<linux kernel> RT8139c+ driver

最新推荐文章于 2025-08-18 22:01:01 发布

sunzixun

最新推荐文章于 2025-08-18 22:01:01 发布

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本文链接：https://blog.youkuaiyun.com/sunzixun/article/details/84162737

本文详细解析了8139网卡驱动的工作原理，包括DMA数据传输过程、NAPI模式下的中断处理机制及ring descriptors的管理。探讨了如何通过dma_alloc_coherent分配内存、设置中断屏蔽寄存器以及具体的DMA数据搬运流程。

摘要生成于 C知道，由 DeepSeek-R1 满血版支持，前往体验 >

NIC register

IntrStatus = 0x3E, /* Interrupt status */

int cp_init_one (struct pci_dev *pdev, const struct pci_device_id *ent)

|- dev->irq = pdev->irq;

Int Cp_open(struct net_device *dev)

|-Request_irq(dev->irq, cp_interrupt, IRQF_SHARED, dev->name , dev);

#define cpr16(reg) readw(cp->regs + (reg))

cp_norx_intr_mask = PciErr | LinkChg | TxOK | TxErr | TxEmpty,

Irqreturn_t cp_interrupt(int irq, void *dev_instance){

//...

if (status & (RxOK | RxErr | RxEmpty | RxFIFOOvr))

if (napi_schedule_prep(&cp->napi)) {

// 关闭 recv中断相关寄存器进入NAPI模式

cpw16_f(IntrMask, cp_norx_intr_mask);

__napi_schedule(&cp->napi);

|-____napi_schedule(&__get_cpu_var(softnet_data), n);

|- __raise_softirq_irqoff(NET_RX_SOFTIRQ);

}

status = cpr16(IntrStatus);

//...

}

static inline int napi_schedule_prep(struct napi_struct *n)

|-test_and_set_bit(NAPI_STATE_SCHED, &n->state);

:/proc/sys/net/core$ cat netdev_budget 300

Static void net_rx_action(struct softirq_action *h){

struct softnet_data *sd = &__get_cpu_var(softnet_data);

while (!list_empty(&sd->poll_list)) {

//...

if (test_bit(NAPI_STATE_SCHED, &n->state)) {

work = n->poll(n, weight);

trace_napi_poll(n);

}

WARN_ON_ONCE(work > weight);

budget -= work; //你懂的

//..

}

Recall to :

process_backlog()

|-struct softnet_data *sd = container_of(napi, struct softnet_data, backlog);

|-__netif_receive_skb

// ok 忘记吧!

-----------------------------------------------------------------------------------------------------

Here we back to 8139 driver :

// 开始从DMA 搬运到 cp->rx_skb

void cp_rx_poll(struct napi_struct *napi, int budget){

//...

While(1){

const unsigned buflen = cp->rx_buf_sz;

skb = cp->rx_skb[rx_tail];

len = (status & 0x1fff) - 4; //CRC

// |- cp_change_mtu(); -> cp_set_rxbufsize();

new_skb = netdev_alloc_skb_ip_align(dev, buflen);

|-__netdev_alloc_skb+GFP_ATOMIC

|-skb_reserve+NET_IP_ALIGN

/*ummpa上次的dma 地址 last transfer is done */

dma_unmap_single(&cp->pdev->dev, mapping, buflen, PCI_DMA_FROMDEVICE);

skb_put(skb, len);

/*用new_skb->data做为下一次的mapping 并保存*/

mapping = dma_map_single(&cp->pdev->dev, new_skb->data, buflen,PCI_DMA_FROMDEVICE);

/*记录在 rx_skb数组tail*/

cp->rx_skb[rx_tail] = new_skb;

cp_rx_skb(cp, skb, desc);

|-__napi_gro_receive 使用GRO开始做拆包的组装

|-dev_gro_receive

|-ptype->gro_receive(&napi->gro_list, skb); 先是inet_gro_receive 接下来如果tcp 注册的是tcp4_gro_receive skb都存到了skb_shared_info frags上

cp->rx_ring[rx_tail].opts2 = 0;

cp->rx_ring[rx_tail].addr = cpu_to_le64(mapping);

//some statistics

if (rx < budget) {// done !}

}

//...

}

The streaming DMA mapping routines can be called from interrupt context.

不需要CPU 和device 之间 in parallel access

This of "streaming" as "asynchronous" or "outside the coherency domain".

对于 ring descriptors 需要Consistent DMA

static int cp_alloc_rings (struct cp_private *cp)
{
	void *mem;

	mem = dma_alloc_coherent(&cp->pdev->dev, CP_RING_BYTES,
				 &cp->ring_dma, GFP_KERNEL);
	if (!mem)
		return -ENOMEM;
// 记住操作此mem 如果不想发生奇怪的事情一定要wmb()一下！
	cp->rx_ring = mem;
	cp->tx_ring = &cp->rx_ring[CP_RX_RING_SIZE];//64

	return cp_init_rings(cp);

这里就要说一下8139c+的 transmit receive mode了

rtl8139c+ 为收发单独提供了【64】个连续的内存描述符有3种ring 描述符，

1 高优先级传输ring

2 正常优先级传输ring

3 正常接收ring

每一个ring描述符由4个连续的双字组成 ,开始地址也需要256位对齐，这里可以看到预先用consistent DMA分配了这块

下面是区段对这个的定义，很简单？ NO

struct cp_desc {
	__le32		opts1;
	__le32		opts2;
	__le64		addr;
};

事实上应该如此：

分配ring 数组

int cp_alloc_rings(struct cp_private *cp)

|- dma_alloc_coherent + GFP_KERNEL

|- __get_free_pages /

-----------------------------------------------------------

E2prom :

cp_get_eeprom(struct net_device *dev,

struct ethtool_eeprom *eeprom, u8 *data)

addr_len = read_eeprom(cp->regs, 0, 8) == 0x8129 ? 8 : 6;