1 // SPDX-License-Identifier: GPL-2.0
2 /*
3  * Primary to Sideband (P2SB) bridge access support
4  *
5  * Copyright (c) 2017, 2021-2022 Intel Corporation.
6  *
7  * Authors: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
8  *	    Jonathan Yong <jonathan.yong@intel.com>
9  */
10 
11 #include <linux/bits.h>
12 #include <linux/export.h>
13 #include <linux/pci.h>
14 #include <linux/platform_data/x86/p2sb.h>
15 
16 #include <asm/cpu_device_id.h>
17 #include <asm/intel-family.h>
18 
19 #define P2SBC			0xe0
20 #define P2SBC_HIDE		BIT(8)
21 
22 #define P2SB_DEVFN_DEFAULT	PCI_DEVFN(31, 1)
23 
24 static const struct x86_cpu_id p2sb_cpu_ids[] = {
25 	X86_MATCH_INTEL_FAM6_MODEL(ATOM_GOLDMONT,	PCI_DEVFN(13, 0)),
26 	{}
27 };
28 
p2sb_get_devfn(unsigned int * devfn)29 static int p2sb_get_devfn(unsigned int *devfn)
30 {
31 	unsigned int fn = P2SB_DEVFN_DEFAULT;
32 	const struct x86_cpu_id *id;
33 
34 	id = x86_match_cpu(p2sb_cpu_ids);
35 	if (id)
36 		fn = (unsigned int)id->driver_data;
37 
38 	*devfn = fn;
39 	return 0;
40 }
41 
42 /* Copy resource from the first BAR of the device in question */
p2sb_read_bar0(struct pci_dev * pdev,struct resource * mem)43 static int p2sb_read_bar0(struct pci_dev *pdev, struct resource *mem)
44 {
45 	struct resource *bar0 = &pdev->resource[0];
46 
47 	/* Make sure we have no dangling pointers in the output */
48 	memset(mem, 0, sizeof(*mem));
49 
50 	/*
51 	 * We copy only selected fields from the original resource.
52 	 * Because a PCI device will be removed soon, we may not use
53 	 * any allocated data, hence we may not copy any pointers.
54 	 */
55 	mem->start = bar0->start;
56 	mem->end = bar0->end;
57 	mem->flags = bar0->flags;
58 	mem->desc = bar0->desc;
59 
60 	return 0;
61 }
62 
p2sb_scan_and_read(struct pci_bus * bus,unsigned int devfn,struct resource * mem)63 static int p2sb_scan_and_read(struct pci_bus *bus, unsigned int devfn, struct resource *mem)
64 {
65 	struct pci_dev *pdev;
66 	int ret;
67 
68 	pdev = pci_scan_single_device(bus, devfn);
69 	if (!pdev)
70 		return -ENODEV;
71 
72 	ret = p2sb_read_bar0(pdev, mem);
73 
74 	pci_stop_and_remove_bus_device(pdev);
75 	return ret;
76 }
77 
78 /**
79  * p2sb_bar - Get Primary to Sideband (P2SB) bridge device BAR
80  * @bus: PCI bus to communicate with
81  * @devfn: PCI slot and function to communicate with
82  * @mem: memory resource to be filled in
83  *
84  * The BIOS prevents the P2SB device from being enumerated by the PCI
85  * subsystem, so we need to unhide and hide it back to lookup the BAR.
86  *
87  * if @bus is NULL, the bus 0 in domain 0 will be used.
88  * If @devfn is 0, it will be replaced by devfn of the P2SB device.
89  *
90  * Caller must provide a valid pointer to @mem.
91  *
92  * Locking is handled by pci_rescan_remove_lock mutex.
93  *
94  * Return:
95  * 0 on success or appropriate errno value on error.
96  */
p2sb_bar(struct pci_bus * bus,unsigned int devfn,struct resource * mem)97 int p2sb_bar(struct pci_bus *bus, unsigned int devfn, struct resource *mem)
98 {
99 	struct pci_dev *pdev_p2sb;
100 	unsigned int devfn_p2sb;
101 	u32 value = P2SBC_HIDE;
102 	int ret;
103 
104 	/* Get devfn for P2SB device itself */
105 	ret = p2sb_get_devfn(&devfn_p2sb);
106 	if (ret)
107 		return ret;
108 
109 	/* if @bus is NULL, use bus 0 in domain 0 */
110 	bus = bus ?: pci_find_bus(0, 0);
111 
112 	/*
113 	 * Prevent concurrent PCI bus scan from seeing the P2SB device and
114 	 * removing via sysfs while it is temporarily exposed.
115 	 */
116 	pci_lock_rescan_remove();
117 
118 	/* Unhide the P2SB device, if needed */
119 	pci_bus_read_config_dword(bus, devfn_p2sb, P2SBC, &value);
120 	if (value & P2SBC_HIDE)
121 		pci_bus_write_config_dword(bus, devfn_p2sb, P2SBC, 0);
122 
123 	pdev_p2sb = pci_scan_single_device(bus, devfn_p2sb);
124 	if (devfn)
125 		ret = p2sb_scan_and_read(bus, devfn, mem);
126 	else
127 		ret = p2sb_read_bar0(pdev_p2sb, mem);
128 	pci_stop_and_remove_bus_device(pdev_p2sb);
129 
130 	/* Hide the P2SB device, if it was hidden */
131 	if (value & P2SBC_HIDE)
132 		pci_bus_write_config_dword(bus, devfn_p2sb, P2SBC, P2SBC_HIDE);
133 
134 	pci_unlock_rescan_remove();
135 
136 	if (ret)
137 		return ret;
138 
139 	if (mem->flags == 0)
140 		return -ENODEV;
141 
142 	return 0;
143 }
144 EXPORT_SYMBOL_GPL(p2sb_bar);
145