xref: /openbmc/linux/arch/x86/kernel/amd_nb.c (revision 2fa5ebe3)
1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3  * Shared support code for AMD K8 northbridges and derivatives.
4  * Copyright 2006 Andi Kleen, SUSE Labs.
5  */
6 
7 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
8 
9 #include <linux/types.h>
10 #include <linux/slab.h>
11 #include <linux/init.h>
12 #include <linux/errno.h>
13 #include <linux/export.h>
14 #include <linux/spinlock.h>
15 #include <linux/pci_ids.h>
16 #include <asm/amd_nb.h>
17 
18 #define PCI_DEVICE_ID_AMD_17H_ROOT	0x1450
19 #define PCI_DEVICE_ID_AMD_17H_M10H_ROOT	0x15d0
20 #define PCI_DEVICE_ID_AMD_17H_M30H_ROOT	0x1480
21 #define PCI_DEVICE_ID_AMD_17H_M60H_ROOT	0x1630
22 #define PCI_DEVICE_ID_AMD_17H_MA0H_ROOT	0x14b5
23 #define PCI_DEVICE_ID_AMD_19H_M10H_ROOT	0x14a4
24 #define PCI_DEVICE_ID_AMD_19H_M60H_ROOT	0x14d8
25 #define PCI_DEVICE_ID_AMD_19H_M70H_ROOT	0x14e8
26 #define PCI_DEVICE_ID_AMD_17H_DF_F4	0x1464
27 #define PCI_DEVICE_ID_AMD_17H_M10H_DF_F4 0x15ec
28 #define PCI_DEVICE_ID_AMD_17H_M30H_DF_F4 0x1494
29 #define PCI_DEVICE_ID_AMD_17H_M60H_DF_F4 0x144c
30 #define PCI_DEVICE_ID_AMD_17H_M70H_DF_F4 0x1444
31 #define PCI_DEVICE_ID_AMD_17H_MA0H_DF_F4 0x1728
32 #define PCI_DEVICE_ID_AMD_19H_DF_F4	0x1654
33 #define PCI_DEVICE_ID_AMD_19H_M10H_DF_F4 0x14b1
34 #define PCI_DEVICE_ID_AMD_19H_M40H_ROOT	0x14b5
35 #define PCI_DEVICE_ID_AMD_19H_M40H_DF_F4 0x167d
36 #define PCI_DEVICE_ID_AMD_19H_M50H_DF_F4 0x166e
37 #define PCI_DEVICE_ID_AMD_19H_M60H_DF_F4 0x14e4
38 #define PCI_DEVICE_ID_AMD_19H_M70H_DF_F4 0x14f4
39 
40 /* Protect the PCI config register pairs used for SMN. */
41 static DEFINE_MUTEX(smn_mutex);
42 
43 static u32 *flush_words;
44 
45 static const struct pci_device_id amd_root_ids[] = {
46 	{ PCI_DEVICE(PCI_VENDOR_ID_AMD, PCI_DEVICE_ID_AMD_17H_ROOT) },
47 	{ PCI_DEVICE(PCI_VENDOR_ID_AMD, PCI_DEVICE_ID_AMD_17H_M10H_ROOT) },
48 	{ PCI_DEVICE(PCI_VENDOR_ID_AMD, PCI_DEVICE_ID_AMD_17H_M30H_ROOT) },
49 	{ PCI_DEVICE(PCI_VENDOR_ID_AMD, PCI_DEVICE_ID_AMD_17H_M60H_ROOT) },
50 	{ PCI_DEVICE(PCI_VENDOR_ID_AMD, PCI_DEVICE_ID_AMD_17H_MA0H_ROOT) },
51 	{ PCI_DEVICE(PCI_VENDOR_ID_AMD, PCI_DEVICE_ID_AMD_19H_M10H_ROOT) },
52 	{ PCI_DEVICE(PCI_VENDOR_ID_AMD, PCI_DEVICE_ID_AMD_19H_M40H_ROOT) },
53 	{ PCI_DEVICE(PCI_VENDOR_ID_AMD, PCI_DEVICE_ID_AMD_19H_M60H_ROOT) },
54 	{ PCI_DEVICE(PCI_VENDOR_ID_AMD, PCI_DEVICE_ID_AMD_19H_M70H_ROOT) },
55 	{}
56 };
57 
58 #define PCI_DEVICE_ID_AMD_CNB17H_F4     0x1704
59 
60 static const struct pci_device_id amd_nb_misc_ids[] = {
61 	{ PCI_DEVICE(PCI_VENDOR_ID_AMD, PCI_DEVICE_ID_AMD_K8_NB_MISC) },
