linux-kernel - Re: [PATCH v12] i2c: virtio: add a virtio i2c frontend driver

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Message-ID: <YN7jOm68fUL4UA2Q@smile.fi.intel.com>
Date:   Fri, 2 Jul 2021 12:58:18 +0300
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Jie Deng <jie.deng@...el.com>
Cc:     linux-i2c@...r.kernel.org,
        virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org, wsa@...nel.org,
        wsa+renesas@...g-engineering.com, mst@...hat.com, arnd@...db.de,
        jasowang@...hat.com, yu1.wang@...el.com, shuo.a.liu@...el.com,
        conghui.chen@...el.com, viresh.kumar@...aro.org,
        stefanha@...hat.com
Subject: Re: [PATCH v12] i2c: virtio: add a virtio i2c frontend driver

On Fri, Jul 02, 2021 at 04:46:47PM +0800, 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.

...

> +static int virtio_i2c_complete_reqs(struct virtqueue *vq,
> +				    struct virtio_i2c_req *reqs,
> +				    struct i2c_msg *msgs, int nr,
> +				    bool fail)
> +{
> +	struct virtio_i2c_req *req;
> +	bool failed = fail;
> +	unsigned int len;
> +	int i, j = 0;
> +
> +	for (i = 0; i < nr; i++) {
> +		/* Detach the ith request from the vq */
> +		req = virtqueue_get_buf(vq, &len);
> +
> +		/*
> +		 * Condition (req && req == &reqs[i]) should always meet since
> +		 * we have total nr requests in the vq.
> +		 */
> +		if (!failed && (WARN_ON(!(req && req == &reqs[i])) ||
> +		    (req->in_hdr.status != VIRTIO_I2C_MSG_OK)))
> +			failed = true;

...and after failed is true, we are continuing the loop, why?

> +		i2c_put_dma_safe_msg_buf(reqs[i].buf, &msgs[i], !failed);
> +		if (!failed)

> +			++j;

Besides better to read j++ the j itself can be renamed to something more
verbose.

> +	}

> +	return (fail ? -ETIMEDOUT : j);

Redundant parentheses.

> +}

...

> +	ret = virtio_i2c_send_reqs(vq, reqs, msgs, num);
> +	if (ret != num) {
> +		virtio_i2c_complete_reqs(vq, reqs, msgs, ret, true);

Below you check the returned code, here is not.

> +		ret = 0;
> +		goto err_free;
> +	}
> +
> +	reinit_completion(&vi->completion);
> +	virtqueue_kick(vq);
> +
> +	time_left = wait_for_completion_timeout(&vi->completion, adap->timeout);
> +	if (!time_left)
> +		dev_err(&adap->dev, "virtio i2c backend timeout.\n");
> +
> +	ret = virtio_i2c_complete_reqs(vq, reqs, msgs, num, !time_left);
> +
> +err_free:
> +	kfree(reqs);
> +	return ret;

> +++ b/include/uapi/linux/virtio_i2c.h

> +#include <linux/types.h>
> +
> +/* The bit 0 of the @virtio_i2c_out_hdr.@...gs, used to group the requests */
> +#define VIRTIO_I2C_FLAGS_FAIL_NEXT	BIT(0)

It's _BITUL() or so from linux/const.h.
https://elixir.bootlin.com/linux/latest/source/include/uapi/linux/const.h#L28
You may not use internal definitions in UAPI headers.

-- 
With Best Regards,
Andy Shevchenko