netdev - Re: [PATCH V3 net-next 2/2] net: broadcom: bcm4908

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Date:   Wed, 10 Feb 2021 08:57:50 +0100
From:   Rafał Miłecki <rafal@...ecki.pl>
To:     Andrew Lunn <andrew@...n.ch>,
        Rafał Miłecki <zajec5@...il.com>
Cc:     "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Florian Fainelli <f.fainelli@...il.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Masahiro Yamada <masahiroy@...nel.org>, netdev@...r.kernel.org,
        devicetree@...r.kernel.org, bcm-kernel-feedback-list@...adcom.com
Subject: Re: [PATCH V3 net-next 2/2] net: broadcom: bcm4908_enet: add BCM4908
 controller driver

On 10.02.2021 03:39, Andrew Lunn wrote:
>> +static inline u32 enet_read(struct bcm4908_enet *enet, u16 offset)
>> +{
>> +	return readl(enet->base + offset);
>> +}
> 
> No inline functions in C files please. Let the compiler decide.

According to the kernel's coding style (coding-style.rst) inline should
*not* be used for 3+ LOC functions in general. According to that, I should
only fix my enet_maskset() which isn't 1 LOC indeed.

If that Documentation is outdated and/or inaccurate, could you propose a
change for it, please? That rule comes from 2006 (a771f2b82aa2), so I
understand it may need updating. We should have that officially documented
though, to avoid per-tree or per-maintainer rules for stuff like this.

Personally I don't have enough compiler knowledge to propose and/or discuss
such stuff. That's why I prefer following Documentation written by smarter
ones ;)


>> +static int bcm4908_dma_alloc_buf_descs(struct bcm4908_enet *enet,
>> +				       struct bcm4908_enet_dma_ring *ring)
>> +{
>> +	int size = ring->length * sizeof(struct bcm4908_enet_dma_ring_bd);
>> +	struct device *dev = enet->dev;
>> +
>> +	ring->cpu_addr = dma_alloc_coherent(dev, size, &ring->dma_addr, GFP_KERNEL);
>> +	if (!ring->cpu_addr)
>> +		return -ENOMEM;
>> +
>> +	if (((uintptr_t)ring->cpu_addr) & (0x40 - 1)) {
>> +		dev_err(dev, "Invalid DMA ring alignment\n");
>> +		goto err_free_buf_descs;
>> +	}
>> +
>> +	ring->slots = kzalloc(ring->length * sizeof(*ring->slots), GFP_KERNEL);
>> +	if (!ring->slots)
>> +		goto err_free_buf_descs;
>> +
>> +	memset(ring->cpu_addr, 0, size);
> 
> It looks like dma_alloc_coherent() will perform a clear. See __dma_alloc_from_coherent()

Thanks!


>> +static void bcm4908_enet_dma_reset(struct bcm4908_enet *enet)
>> +{
>> +	struct bcm4908_enet_dma_ring *rings[] = { &enet->rx_ring, &enet->tx_ring };
>> +	int i;
>> +
>> +	/* Disable the DMA controller and channel */
>> +	for (i = 0; i < ARRAY_SIZE(rings); i++)
>> +		enet_write(enet, rings[i]->cfg_block + ENET_DMA_CH_CFG, 0);
>> +	enet_maskset(enet, ENET_DMA_CONTROLLER_CFG, ENET_DMA_CTRL_CFG_MASTER_EN, 0);
> 
> Is there a need to wait for any in flight DMA transfers to complete
> before you go further? Or is that what
> bcm4908_enet_dma_rx_ring_disable() is doing?

bcm4908_enet_dma_rx_ring_disable() checks for DMA to "confirm" it got stopped.


>> +
>> +	/* Reset channels state */
>> +	for (i = 0; i < ARRAY_SIZE(rings); i++) {
>> +		struct bcm4908_enet_dma_ring *ring = rings[i];
>> +
>> +		enet_write(enet, ring->st_ram_block + ENET_DMA_CH_STATE_RAM_BASE_DESC_PTR, 0);
>> +		enet_write(enet, ring->st_ram_block + ENET_DMA_CH_STATE_RAM_STATE_DATA, 0);
>> +		enet_write(enet, ring->st_ram_block + ENET_DMA_CH_STATE_RAM_DESC_LEN_STATUS, 0);
>> +		enet_write(enet, ring->st_ram_block + ENET_DMA_CH_STATE_RAM_DESC_BASE_BUFPTR, 0);
>> +	}
>> +}
>> +
>> +static void bcm4908_enet_dma_tx_ring_ensable(struct bcm4908_enet *enet,
>> +					     struct bcm4908_enet_dma_ring *ring)
> 
> enable not ensable?

Absolutely :)


>> +static int bcm4908_enet_open(struct net_device *netdev)
>> +{
>> +	struct bcm4908_enet *enet = netdev_priv(netdev);
>> +	struct device *dev = enet->dev;
>> +	int err;
>> +
>> +	err = request_irq(netdev->irq, bcm4908_enet_irq_handler, 0, "enet", enet);
>> +	if (err) {
>> +		dev_err(dev, "Failed to request IRQ %d: %d\n", netdev->irq, err);
>> +		return err;
>> +	}
>> +
>> +	bcm4908_enet_gmac_init(enet);
>> +	bcm4908_enet_dma_reset(enet);
>> +	bcm4908_enet_dma_init(enet);
>> +
>> +	enet_umac_set(enet, UMAC_CMD, CMD_TX_EN | CMD_RX_EN);
>> +
>> +	enet_set(enet, ENET_DMA_CONTROLLER_CFG, ENET_DMA_CTRL_CFG_MASTER_EN);
>> +	enet_maskset(enet, ENET_DMA_CONTROLLER_CFG, ENET_DMA_CTRL_CFG_FLOWC_CH1_EN, 0);
>> +	bcm4908_enet_dma_rx_ring_enable(enet, &enet->rx_ring);
>> +
>> +	napi_enable(&enet->napi);
>> +	netif_carrier_on(netdev);
>> +	netif_start_queue(netdev);
>> +
>> +	bcm4908_enet_intrs_ack(enet);
>> +	bcm4908_enet_intrs_on(enet);
>> +
>> +	return 0;
>> +}
> 
> No PHY handling? It would be normal to connect the phy in open.

I believe so, this controller is integrated into SoC and is always connected
to the (internal) switch port. It uses a fixed link.