62 	{ PCI_DEVICE(PCI_VENDOR_ID_AMD, PCI_DEVICE_ID_AMD_10H_NB_MISC) },
63 	{ PCI_DEVICE(PCI_VENDOR_ID_AMD, PCI_DEVICE_ID_AMD_15H_NB_F3) },
64 	{ PCI_DEVICE(PCI_VENDOR_ID_AMD, PCI_DEVICE_ID_AMD_15H_M10H_F3) },
65 	{ PCI_DEVICE(PCI_VENDOR_ID_AMD, PCI_DEVICE_ID_AMD_15H_M30H_NB_F3) },
66 	{ PCI_DEVICE(PCI_VENDOR_ID_AMD, PCI_DEVICE_ID_AMD_15H_M60H_NB_F3) },
67 	{ PCI_DEVICE(PCI_VENDOR_ID_AMD, PCI_DEVICE_ID_AMD_16H_NB_F3) },
68 	{ PCI_DEVICE(PCI_VENDOR_ID_AMD, PCI_DEVICE_ID_AMD_16H_M30H_NB_F3) },
69 	{ PCI_DEVICE(PCI_VENDOR_ID_AMD, PCI_DEVICE_ID_AMD_17H_DF_F3) },
70 	{ PCI_DEVICE(PCI_VENDOR_ID_AMD, PCI_DEVICE_ID_AMD_17H_M10H_DF_F3) },
71 	{ PCI_DEVICE(PCI_VENDOR_ID_AMD, PCI_DEVICE_ID_AMD_17H_M30H_DF_F3) },
72 	{ PCI_DEVICE(PCI_VENDOR_ID_AMD, PCI_DEVICE_ID_AMD_17H_M60H_DF_F3) },
73 	{ PCI_DEVICE(PCI_VENDOR_ID_AMD, PCI_DEVICE_ID_AMD_17H_MA0H_DF_F3) },
74 	{ PCI_DEVICE(PCI_VENDOR_ID_AMD, PCI_DEVICE_ID_AMD_CNB17H_F3) },
75 	{ PCI_DEVICE(PCI_VENDOR_ID_AMD, PCI_DEVICE_ID_AMD_17H_M70H_DF_F3) },
76 	{ PCI_DEVICE(PCI_VENDOR_ID_AMD, PCI_DEVICE_ID_AMD_19H_DF_F3) },
77 	{ PCI_DEVICE(PCI_VENDOR_ID_AMD, PCI_DEVICE_ID_AMD_19H_M10H_DF_F3) },
78 	{ PCI_DEVICE(PCI_VENDOR_ID_AMD, PCI_DEVICE_ID_AMD_19H_M40H_DF_F3) },
79 	{ PCI_DEVICE(PCI_VENDOR_ID_AMD, PCI_DEVICE_ID_AMD_19H_M50H_DF_F3) },
80 	{ PCI_DEVICE(PCI_VENDOR_ID_AMD, PCI_DEVICE_ID_AMD_19H_M60H_DF_F3) },
81 	{ PCI_DEVICE(PCI_VENDOR_ID_AMD, PCI_DEVICE_ID_AMD_19H_M70H_DF_F3) },
82 	{}
83 };
84 
85 static const struct pci_device_id amd_nb_link_ids[] = {
86 	{ PCI_DEVICE(PCI_VENDOR_ID_AMD, PCI_DEVICE_ID_AMD_15H_NB_F4) },
87 	{ PCI_DEVICE(PCI_VENDOR_ID_AMD, PCI_DEVICE_ID_AMD_15H_M30H_NB_F4) },
88 	{ PCI_DEVICE(PCI_VENDOR_ID_AMD, PCI_DEVICE_ID_AMD_15H_M60H_NB_F4) },
89 	{ PCI_DEVICE(PCI_VENDOR_ID_AMD, PCI_DEVICE_ID_AMD_16H_NB_F4) },
90 	{ PCI_DEVICE(PCI_VENDOR_ID_AMD, PCI_DEVICE_ID_AMD_16H_M30H_NB_F4) },
91 	{ PCI_DEVICE(PCI_VENDOR_ID_AMD, PCI_DEVICE_ID_AMD_17H_DF_F4) },
92 	{ PCI_DEVICE(PCI_VENDOR_ID_AMD, PCI_DEVICE_ID_AMD_17H_M10H_DF_F4) },
93 	{ PCI_DEVICE(PCI_VENDOR_ID_AMD, PCI_DEVICE_ID_AMD_17H_M30H_DF_F4) },
94 	{ PCI_DEVICE(PCI_VENDOR_ID_AMD, PCI_DEVICE_ID_AMD_17H_M60H_DF_F4) },
95 	{ PCI_DEVICE(PCI_VENDOR_ID_AMD, PCI_DEVICE_ID_AMD_17H_M70H_DF_F4) },
96 	{ PCI_DEVICE(PCI_VENDOR_ID_AMD, PCI_DEVICE_ID_AMD_17H_MA0H_DF_F4) },
97 	{ PCI_DEVICE(PCI_VENDOR_ID_AMD, PCI_DEVICE_ID_AMD_19H_DF_F4) },
98 	{ PCI_DEVICE(PCI_VENDOR_ID_AMD, PCI_DEVICE_ID_AMD_19H_M10H_DF_F4) },
99 	{ PCI_DEVICE(PCI_VENDOR_ID_AMD, PCI_DEVICE_ID_AMD_19H_M40H_DF_F4) },
100 	{ PCI_DEVICE(PCI_VENDOR_ID_AMD, PCI_DEVICE_ID_AMD_19H_M50H_DF_F4) },
