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

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Date:   Wed, 30 Jun 2021 14:45:55 +0800
From:   Jie Deng <jie.deng@...el.com>
To:     Wolfram Sang <wsa@...nel.org>, linux-i2c@...r.kernel.org,
        virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org, mst@...hat.com, jasowang@...hat.com,
        andriy.shevchenko@...ux.intel.com, conghui.chen@...el.com,
        arnd@...db.de, kblaiech@...lanox.com,
        jarkko.nikula@...ux.intel.com, Sergey.Semin@...kalelectronics.ru,
        rppt@...nel.org, loic.poulain@...aro.org, tali.perry1@...il.com,
        u.kleine-koenig@...gutronix.de, bjorn.andersson@...aro.org,
        yu1.wang@...el.com, shuo.a.liu@...el.com, viresh.kumar@...aro.org,
        stefanha@...hat.com, pbonzini@...hat.com
Subject: 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:
>
>> +		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.@...gs, used to group the requests */
>> +#define VIRTIO_I2C_FLAGS_FAIL_NEXT	0x00000001
> BIT(0)?


That's better. Thank you.


>
> Happy hacking,
>
>     Wolfram
>