PCI设备的扫描是基于深度优先搜索算法(DFS:Depth First Search),也就是说,下级分支最多的PCI桥将最先完成其子设备的扫描。下面我们以图片来具体说明,BIOS是如何一步步完成PCI 设备扫描的。
第一步:
PCI Host 主桥扫描Bus 0上的设备(在一个处理器系统中,一般将与HOST主桥直接相连的PCI总线被命名为PCI Bus 0),系统首先会忽略Bus 0上的D1,D2等不会挂接PCI桥的设备,主桥发现Bridge 1后,将Bridge1 下面的PCI Bus定为 Bus 1,系统将初始化Bridge 1的配置空间,并将该桥的Primary Bus Number 和 Secondary Bus Number寄存器分别设置成0和1,以表明Bridge1 的上游总线是0,下游总线是1,由于还无法确定Bridge1下挂载设备的具体情况,系统先暂时将Subordinate Bus Number设为0xFF。如下图所示:
第二步:
系统开始扫描Bus 1,将会发现Bridge 2。系统将Bridge 2下面的PCI Bus定为Bus 2,并将该桥的Primary Bus Number 和 Secondary Bus Number寄存器分别设置成1和2,和上一步一样暂时把Bridge 2 的Subordinate Bus Number设为0xFF。如下图所示:
第三步:
系统继续扫描Bus 2,将会发现Bridge 4。系统将Bridge 4下面的PCI Bus定为Bus 3,并将该桥的Primary Bus Number 和 Secondary Bus Number寄存器分别设置成2和3,此后
系统继续扫描后发现Bus 3 下面已经没有任何Bridge了,意味着该PCI总线下已经没有任何挂载下游总线了,因此Bridge 4的Subordinate Bus Number的值已经可以确定为3了。
如下图所示:
第四步:
完成Bus 3的扫描后,系统返回到Bus 2继续扫描,发现Bus 2下面已经没有其他Bridge了。此时Bridge 2的Subordinate Bus Number的值也已经可以确定为3了。如下图所示:
第五步:
完成Bus 2的扫描后,系统返回到Bus1继续扫描,会发现Bridge 3,系统将Bridge 3下面的PCI Bus定为Bus 4。并将Bridge 4的Primary Bus Number 和 Secondary Bus Number寄存器分别设置成1和4,此后系统继续扫描后发现Bus 4 下面已经没有任何Bridge了,意味着该PCI总线下已经没有挂载任何下游总线了,因此Bridge 3 的Subordinate Bus Number的值已经可以确定为4了。如下图所示:
第六步:
完成Bus 4的扫描后,系统返回到Bus 1继续扫描, 发现Bus 1下面已经没有其他Bridge了。此时Bridge 1的Subordinate Bus Number的值已经可以确定为4,系统返回Bus 0继续扫描(Bus 0下如果有其他它Bridge,将重复上述的步骤进行扫描)。至此,本例中的整个PCI的设备扫描已经完成了。最终的设备和总线的扫描结果如下图所示。
了解了上面PCI设备扫描的大概流程,我们接下来看看Bios代码中具体是如何实现这些扫描的。
一般来说,我们可以通过两个寄存器来访问PCI的配置空间(寄存器CONFIG_ADDRESS与CONFIG_DATA),在x86体系下,这两个寄存器分别对应0xCF8和0xCFC端口,对配置空间的访问都是通过对这两个寄存器的读写来实现先。CONFIG_ADDRESS寄存器的具体位组成如下图所示:
Bus Number : 总线号(8 bit),范围0--255。
Device Number: 设备号(5 bit),范围0--31。
Function Number: 功能号(3 bit),范围0--7。
Register Number: 寄存器号(6 bit),范围0--63 (配置空间一共256个字节,分割成64个4字节的寄存器,从0--63编号)。
每个PCI设备可根据上图所示的四个信息:Bus Number, Device Number, Function Number,Register Number 来进行具体设备的定位并对其配置空间访问。当我们要访问PCI设备的配置空间时,先根据以上格式设置CONFIG_ADDRESS寄存器,然后再读取CONFIG_DATA寄存器即可得到相应的配置空间寄存器的值。
因此,BIOS中PCI配置空间的读写可以封装成下面的函数:
[cpp]
1. static inline
2. {
3. outl(dev | reg, 0xcf8);
4. return
5. }
6.