101 	{ PCI_DEVICE(PCI_VENDOR_ID_AMD, PCI_DEVICE_ID_AMD_CNB17H_F4) },
102 	{}
103 };
104 
105 static const struct pci_device_id hygon_root_ids[] = {
106 	{ PCI_DEVICE(PCI_VENDOR_ID_HYGON, PCI_DEVICE_ID_AMD_17H_ROOT) },
107 	{}
108 };
109 
110 static const struct pci_device_id hygon_nb_misc_ids[] = {
111 	{ PCI_DEVICE(PCI_VENDOR_ID_HYGON, PCI_DEVICE_ID_AMD_17H_DF_F3) },
112 	{}
113 };
114 
115 static const struct pci_device_id hygon_nb_link_ids[] = {
116 	{ PCI_DEVICE(PCI_VENDOR_ID_HYGON, PCI_DEVICE_ID_AMD_17H_DF_F4) },
117 	{}
118 };
119 
120 const struct amd_nb_bus_dev_range amd_nb_bus_dev_ranges[] __initconst = {
121 	{ 0x00, 0x18, 0x20 },
122 	{ 0xff, 0x00, 0x20 },
123 	{ 0xfe, 0x00, 0x20 },
124 	{ }
125 };
126 
127 static struct amd_northbridge_info amd_northbridges;
128 
129 u16 amd_nb_num(void)
130 {
131 	return amd_northbridges.num;
132 }
133 EXPORT_SYMBOL_GPL(amd_nb_num);
134 
135 bool amd_nb_has_feature(unsigned int feature)
136 {
137 	return ((amd_northbridges.flags & feature) == feature);
138 }
139 EXPORT_SYMBOL_GPL(amd_nb_has_feature);
140 
141 struct amd_northbridge *node_to_amd_nb(int node)
142 {
143 	return (node < amd_northbridges.num) ? &amd_northbridges.nb[node] : NULL;
144 }
145 EXPORT_SYMBOL_GPL(node_to_amd_nb);
146 
147 static struct pci_dev *next_northbridge(struct pci_dev *dev,
148 					const struct pci_device_id *ids)
149 {
150 	do {
151 		dev = pci_get_device(PCI_ANY_ID, PCI_ANY_ID, dev);
152 		if (!dev)
153 			break;
154 	} while (!pci_match_id(ids, dev));
155 	return dev;
156 }
157 
158 static int __amd_smn_rw(u16 node, u32 address, u32 *value, bool write)
159 {
160 	struct pci_dev *root;
161 	int err = -ENODEV;
162 
163 	if (node >= amd_northbridges.num)
164 		goto out;
165 
166 	root = node_to_amd_nb(node)->root;
167 	if (!root)
168 		goto out;
169 
170 	mutex_lock(&smn_mutex);
171 
172 	err = pci_write_config_dword(root, 0x60, address);
173 	if (err) {
174 		pr_warn("Error programming SMN address 0x%x.\n", address);
175 		goto out_unlock;
176 	}
177 
178 	err = (write ? pci_write_config_dword(root, 0x64, *value)
179 		     : pci_read_config_dword(root, 0x64, value));
180 	if (err)
181 		pr_warn("Error %s SMN address 0x%x.\n",
182 			(write ? "writing to" : "reading from"), address);
183 
184 out_unlock:
185 	mutex_unlock(&smn_mutex);
186 
187 out:
188 	return err;
189 }
190 
191 int amd_smn_read(u16 node, u32 address, u32 *value)
192 {
193 	return __amd_smn_rw(node, address, value, false);
194 }
195 EXPORT_SYMBOL_GPL(amd_smn_read);
196 
197 int amd_smn_write(u16 node, u32 address, u32 value)
198 {
199 	return __amd_smn_rw(node, address, &value, true);
200 }
