Date: Thu, 12 Oct 2023 13:50:39 +0200
From: Paolo Abeni <pabeni@...hat.com>
To: Matt Johnston <matt@...econstruct.com.au>,
 linux-i3c@...ts.infradead.org,  netdev@...r.kernel.org,
 devicetree@...r.kernel.org
Cc: "David S. Miller" <davem@...emloft.net>, Jakub Kicinski
 <kuba@...nel.org>,  Eric Dumazet <edumazet@...gle.com>, Jeremy Kerr
 <jk@...econstruct.com.au>, Alexandre Belloni
 <alexandre.belloni@...tlin.com>, Rob Herring <robh+dt@...nel.org>,
 Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>, Conor Dooley
 <conor+dt@...nel.org>,  miquel.raynal@...tlin.com
Subject: Re: [PATCH net-next v5 3/3] mctp i3c: MCTP I3C driver

On Mon, 2023-10-09 at 10:54 +0800, Matt Johnston wrote:

> +static int mctp_i3c_setup(struct mctp_i3c_device *mi)
> +{
> +	bool ibi_set = false, ibi_enabled = false;
> +	const struct i3c_ibi_setup ibi = {
> +		.max_payload_len = 1,
> +		.num_slots = MCTP_I3C_IBI_SLOTS,
> +		.handler = mctp_i3c_ibi_handler,
> +	};
> +	struct i3c_device_info info;
> +	int rc;
> +
> +	i3c_device_get_info(mi->i3c, &info);
> +	mi->have_mdb = info.bcr & BIT(2);
> +	mi->addr = info.dyn_addr;
> +	mi->mwl = info.max_write_len;
> +	mi->mrl = info.max_read_len;
> +	mi->pid = info.pid;
> +
> +	rc = i3c_device_request_ibi(mi->i3c, &ibi);
> +	if (rc == 0) {
> +		ibi_set = true;
> +	} else if (rc == -ENOTSUPP) {
> +		/* This driver only supports In-Band Interrupt mode
> +		 * (ENOTSUPP is from the i3c layer, not EOPNOTSUPP).
> +		 * Support for Polling Mode could be added if required.
> +		 */
> +		dev_warn(i3cdev_to_dev(mi->i3c), "Failed, bus driver doesn't support In-Band Interrupts");
> +		goto err;
> +	} else {
> +		dev_err(i3cdev_to_dev(mi->i3c),
> +			"Failed requesting IBI (%d)\n", rc);
> +		goto err;
> +	}
> +
> +	if (ibi_set) {
> +		/* Device setup must be complete when IBI is enabled */
> +		rc = i3c_device_enable_ibi(mi->i3c);
> +		if (rc < 0) {
> +			/* Assume a driver supporting request_ibi also
> +			 * supports enable_ibi.
> +			 */
> +			dev_err(i3cdev_to_dev(mi->i3c),
> +				"Failed enabling IBI (%d)\n", rc);
> +			goto err;
> +		}
> +		ibi_enabled = true;
> +	}
> +
> +	return 0;
> +err:
> +	if (ibi_enabled)
> +		i3c_device_disable_ibi(mi->i3c);

Apparently no error code path can reach here with 'ibi_enabled ==
true', if so please drop the above lines.

> +	if (ibi_set)
> +		i3c_device_free_ibi(mi->i3c);
> +	return rc;
> +}
> +
> +/* Adds a new MCTP i3c_device to a bus */
> +static int mctp_i3c_add_device(struct mctp_i3c_bus *mbus,
> +			       struct i3c_device *i3c)
> +__must_hold(&busdevs_lock)
> +{
> +	struct mctp_i3c_device *mi = NULL;
> +	int rc;
> +
> +	mi = kzalloc(sizeof(*mi), GFP_KERNEL);
> +	if (!mi) {
> +		rc = -ENOMEM;
> +		goto err;
> +	}
> +	mi->mbus = mbus;
> +	mi->i3c = i3c;
> +	mutex_init(&mi->lock);
> +	list_add(&mi->list, &mbus->devs);
> +
> +	i3cdev_set_drvdata(i3c, mi);
> +	rc = mctp_i3c_setup(mi);
> +	if (rc < 0)
> +		goto err;

You can make the code simpler with:

		goto free;
> +
> +	return 0;

and here:

free:
	list_del(&mi->list);
	kfree(mi);

err:
	dev_warn(i3cdev_to_dev(i3c), "Error adding mctp-i3c device, %d\n", rc);
	return rc;

