kumar wrote:
> On 09-07-21, 10:25, Jie Deng wrote:
> > Add an I2C bus driver for virtio para-virtualization.
> >
> > The controller can be emulated by the backend driver in
> > any device model software by following the virtio protocol.
> >
> > The device specification can be found on
> > https://lists.oasis-open.org/archives/virtio-comment/202101/msg00008.html.
> >
> > By following the specification, people may implement different
> > backend drivers to emulate different controllers according to
> > their needs.
> >
> > Co-developed-by: Conghui Chen <conghui.chen@intel.com>
> > Signed-off-by: Conghui Chen <conghui.chen@intel.com>
> > Signed-off-by: Jie Deng <jie.deng@intel.com>
> > ---
> > Changes v13 -> v14
> > - Put the headers in virtio_i2c.h in alphabetical order.
> > - Dropped I2C_FUNC_SMBUS_QUICK support.
> > - Dropped few unnecessary variables and checks.
> > - Use "num" everywhere instead of num or nr, to be consistent.
> > - Added few comments which make the design more clear.
>
> Thanks a lot for following this up so far :)
>
> > +static int virtio_i2c_prepare_reqs(struct virtqueue *vq,
> > + struct virtio_i2c_req *reqs,
> > + struct i2c_msg *msgs, int num)
> > +{
> > + struct scatterlist *sgs[3], out_hdr, msg_buf, in_hdr;
> > + int i;
> > +
> > + for (i = 0; i < num; i++) {
> > + int outcnt = 0, incnt = 0;
> > +
> > + /*
> > + * We don't support 0 length messages and so masked out
> > + * I2C_FUNC_SMBUS_QUICK in virtio_i2c_func().
> > + */
> > + 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 != num - 1)
> > + reqs[i].out_hdr.flags = cpu_to_le32(VIRTIO_I2C_FLAGS_FAIL_NEXT);
> > +
> > + 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);
> > + 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;
> > +
> > + if (virtqueue_add_sgs(vq, sgs, outcnt, incnt, &reqs[i], GFP_KERNEL)) {
> > + i2c_put_dma_safe_msg_buf(reqs[i].buf, &msgs[i], false);
> > + break;
> > + }
> > + }
> > +
> > + return i;
> > +}
>
> Wolfram, in case you wonder why we don't error out early as discussed earlier,
> then ...
>
> > +static int virtio_i2c_xfer(struct i2c_adapter *adap, struct i2c_msg *msgs,
> > + int num)
> > +{
>
> ...
>
> > + /*
> > + * For the case where count < num, i.e. we weren't able to queue all the
> > + * msgs, ideally we should abort right away and return early, but some
> > + * of the messages are already sent to the remote I2C controller and the
> > + * virtqueue will be left in undefined state in that case. We kick the
> > + * remote here to clear the virtqueue, so we can try another set of
> > + * messages later on.
> > + */
>
> ... here is the reasoning for that.
>
> Please see if you can still get it merged into 5.14-rc1/2. Thanks.
>
> Reviewed-by: Viresh Kumar <viresh.kumar@linaro.org>
> Tested-by: Viresh Kumar <viresh.kumar@linaro.org>

Well a new driver so maybe rc2 is still ok ...

Acked-by: Michael S. Tsirkin <mst@redhat.com>



> --
> viresh

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