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

From: Herve Codina <[email-masked]>
Date: Thu, 22 Feb 2024 17:45:01 +0100

On Thu, 22 Feb 2024 17:29:05 +0200
Andy Shevchenko <[email-masked]> wrote:

> 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?

These descriptors are not used by DMA.
Not sure that aligning them to a cacheline is really needed.

> 
> > +	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)
> 
> ?

Will be done in the next iteration.

> 
> ...
> 
> > +	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.

Will do that in the next iteration.

> 
> > +	}  
> 
> ...
> 
> > +	spin_lock_irqsave(&qmc_hdlc->tx_lock, flags);  
> 
> Why not using cleanup.h from day 1?

I don't know about cleanup.h.
Can you tell me more ?
How should I use it ?

> 
> > +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.

Sure, will be changed.

> 
> > +	}  
> 
> ...
> 
> > +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).

Will use that.

> 
> > +	struct device_node *np = pdev->dev.of_node;  
> 
> It is used only once, drop it (see below).

Ok.

> 
> > +	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...)

No reason. Just because I missed them.
Will be updated using dev_err_probe().

> 
> > +	}
> > +
> > +	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.

And I know :(
Will be updated.

> 
> > +	}
> > +
> > +	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;
> > +}  
> 
> 

Thanks for the review.

Hervé