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

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

Hi,

so some minor comments left:

quoted

+		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.

quoted

+		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.

quoted

+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.

quoted

+	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 ?

quoted

+	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.

quoted

+	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.

quoted

+	}
+
+	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

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