Re: [PATCH v10] i2c: virtio: add a virtio i2c frontend driver

[Jie Deng]

On 2021/6/29 18:07, Wolfram Sang wrote:

> Hi,
>
> so some minor comments left:
>
> > +		if (!msgs[i].len)
> > +			break;
> I hope this can extended in the future to allow zero-length messages. If
> this is impossible we need to set an adapter quirk instead.


Yes, we can support it by removing this check and call it zero-length 
request.
It don't think it will break anything.


> > +		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);
> Is it really helpful for the user to know that msg5 failed? We don't
> even say which transfer.


OK. I will remove this print.


> > +static u32 virtio_i2c_func(struct i2c_adapter *adap)
> > +{
> > +	return I2C_FUNC_I2C | I2C_FUNC_SMBUS_EMUL;
> You are not emulating I2C_FUNC_SMBUS_QUICK, so you need to mask it out.


I will remove the check of  zero-length message.


> > +	snprintf(vi->adap.name, sizeof(vi->adap.name), "Virtio I2C Adapter");
> Is there something to add so you can distinguish multiple instances?
> Most people want that.


I find the I2C core will set a device name "i2c-%d" for this purpose, right?

I think this name can be used to distinguish the adapter types while 
"i2c-%d" can be used to

distinguish instances. Does it make sense ?


> > +	vi->adap.class = I2C_CLASS_DEPRECATED;
> > +	vi->adap.algo = &virtio_algorithm;
> > +	vi->adap.dev.parent = &vdev->dev;
> > +	vi->adap.timeout = HZ / 10;
> Why so short? HZ is the kinda default value.


Ah... I didn't know the I2C core had already set a default value.
I will remove this line to use the default one.


> > +	i2c_set_adapdata(&vi->adap, vi);
> > +
> > +	/* Setup ACPI node for controlled devices which will be probed through ACPI */
> > +	ACPI_COMPANION_SET(&vi->adap.dev, ACPI_COMPANION(pdev));
> > +
> > +	ret = i2c_add_adapter(&vi->adap);
> > +	if (ret) {
> > +		virtio_i2c_del_vqs(vdev);
> > +		dev_err(&vdev->dev, "failed to add virtio-i2c adapter.\n");
> Won't the driver core print that for us?


Yes. It seems unnecessary. Will remove it.


> > +	}
> > +
> > +	return ret;
> > +}
> > +
> > +/* The bit 0 of the @virtio_i2c_out_hdr.@flags, used to group the requests */
> > +#define VIRTIO_I2C_FLAGS_FAIL_NEXT	0x00000001
> BIT(0)?


That's better. Thank you.


> Happy hacking,
>
>     Wolfram