netdev - Re: [PATCH v4 1/5] net: wan: Add support for QMC HDLC

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Message-ID: <ZddoQTg32unJJ_qP@smile.fi.intel.com>
Date: Thu, 22 Feb 2024 17:29:05 +0200
From: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To: Herve Codina <herve.codina@...tlin.com>
Cc: Vadim Fedorenko <vadim.fedorenko@...ux.dev>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Yury Norov <yury.norov@...il.com>,
	Rasmus Villemoes <linux@...musvillemoes.dk>,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	linuxppc-dev@...ts.ozlabs.org, Andrew Lunn <andrew@...n.ch>,
	Mark Brown <broonie@...nel.org>,
	Christophe Leroy <christophe.leroy@...roup.eu>,
	Thomas Petazzoni <thomas.petazzoni@...tlin.com>
Subject: Re: [PATCH v4 1/5] net: wan: Add support for QMC HDLC

On Thu, Feb 22, 2024 at 03:22:14PM +0100, Herve Codina wrote:
> The QMC HDLC driver provides support for HDLC using the QMC (QUICC
> Multichannel Controller) to transfer the HDLC data.

...

> +struct qmc_hdlc {
> +	struct device *dev;
> +	struct qmc_chan *qmc_chan;
> +	struct net_device *netdev;
> +	bool is_crc32;
> +	spinlock_t tx_lock; /* Protect tx descriptors */

Just wondering if above tx/rx descriptors should be aligned on a cacheline
for DMA?

> +	struct qmc_hdlc_desc tx_descs[8];
> +	unsigned int tx_out;
> +	struct qmc_hdlc_desc rx_descs[4];
> +};

...

> +#define QMC_HDLC_RX_ERROR_FLAGS (QMC_RX_FLAG_HDLC_OVF | \
> +				 QMC_RX_FLAG_HDLC_UNA | \
> +				 QMC_RX_FLAG_HDLC_ABORT | \
> +				 QMC_RX_FLAG_HDLC_CRC)

Wouldn't be slightly better to have it as

#define QMC_HDLC_RX_ERROR_FLAGS				\
	(QMC_RX_FLAG_HDLC_OVF | QMC_RX_FLAG_HDLC_UNA |	\
	 QMC_RX_FLAG_HDLC_CRC | QMC_RX_FLAG_HDLC_ABORT)

?

...

> +	ret = qmc_chan_write_submit(qmc_hdlc->qmc_chan, desc->dma_addr, desc->dma_size,
> +				    qmc_hdlc_xmit_complete, desc);
> +	if (ret) {

> +		dev_err(qmc_hdlc->dev, "qmc chan write returns %d\n", ret);
> +		dma_unmap_single(qmc_hdlc->dev, desc->dma_addr, desc->dma_size, DMA_TO_DEVICE);
> +		return ret;

I would do other way around, i.e. release resource followed up by printing
a message. Printing a message is a slow operation and may prevent the (soon
freed) resources to be re-used earlier.

> +	}

...

> +	spin_lock_irqsave(&qmc_hdlc->tx_lock, flags);

Why not using cleanup.h from day 1?

> +end:

This label, in particular, will not be needed with above in place.

> +	spin_unlock_irqrestore(&qmc_hdlc->tx_lock, flags);
> +	return ret;
> +}

...

> +	/* Queue as many recv descriptors as possible */
> +	for (i = 0; i < ARRAY_SIZE(qmc_hdlc->rx_descs); i++) {
> +		desc = &qmc_hdlc->rx_descs[i];
> +
> +		desc->netdev = netdev;
> +		ret = qmc_hdlc_recv_queue(qmc_hdlc, desc, chan_param.hdlc.max_rx_buf_size);

> +		if (ret) {
> +			if (ret == -EBUSY && i != 0)
> +				break; /* We use all the QMC chan capability */
> +			goto free_desc;
> +		}

Can be unfolded to

		if (ret == -EBUSY && i)
			break; /* We use all the QMC chan capability */
		if (ret)
			goto free_desc;

Easy to read and understand.

> +	}

...

> +static int qmc_hdlc_probe(struct platform_device *pdev)
> +{

With

	struct device *dev = &pdev->dev;

the below code will be neater (see other comments for the examples).

> +	struct device_node *np = pdev->dev.of_node;

It is used only once, drop it (see below).

> +	struct qmc_hdlc *qmc_hdlc;
> +	struct qmc_chan_info info;
> +	hdlc_device *hdlc;
> +	int ret;
> +
> +	qmc_hdlc = devm_kzalloc(&pdev->dev, sizeof(*qmc_hdlc), GFP_KERNEL);
> +	if (!qmc_hdlc)
> +		return -ENOMEM;
> +
> +	qmc_hdlc->dev = &pdev->dev;
> +	spin_lock_init(&qmc_hdlc->tx_lock);
> +
> +	qmc_hdlc->qmc_chan = devm_qmc_chan_get_bychild(qmc_hdlc->dev, np);

	qmc_hdlc->qmc_chan = devm_qmc_chan_get_bychild(dev, dev->of_node);

> +	if (IS_ERR(qmc_hdlc->qmc_chan)) {
> +		ret = PTR_ERR(qmc_hdlc->qmc_chan);
> +		return dev_err_probe(qmc_hdlc->dev, ret, "get QMC channel failed\n");

		return dev_err_probe(dev, PTR_ERR(qmc_hdlc->qmc_chan), "get QMC channel failed\n");

> +	}
> +
> +	ret = qmc_chan_get_info(qmc_hdlc->qmc_chan, &info);
> +	if (ret) {

> +		dev_err(qmc_hdlc->dev, "get QMC channel info failed %d\n", ret);
> +		return ret;

Why not using same message pattern everywhere, i.e. dev_err_probe()?

		return dev_err_probe(dev, ret, "get QMC channel info failed\n");

(and so on...)

> +	}
> +
> +	if (info.mode != QMC_HDLC) {
> +		dev_err(qmc_hdlc->dev, "QMC chan mode %d is not QMC_HDLC\n",
> +			info.mode);
> +		return -EINVAL;
> +	}
> +
> +	qmc_hdlc->netdev = alloc_hdlcdev(qmc_hdlc);
> +	if (!qmc_hdlc->netdev) {

> +		dev_err(qmc_hdlc->dev, "failed to alloc hdlc dev\n");
> +		return -ENOMEM;

We do not issue a message for -ENOMEM.

> +	}
> +
> +	hdlc = dev_to_hdlc(qmc_hdlc->netdev);
> +	hdlc->attach = qmc_hdlc_attach;
> +	hdlc->xmit = qmc_hdlc_xmit;
> +	SET_NETDEV_DEV(qmc_hdlc->netdev, qmc_hdlc->dev);
> +	qmc_hdlc->netdev->tx_queue_len = ARRAY_SIZE(qmc_hdlc->tx_descs);
> +	qmc_hdlc->netdev->netdev_ops = &qmc_hdlc_netdev_ops;
> +	ret = register_hdlc_device(qmc_hdlc->netdev);
> +	if (ret) {
> +		dev_err(qmc_hdlc->dev, "failed to register hdlc device (%d)\n", ret);
> +		goto free_netdev;
> +	}
> +
> +	platform_set_drvdata(pdev, qmc_hdlc);
> +
> +	return 0;
> +
> +free_netdev:
> +	free_netdev(qmc_hdlc->netdev);
> +	return ret;
> +}


-- 
With Best Regards,
Andy Shevchenko