201 EXPORT_SYMBOL_GPL(amd_smn_write);
202 
203 
204 static int amd_cache_northbridges(void)
205 {
206 	const struct pci_device_id *misc_ids = amd_nb_misc_ids;
207 	const struct pci_device_id *link_ids = amd_nb_link_ids;
208 	const struct pci_device_id *root_ids = amd_root_ids;
209 	struct pci_dev *root, *misc, *link;
210 	struct amd_northbridge *nb;
211 	u16 roots_per_misc = 0;
212 	u16 misc_count = 0;
213 	u16 root_count = 0;
214 	u16 i, j;
215 
216 	if (amd_northbridges.num)
217 		return 0;
218 
219 	if (boot_cpu_data.x86_vendor == X86_VENDOR_HYGON) {
220 		root_ids = hygon_root_ids;
221 		misc_ids = hygon_nb_misc_ids;
222 		link_ids = hygon_nb_link_ids;
223 	}
224 
225 	misc = NULL;
226 	while ((misc = next_northbridge(misc, misc_ids)))
227 		misc_count++;
228 
229 	if (!misc_count)
230 		return -ENODEV;
231 
232 	root = NULL;
233 	while ((root = next_northbridge(root, root_ids)))
234 		root_count++;
235 
236 	if (root_count) {
237 		roots_per_misc = root_count / misc_count;
238 
239 		/*
240 		 * There should be _exactly_ N roots for each DF/SMN
241 		 * interface.
242 		 */
243 		if (!roots_per_misc || (root_count % roots_per_misc)) {
244 			pr_info("Unsupported AMD DF/PCI configuration found\n");
245 			return -ENODEV;
246 		}
247 	}
248 
249 	nb = kcalloc(misc_count, sizeof(struct amd_northbridge), GFP_KERNEL);
250 	if (!nb)
251 		return -ENOMEM;
252 
253 	amd_northbridges.nb = nb;
254 	amd_northbridges.num = misc_count;
255 
256 	link = misc = root = NULL;
257 	for (i = 0; i < amd_northbridges.num; i++) {
258 		node_to_amd_nb(i)->root = root =
259 			next_northbridge(root, root_ids);
260 		node_to_amd_nb(i)->misc = misc =
261 			next_northbridge(misc, misc_ids);
262 		node_to_amd_nb(i)->link = link =
263 			next_northbridge(link, link_ids);
264 
265 		/*
266 		 * If there are more PCI root devices than data fabric/
267 		 * system management network interfaces, then the (N)
268 		 * PCI roots per DF/SMN interface are functionally the
269 		 * same (for DF/SMN access) and N-1 are redundant.  N-1
270 		 * PCI roots should be skipped per DF/SMN interface so
271 		 * the following DF/SMN interfaces get mapped to
272 		 * correct PCI roots.
273 		 */
274 		for (j = 1; j < roots_per_misc; j++)
275 			root = next_northbridge(root, root_ids);
276 	}
277 
278 	if (amd_gart_present())
279 		amd_northbridges.flags |= AMD_NB_GART;
280 
281 	/*
282 	 * Check for L3 cache presence.
283 	 */
284 	if (!cpuid_edx(0x80000006))
285 		return 0;
286 
287 	/*
288 	 * Some CPU families support L3 Cache Index Disable. There are some
289 	 * limitations because of E382 and E388 on family 0x10.