7. static inline void
8. {
9. outl(dev | reg, 0xcf8);
10. outl(val, 0xcfc);
11. }
static inline uint32_t pci_config_read32(pci_addr dev, uint8_t reg)
{
outl(dev | reg, 0xcf8);
return inl(0xcfc | reg);
}
static inline void pci_config_write32(pci_addr dev, uint8_t reg, uint32_t val)
{
outl(dev | reg, 0xcf8);
outl(val, 0xcfc);
}
总体来说。该BIOS扫描过程中调用如下几个主要的函数:
ob_pci_init ----> ob_scan_pci_bus ----> pci_find_device ----> ob_pci_configure
下面我们来具体看看代码,首先BIOS执行ob_pci_init(void)函数
[cpp]
1. int ob_pci_init(void)
2. {
3. int
4. long
5. char
6.
7. #ifdef CONFIG_DEBUG_PCI
8. "Initializing PCI devices...\n");
9. #endif
10.
11. /* brute force bus scan */
12.
13. /* Find all PCI bridges */
14.
15. //获取系统指定的memeory与I/O空间的范围,分配给PCIe设备。
16. mem_base = arch->mem_base;
17. /* I/O ports under 0x400 are used by devices mapped at fixed
18. location. */
19. io_base = arch->io_base + 0x400;
20. "");
21.
22. /*遍历256条总线*/
23. for
24. ob_scan_pci_bus(bus, &mem_base, &io_base, &path);
25. }
26. free(path);
27. return
28. }
int ob_pci_init(void)
{
int bus;
unsigned long mem_base, io_base;
char *path;
#ifdef CONFIG_DEBUG_PCI
printk("Initializing PCI devices...\n");
#endif
/* brute force bus scan */
/* Find all PCI bridges */
//获取系统指定的memeory与I/O空间的范围,分配给PCIe设备。
mem_base = arch->mem_base;
/* I/O ports under 0x400 are used by devices mapped at fixed
location. */
io_base = arch->io_base + 0x400;
path = strdup("");
/*遍历256条总线*/
for (bus = 0; bus<0x100; bus++) {
ob_scan_pci_bus(bus, &mem_base, &io_base, &path);
}
free(path);
return 0;
}
总线扫描具体实现:
[cpp]
1. static void ob_scan_pci_bus(int bus, unsigned long
2. long *io_base, char
3. {
4. int
5. int
6. pci_addr addr;
7. pci_config_t config;
8. const
9. uint32_t ccode;
10. class, subclass, iface, rev;
11.
12. "/");
13. for
14. is_multi = 0;
15. for
16. #ifdef CONFIG_XBOX
17. if
18. continue;
19. #endif
20. /*获取设备配置空间地址*/
21. /*获取Vendor ID*/
22. /*获取Device ID*/
23.
24. if
25. continue;
26.
27. ccode = pci_config_read16(addr, PCI_CLASS_DEVICE);
28. class
29. subclass = ccode;
30. iface = pci_config_read8(addr, PCI_CLASS_PROG);
31. rev = pci_config_read8(addr, PCI_REVISION_ID);
32.
33. class, subclass, iface,/*具体设备查找以及初始化*/
34. vid, did);
35.
36. #ifdef CONFIG_DEBUG_PCI
37. "%x:%x.%x - %x:%x - ", bus, devnum, fn,
38. vid, did);
39. #endif
40. htype = pci_config_read8(addr, PCI_HEADER_TYPE);
41. if
42. is_multi = htype & 0x80;
43.
44. if
45. sizeof(config.path),
46. "%s/pci%x,%x", *path, vid, did);
47. else
48. sizeof(config.path),
49. "%s/%s", *path, pci_dev->name);
50. #ifdef CONFIG_DEBUG_PCI
51. "%s - ", config.path);
52. #endif
53. config.dev = addr & 0x00FFFFFF;
54.
55. REGISTER_NAMED_NODE(ob_pci_node, config.path);
56.
57. activate_device(config.path);
58.
59. /*配置设备的配置空间*/
60. ob_pci_add_properties(addr, pci_dev, &config);
61.