> +err:
> +	dev_warn(i3cdev_to_dev(i3c), "Error adding mctp-i3c device, %d\n", rc);
> +	if (mi) {
> +		list_del(&mi->list);
> +		kfree(mi);
> +	}
> +	return rc;
> +}
> +
> +static int mctp_i3c_probe(struct i3c_device *i3c)
> +{
> +	struct mctp_i3c_bus *b = NULL, *mbus = NULL;
> +	int rc;
> +
> +	/* Look for a known bus */
> +	mutex_lock(&busdevs_lock);
> +	list_for_each_entry(b, &busdevs, list)
> +		if (b->bus == i3c->bus) {
> +			mbus = b;
> +			break;
> +		}
> +	mutex_unlock(&busdevs_lock);
> +
> +	if (!mbus) {
> +		/* probably no "mctp-controller" property on the i3c bus */
> +		return -ENODEV;
> +	}
> +
> +	rc = mctp_i3c_add_device(mbus, i3c);
> +	if (!rc)
> +		goto err;

This is confusing: if 'rc' is zero (!rc) the function will return 0
('return rc' later), and otherwise it will return zero again.

Either ignore the return code, or more likely the error path need some
change.

> +static void mctp_i3c_xmit(struct mctp_i3c_bus *mbus, struct sk_buff *skb)
> +{
> +	struct net_device_stats *stats = &mbus->ndev->stats;
> +	struct i3c_priv_xfer xfer = { .rnw = false };
> +	struct mctp_i3c_internal_hdr *ihdr = NULL;
> +	struct mctp_i3c_device *mi = NULL;
> +	unsigned int data_len;
> +	u8 *data = NULL;
> +	u8 addr, pec;
> +	int rc = 0;
> +	u64 pid;
> +
> +	skb_pull(skb, sizeof(struct mctp_i3c_internal_hdr));
> +	data_len = skb->len;
> +
> +	ihdr = (void *)skb_mac_header(skb);
> +
> +	pid = get_unaligned_be48(ihdr->dest);
> +	mi = mctp_i3c_lookup(mbus, pid);
> +	if (!mi) {
> +		/* I3C endpoint went away after the packet was enqueued? */
> +		stats->tx_dropped++;
> +		goto out;
> +	}
> +
> +	if (WARN_ON_ONCE(data_len + 1 > MCTP_I3C_MAXBUF))
> +		goto out;
> +
> +	if (data_len + 1 > (unsigned int)mi->mwl) {
> +		/* Route MTU was larger than supported by the endpoint */
> +		stats->tx_dropped++;
> +		goto out;
> +	}
> +
> +	/* Need a linear buffer with space for the PEC */
> +	xfer.len = data_len + 1;
> +	if (skb_tailroom(skb) >= 1) {
> +		skb_put(skb, 1);
> +		data = skb->data;
> +	} else {
> +		// TODO: test this

I hope this comment is a left over? In any case please avoid c++ style
comments.

> +		/* Otherwise need to copy the buffer */
> +		skb_copy_bits(skb, 0, mbus->tx_scratch, skb->len);
> +		data = mbus->tx_scratch;
> +	}
> +
> +	/* PEC calculation */
> +	addr = mi->addr << 1;
> +	pec = i2c_smbus_pec(0, &addr, 1);
> +	pec = i2c_smbus_pec(pec, data, data_len);
> +	data[data_len] = pec;
> +
> +	xfer.data.out = data;
> +	rc = i3c_device_do_priv_xfers(mi->i3c, &xfer, 1);
> +	if (rc == 0) {
> +		stats->tx_bytes += data_len;
> +		stats->tx_packets++;
> +	} else {
> +		stats->tx_errors++;
> +	}
> +
> +out:
> +	if (mi)
> +		mutex_unlock(&mi->lock);
> +}
> +
> +static int mctp_i3c_tx_thread(void *data)
> +{
> +	struct mctp_i3c_bus *mbus = data;
> +	struct sk_buff *skb;
> +	unsigned long flags;
> +
> +	for (;;) {
> +		if (kthread_should_stop())
> +			break;
> +
> +		spin_lock_irqsave(&mbus->tx_lock, flags);
> +		skb = mbus->tx_skb;
> +		mbus->tx_skb = NULL;
> +		spin_unlock_irqrestore(&mbus->tx_lock, flags);
> +
> +		if (netif_queue_stopped(mbus->ndev))
> +			netif_wake_queue(mbus->ndev);
> +
> +		if (skb) {
> +			mctp_i3c_xmit(mbus, skb);
> +			kfree_skb(skb);
> +		} else {
> +			wait_event_idle(mbus->tx_wq,
> +					mbus->tx_skb || kthread_should_stop());
> +		}
> +	}
> +
> +	return 0;
> +}
> +
> +static netdev_tx_t mctp_i3c_start_xmit(struct sk_buff *skb,
> +				       struct net_device *ndev)
> +{
> +	struct mctp_i3c_bus *mbus = netdev_priv(ndev);
> +	unsigned long flags;
> +	netdev_tx_t ret;
> +
> +	spin_lock_irqsave(&mbus->tx_lock, flags);