290 	 */
291 	if (boot_cpu_data.x86 == 0x10 &&
292 	    boot_cpu_data.x86_model >= 0x8 &&
293 	    (boot_cpu_data.x86_model > 0x9 ||
294 	     boot_cpu_data.x86_stepping >= 0x1))
295 		amd_northbridges.flags |= AMD_NB_L3_INDEX_DISABLE;
296 
297 	if (boot_cpu_data.x86 == 0x15)
298 		amd_northbridges.flags |= AMD_NB_L3_INDEX_DISABLE;
299 
300 	/* L3 cache partitioning is supported on family 0x15 */
301 	if (boot_cpu_data.x86 == 0x15)
302 		amd_northbridges.flags |= AMD_NB_L3_PARTITIONING;
303 
304 	return 0;
305 }
306 
307 /*
308  * Ignores subdevice/subvendor but as far as I can figure out
309  * they're useless anyways
310  */
311 bool __init early_is_amd_nb(u32 device)
312 {
313 	const struct pci_device_id *misc_ids = amd_nb_misc_ids;
314 	const struct pci_device_id *id;
315 	u32 vendor = device & 0xffff;
316 
317 	if (boot_cpu_data.x86_vendor != X86_VENDOR_AMD &&
318 	    boot_cpu_data.x86_vendor != X86_VENDOR_HYGON)
319 		return false;
320 
321 	if (boot_cpu_data.x86_vendor == X86_VENDOR_HYGON)
322 		misc_ids = hygon_nb_misc_ids;
323 
324 	device >>= 16;
325 	for (id = misc_ids; id->vendor; id++)
326 		if (vendor == id->vendor && device == id->device)
327 			return true;
328 	return false;
329 }
330 
331 struct resource *amd_get_mmconfig_range(struct resource *res)
332 {
333 	u32 address;
334 	u64 base, msr;
335 	unsigned int segn_busn_bits;
336 
337 	if (boot_cpu_data.x86_vendor != X86_VENDOR_AMD &&
338 	    boot_cpu_data.x86_vendor != X86_VENDOR_HYGON)
339 		return NULL;
340 
341 	/* assume all cpus from fam10h have mmconfig */
342 	if (boot_cpu_data.x86 < 0x10)
343 		return NULL;
344 
345 	address = MSR_FAM10H_MMIO_CONF_BASE;
346 	rdmsrl(address, msr);
347 
348 	/* mmconfig is not enabled */
349 	if (!(msr & FAM10H_MMIO_CONF_ENABLE))
350 		return NULL;
351 
352 	base = msr & (FAM10H_MMIO_CONF_BASE_MASK<<FAM10H_MMIO_CONF_BASE_SHIFT);
353 
354 	segn_busn_bits = (msr >> FAM10H_MMIO_CONF_BUSRANGE_SHIFT) &
355 			 FAM10H_MMIO_CONF_BUSRANGE_MASK;
356 
357 	res->flags = IORESOURCE_MEM;
358 	res->start = base;
359 	res->end = base + (1ULL<<(segn_busn_bits + 20)) - 1;
360 	return res;
361 }
362 
363 int amd_get_subcaches(int cpu)
364 {
365 	struct pci_dev *link = node_to_amd_nb(topology_die_id(cpu))->link;
366 	unsigned int mask;
367 
368 	if (!amd_nb_has_feature(AMD_NB_L3_PARTITIONING))
369 		return 0;
370 
371 	pci_read_config_dword(link, 0x1d4, &mask);
372 
373 	return (mask >> (4 * cpu_data(cpu).cpu_core_id)) & 0xf;
374 }
375 
376 int amd_set_subcaches(int cpu, unsigned long mask)
377 {
378 	static unsigned int reset, ban;
379 	struct amd_northbridge *nb = node_to_amd_nb(topology_die_id(cpu));
380 	unsigned int reg;
381 	int cuid;
382 
383 	if (!amd_nb_has_feature(AMD_NB_L3_PARTITIONING) || mask > 0xf)
384 		return -EINVAL;
385 
386 	/* if necessary, collect reset state of L3 partitioning and BAN mode */
387 	if (reset == 0) {
388 		pci_read_config_dword(nb->link, 0x1d4, &reset);
389 		pci_read_config_dword(nb->misc, 0x1b8, &ban);
390 		ban &= 0x180000;
391 	}
392 
393 	/* deactivate BAN mode if any subcaches are to be disabled */
394 	if (mask != 0xf) {
395 		pci_read_config_dword(nb->misc, 0x1b8, &reg);
396 		pci_write_config_dword(nb->misc, 0x1b8, reg & ~0x180000);