62. if (class
63. (subclass == PCI_SUBCLASS_BRIDGE_HOST ||
64. subclass == PCI_SUBCLASS_BRIDGE_PCI)) {
65. /* host or bridge */
66. free(*path);
67. *path = strdup(config.path);
68. }
69.
70. }
71. }
72. device_end();
73. }
static void ob_scan_pci_bus(int bus, unsigned long *mem_base,
unsigned long *io_base, char **path)
{
int devnum, fn, is_multi, vid, did;
unsigned int htype;
pci_addr addr;
pci_config_t config;
const pci_dev_t *pci_dev;
uint32_t ccode;
uint8_t class, subclass, iface, rev;
activate_device("/");
for (devnum = 0; devnum < 32; devnum++) {
is_multi = 0;
for (fn = 0; fn==0 || (is_multi && fn<8); fn++) {
#ifdef CONFIG_XBOX
if (pci_xbox_blacklisted (bus, devnum, fn))
continue;
#endif
addr = PCI_ADDR(bus, devnum, fn); /*获取设备配置空间地址*/
vid = pci_config_read16(addr, PCI_VENDOR_ID); /*获取Vendor ID*/
did = pci_config_read16(addr, PCI_DEVICE_ID); /*获取Device ID*/
if (vid==0xffff || vid==0)
continue;
ccode = pci_config_read16(addr, PCI_CLASS_DEVICE);
class = ccode >> 8;
subclass = ccode;
iface = pci_config_read8(addr, PCI_CLASS_PROG);
rev = pci_config_read8(addr, PCI_REVISION_ID);
pci_dev = pci_find_device(class, subclass, iface,/*具体设备查找以及初始化*/
vid, did);
#ifdef CONFIG_DEBUG_PCI
printk("%x:%x.%x - %x:%x - ", bus, devnum, fn,
vid, did);
#endif
htype = pci_config_read8(addr, PCI_HEADER_TYPE);
if (fn == 0)
is_multi = htype & 0x80;
if (pci_dev == NULL || pci_dev->name == NULL)
snprintf(config.path, sizeof(config.path),
"%s/pci%x,%x", *path, vid, did);
else
snprintf(config.path, sizeof(config.path),
"%s/%s", *path, pci_dev->name);
#ifdef CONFIG_DEBUG_PCI
printk("%s - ", config.path);
#endif
config.dev = addr & 0x00FFFFFF;
REGISTER_NAMED_NODE(ob_pci_node, config.path);
activate_device(config.path);
ob_pci_configure(addr, &config, mem_base, io_base); /*配置设备的配置空间*/
ob_pci_add_properties(addr, pci_dev, &config);
if (class == PCI_BASE_CLASS_BRIDGE &&
(subclass == PCI_SUBCLASS_BRIDGE_HOST ||
subclass == PCI_SUBCLASS_BRIDGE_PCI)) {
/* host or bridge */
free(*path);
*path = strdup(config.path);
}
}
}
device_end();
}
具体某条总线上的设备扫描由以下函数实现:
[cpp]
1. <PRE class=cpp name="code">const pci_dev_t *pci_find_device (uint8_t class, uint8_t subclass,
2. uint8_t iface, uint16_t vendor,
3. uint16_t product)
4. {
5. int (*config_cb)(const
6. const
7. const
8. const
9. const
10. const void *private;
11. new;
12. const char
13.
14. "unknown";
15. "unknown";
16. config_cb = NULL;
17. private
18.