Why are you using the _irqsave variant? The only other path acquiring
this lock is mctp_i3c_tx_thread(), in process context, while here we
have BH disabled. Plain spin_lock should suffice here, paired with _BH
variant in mctp_i3c_tx_thread.

> +	netif_stop_queue(ndev);
> +	if (mbus->tx_skb) {
> +		dev_warn_ratelimited(&ndev->dev, "TX with queue stopped");
> +		ret = NETDEV_TX_BUSY;
> +	} else {
> +		mbus->tx_skb = skb;
> +		ret = NETDEV_TX_OK;
> +	}
> +	spin_unlock_irqrestore(&mbus->tx_lock, flags);
> +
> +	if (ret == NETDEV_TX_OK)
> +		wake_up(&mbus->tx_wq);
> +
> +	return ret;
> +}

[...]

> +/* Returns an ERR_PTR on failure */
> +static struct mctp_i3c_bus *mctp_i3c_bus_add(struct i3c_bus *bus)
> +__must_hold(&busdevs_lock)
> +{
> +	struct mctp_i3c_bus *mbus = NULL;
> +	struct net_device *ndev = NULL;
> +	char namebuf[IFNAMSIZ];
> +	u8 addr[PID_SIZE];
> +	int rc;
> +
> +	if (!mctp_i3c_is_mctp_controller(bus))
> +		return ERR_PTR(-ENOENT);
> +
> +	snprintf(namebuf, sizeof(namebuf), "mctpi3c%d", bus->id);
> +	ndev = alloc_netdev(sizeof(*mbus), namebuf, NET_NAME_ENUM,
> +			    mctp_i3c_net_setup);
> +	if (!ndev) {
> +		rc = -ENOMEM;
> +		goto err;
> +	}
> +
> +	mbus = netdev_priv(ndev);
> +	mbus->ndev = ndev;
> +	mbus->bus = bus;
> +	INIT_LIST_HEAD(&mbus->devs);
> +	list_add(&mbus->list, &busdevs);
> +
> +	rc = mctp_i3c_bus_local_pid(bus, &mbus->pid);
> +	if (rc < 0) {
> +		dev_err(&ndev->dev, "No I3C PID available\n");
> +		goto err;
> +	}
> +	put_unaligned_be48(mbus->pid, addr);
> +	dev_addr_set(ndev, addr);
> +
> +	init_waitqueue_head(&mbus->tx_wq);
> +	spin_lock_init(&mbus->tx_lock);
> +	mbus->tx_thread = kthread_run(mctp_i3c_tx_thread, mbus,
> +				      "%s/tx", ndev->name);
> +	if (IS_ERR(mbus->tx_thread)) {
> +		dev_warn(&ndev->dev, "Error creating thread: %pe\n",
> +			 mbus->tx_thread);
> +		rc = PTR_ERR(mbus->tx_thread);
> +		mbus->tx_thread = NULL;
> +		goto err;
> +	}
> +
> +	rc = mctp_register_netdev(ndev, NULL);
> +	if (rc < 0) {
> +		dev_warn(&ndev->dev, "netdev register failed: %d\n", rc);
> +		goto err;
> +	}
> +	return mbus;
> +err:
> +	/* uninit will not get called if a netdev has not been registered,
> +	 * so we perform the same mbus cleanup manually.
> +	 */
> +	if (mbus)
> +		mctp_i3c_bus_free(mbus);
> +	if (ndev)
> +		free_netdev(ndev);

A more conventional way of handling the error paths would be using
multiple labels, e.g.:

err_free_bus:
	mctp_i3c_bus_free(mbus);

err_free_ndev:
	free_netdev(ndev);

err:

> +	return ERR_PTR(rc);
> +}

Cheers,

Paolo

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