397 	}
398 
399 	cuid = cpu_data(cpu).cpu_core_id;
400 	mask <<= 4 * cuid;
401 	mask |= (0xf ^ (1 << cuid)) << 26;
402 
403 	pci_write_config_dword(nb->link, 0x1d4, mask);
404 
405 	/* reset BAN mode if L3 partitioning returned to reset state */
406 	pci_read_config_dword(nb->link, 0x1d4, &reg);
407 	if (reg == reset) {
408 		pci_read_config_dword(nb->misc, 0x1b8, &reg);
409 		reg &= ~0x180000;
410 		pci_write_config_dword(nb->misc, 0x1b8, reg | ban);
411 	}
412 
413 	return 0;
414 }
415 
416 static void amd_cache_gart(void)
417 {
418 	u16 i;
419 
420 	if (!amd_nb_has_feature(AMD_NB_GART))
421 		return;
422 
423 	flush_words = kmalloc_array(amd_northbridges.num, sizeof(u32), GFP_KERNEL);
424 	if (!flush_words) {
425 		amd_northbridges.flags &= ~AMD_NB_GART;
426 		pr_notice("Cannot initialize GART flush words, GART support disabled\n");
427 		return;
428 	}
429 
430 	for (i = 0; i != amd_northbridges.num; i++)
431 		pci_read_config_dword(node_to_amd_nb(i)->misc, 0x9c, &flush_words[i]);
432 }
433 
434 void amd_flush_garts(void)
435 {
436 	int flushed, i;
437 	unsigned long flags;
438 	static DEFINE_SPINLOCK(gart_lock);
439 
440 	if (!amd_nb_has_feature(AMD_NB_GART))
441 		return;
442 
443 	/*
444 	 * Avoid races between AGP and IOMMU. In theory it's not needed
445 	 * but I'm not sure if the hardware won't lose flush requests
446 	 * when another is pending. This whole thing is so expensive anyways
447 	 * that it doesn't matter to serialize more. -AK
448 	 */
449 	spin_lock_irqsave(&gart_lock, flags);
450 	flushed = 0;
451 	for (i = 0; i < amd_northbridges.num; i++) {
452 		pci_write_config_dword(node_to_amd_nb(i)->misc, 0x9c,
453 				       flush_words[i] | 1);
454 		flushed++;
455 	}
456 	for (i = 0; i < amd_northbridges.num; i++) {
457 		u32 w;
458 		/* Make sure the hardware actually executed the flush*/
459 		for (;;) {
460 			pci_read_config_dword(node_to_amd_nb(i)->misc,
461 					      0x9c, &w);
462 			if (!(w & 1))
463 				break;
464 			cpu_relax();
465 		}
466 	}
467 	spin_unlock_irqrestore(&gart_lock, flags);
468 	if (!flushed)
469 		pr_notice("nothing to flush?\n");
470 }
471 EXPORT_SYMBOL_GPL(amd_flush_garts);
472 
473 static void __fix_erratum_688(void *info)
474 {
475 #define MSR_AMD64_IC_CFG 0xC0011021
476 
477 	msr_set_bit(MSR_AMD64_IC_CFG, 3);
478 	msr_set_bit(MSR_AMD64_IC_CFG, 14);
479 }
480 
481 /* Apply erratum 688 fix so machines without a BIOS fix work. */
482 static __init void fix_erratum_688(void)
483 {
484 	struct pci_dev *F4;
485 	u32 val;
486 
487 	if (boot_cpu_data.x86 != 0x14)
488 		return;
489 
490 	if (!amd_northbridges.num)
491 		return;
492 
493 	F4 = node_to_amd_nb(0)->link;
494 	if (!F4)
495 		return;
496 
497 	if (pci_read_config_dword(F4, 0x164, &val))
498 		return;
499 
500 	if (val & BIT(2))
501 		return;
502 
503 	on_each_cpu(__fix_erratum_688, NULL, 0);
504 
505 	pr_info("x86/cpu/AMD: CPU erratum 688 worked around\n");
506 }
507 
508 static __init int init_amd_nbs(void)
509 {
510 	amd_cache_northbridges();
511 	amd_cache_gart();
512 
513 	fix_erratum_688();
514 
515 	return 0;
516 }
517 
518 /* This has to go after the PCI subsystem */
519 fs_initcall(init_amd_nbs);
520