19. if (class
20. /* Special hack for old style VGA devices */
21. class
22. subclass = 0x00;
23. else if (class
24. /* Special case for misc devices */
25. dev = misc_pci;
26. goto
27. }
28. if (class > (sizeof(pci_classes) / sizeof(pci_class_t))) {
29. "invalid PCI device";
30. "invalid";
31. goto
32. }
33. class];
34. name = pclass->name;
35. type = pclass->type;
36. for
37. if
38. goto
39. if
40. if
41. name = psubclass->name;
42. if
43. type = psubclass->type;
44. if
45. config_cb = psubclass->config_cb;
46. }
47. if (psubclass->private
48. private = psubclass->private;
49. if
50. break;
51. dev = psubclass->devices;
52. goto
53. }
54. }
55. for
56. if
57. dev = psubclass->devices;
58. break;
59. }
60. if
61. if
62. name = piface->name;
63. if
64. type = piface->type;
65. if
66. config_cb = piface->config_cb;
67. }
68. if (piface->private
69. private = piface->private;
70. dev = piface->devices;
71. break;
72. }
73. }
74. find_device:
75. if
76. goto
77. for
78. if
79. goto
80. }
81. if
82. if
83. name = dev->name;
84. if
85. type = dev->type;
86. if
87. config_cb = dev->config_cb;
88. }
89. if (dev->private
90. private = dev->private;
91. new = malloc(sizeof(pci_dev_t));
92. if (new
93. return
94. new->vendor = vendor;
95. new->product = product;
96. new->type = type;
97. new->name = name;
98. new->model = dev->model;
99. new->compat = dev->compat;
100. new->acells = dev->acells;
101. new->scells = dev->scells;
102. new->icells = dev->icells;
103. new->config_cb = config_cb;
104. new->private = private;
105.
106. return new;
107. }
108. }
109. bad_device:
110. "Cannot manage '%s' PCI device type '%s':\n %x %x (%x %x %x)\n",
111. class, subclass, iface);
112.
113. return
114. }
115.
116.
117.
118. 配置具体设备的配置空间
119.
120. static void ob_pci_configure(pci_addr addr, pci_config_t *config, unsigned long
121. long
122.
123. {
124. uint32_t smask, omask, amask, size, reloc, min_align;
125. long
126. pci_addr config_addr;
127. int
128. uint8_t irq_pin, irq_line;
129.
130. /*配置中断引脚与中断编号*/
131. irq_pin = pci_config_read8(addr, PCI_INTERRUPT_PIN);
132. if
133. config->irq_pin = irq_pin;
134. irq_pin = (((config->dev >> 11) & 0x1F) + irq_pin - 1) & 3;
135. irq_line = arch->irqs[irq_pin];
136. pci_config_write8(addr, PCI_INTERRUPT_LINE, irq_line);
137. config->irq_line = irq_line;
138. else
139. config->irq_line = -1;
140.
141. /*配置memory空间和I/O空间*/
142. omask = 0x00000000;
143. for
144.
145. config->assigned[reg] = 0x00000000;
146. config->sizes[reg] = 0x00000000;
147.
148. if
149. /* 64 bits memory mapping */
150. continue;
151. }
152.
153. if
154. config_addr = PCI_ROM_ADDRESS;
155. else
156. config_addr = PCI_BASE_ADDR_0 + reg * 4;
157.
158. config->regions[reg] = pci_config_read32(addr, config_addr);
159.
160. /* get region size */
161.
162. pci_config_write32(addr, config_addr, 0xffffffff);
163. smask = pci_config_read32(addr, config_addr);
164. if
165. continue;
166.
167. if
168. /* I/O space */
169. base = *io_base;
170. min_align = 1 << 7;
171. amask = 0x00000001;
172. pci_config_write16(addr, PCI_COMMAND,
173. pci_config_read16(addr,
174. PCI_COMMAND) |
175. PCI_COMMAND_IO);
176. else
177. /* Memory Space */
178. base = *mem_base;
179. min_align = 1 << 16;
180. amask = 0x0000000F;
181. if
182. /* ROM */
183. }
184. pci_config_write16(addr, PCI_COMMAND,
185. pci_config_read16(addr,
186. PCI_COMMAND) |
187. PCI_COMMAND_MEMORY);
188. }
189. omask = smask & amask;
190. smask &= ~amask;
191. size = (~smask) + 1;
192. config->sizes[reg] = size;
193. reloc = base;
194. if
195. size = min_align;
196. reloc = (reloc + size -1) & ~(size - 1);
197. if
198. *io_base = reloc + size;
199. reloc -= arch->io_base;
200. else
201. *mem_base = reloc + size;
202. }
203. pci_config_write32(addr, config_addr, reloc | omask);
204. config->assigned[reg] = reloc | omask;
205. }
206. }
207.
208. 通过以上这些步骤,Bios就完成了所有PCI设备的扫描,并且为每个设备分配好了系统资源。<BR>
209. </PRE>
210. <PRE></PRE>