linux-kernel - Re: [PATCH v9] i2c: virtio: add a virtio i2c frontend driver

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Date:   Mon, 22 Mar 2021 12:11:44 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Jie Deng <jie.deng@...el.com>
Cc:     linux-i2c@...r.kernel.org,
        virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org, mst@...hat.com, wsa@...nel.org,
        jasowang@...hat.com, wsa+renesas@...g-engineering.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, stefanha@...hat.com,
        pbonzini@...hat.com
Subject: Re: [PATCH v9] i2c: virtio: add a virtio i2c frontend driver

On 22-03-21, 21:35, Jie Deng wrote:
> diff --git a/drivers/i2c/busses/i2c-virtio.c b/drivers/i2c/busses/i2c-virtio.c
> new file mode 100644
> index 0000000..316986e
> --- /dev/null
> +++ b/drivers/i2c/busses/i2c-virtio.c
> @@ -0,0 +1,286 @@
> +// SPDX-License-Identifier: GPL-2.0-or-later
> +/*
> + * Virtio I2C Bus Driver
> + *
> + * The Virtio I2C Specification:
> + * https://raw.githubusercontent.com/oasis-tcs/virtio-spec/master/virtio-i2c.tex
> + *
> + * Copyright (c) 2021 Intel Corporation. All rights reserved.
> + */
> +
> +#include <linux/acpi.h>
> +#include <linux/completion.h>
> +#include <linux/err.h>
> +#include <linux/i2c.h>
> +#include <linux/kernel.h>
> +#include <linux/module.h>
> +#include <linux/virtio.h>
> +#include <linux/virtio_ids.h>
> +#include <linux/virtio_config.h>
> +#include <linux/virtio_i2c.h>
> +
> +/**
> + * struct virtio_i2c - virtio I2C data
> + * @vdev: virtio device for this controller
> + * @completion: completion of virtio I2C message
> + * @adap: I2C adapter for this controller
> + * @i2c_lock: lock for virtqueue processing

Name mismatch here.

> + * @vq: the virtio virtqueue for communication
> + */
> +struct virtio_i2c {
> +	struct virtio_device *vdev;
> +	struct completion completion;
> +	struct i2c_adapter adap;
> +	struct mutex lock;
> +	struct virtqueue *vq;
> +};


> +static int virtio_i2c_complete_reqs(struct virtqueue *vq,
> +					struct virtio_i2c_req *reqs,
> +					struct i2c_msg *msgs, int nr,
> +					bool timeout)
> +{
> +	struct virtio_i2c_req *req;
> +	bool err_found = false;
> +	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);
> +
> +		if (timeout || err_found)  {
> +			i2c_put_dma_safe_msg_buf(reqs[i].buf, &msgs[i], false);
> +			continue;
> +		}
> +
> +		/*
> +		 * Condition (req && req == &reqs[i]) should always meet since
> +		 * we have total nr requests in the vq.
> +		 */
> +		if (WARN_ON(!(req && req == &reqs[i])) ||
> +		    (req->in_hdr.status != VIRTIO_I2C_MSG_OK)) {
> +			err_found = true;
> +			i2c_put_dma_safe_msg_buf(reqs[i].buf, &msgs[i], false);
> +			continue;
> +		}
> +
> +		i2c_put_dma_safe_msg_buf(reqs[i].buf, &msgs[i], true);
> +		++j;
> +	}

I think you can simplify the code like this here:

	bool err_found = timeout;

	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 (!err_found &&
                    (WARN_ON(!(req && req == &reqs[i])) ||
		     (req->in_hdr.status != VIRTIO_I2C_MSG_OK))) {
			err_found = true;
			continue;
		}

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

> +
> +	return (timeout ? -ETIMEDOUT : j);
> +}
> +
> +static int virtio_i2c_xfer(struct i2c_adapter *adap, struct i2c_msg *msgs, int num)
> +{
> +	struct virtio_i2c *vi = i2c_get_adapdata(adap);
> +	struct virtqueue *vq = vi->vq;
> +	struct virtio_i2c_req *reqs;
> +	unsigned long time_left;
> +	int ret, nr;
> +
> +	reqs = kcalloc(num, sizeof(*reqs), GFP_KERNEL);
> +	if (!reqs)
> +		return -ENOMEM;
> +
> +	mutex_lock(&vi->lock);
> +
> +	ret = virtio_i2c_send_reqs(vq, reqs, msgs, num);
> +	if (ret == 0)
> +		goto err_unlock_free;
> +
> +	nr = ret;
> +	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, nr, true);
> +		goto err_unlock_free;
> +	}
> +
> +	ret = virtio_i2c_complete_reqs(vq, reqs, msgs, nr, false);

And this can be optimized as well:

	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, nr, !time_left);

-- 
viresh