1 .. SPDX-License-Identifier: GPL-2.0
2
3 ========================================
4 ACPI considerations for PCI host bridges
5 ========================================
6
7 The general rule is that the ACPI namespace sh
8 OS might use unless there's another way for th
9
10 For example, there's no standard hardware mech
11 host bridges, so the ACPI namespace must descr
12 method for accessing PCI config space below it
13 the host bridge forwards to PCI (using _CRS),
14 INTx interrupts (using _PRT).
15
16 PCI devices, which are below the host bridge,
17 described via ACPI. The OS can discover them
18 enumeration mechanism, using config accesses t
19 devices and read and size their BARs. However
20 devices if it provides power management or hot
21 or if the device has INTx interrupts connected
22 controllers and a _PRT is needed to describe t
23
24 ACPI resource description is done via _CRS obj
25 namespace [2]. The _CRS is like a generalize
26 _CRS and figure out what resource is being con
27 a driver for the device [3]. That's important
28 can work correctly even on a system with new d
29 The new devices might not do anything, but the
30 resources conflict with them.
31
32 Static tables like MCFG, HPET, ECDT, etc., are
33 reserving address space. The static tables ar
34 know early in boot, before it can parse the AC
35 is defined, an old OS needs to operate correct
36 table. _CRS allows that because it is generic
37 OS; a static table does not.
38
39 If the OS is expected to manage a non-discover
40 ACPI, that device will have a specific _HID/_C
41 driver to bind to it, and the _CRS tells the O
42 device's registers are.
43
44 PCI host bridges are PNP0A03 or PNP0A08 device
45 describe all the address space they consume.
46 they forward down to the PCI bus, as well as r
47 itself that are not forwarded to PCI. The hos
48 things like secondary/subordinate bus register
49 range below the bridge, window registers that
50 These are all device-specific, non-architected
51 PNP0A03/PNP0A08 driver can manage them is via
52 the device-specific details. The host bridge
53 space, since it is consumed by the host bridge
54
55 ACPI defines a Consumer/Producer bit to distin
56 ("Consumer") from the bridge apertures ("Produ
57 BIOSes didn't use that bit correctly. The res
58 spec defines Consumer/Producer only for the Ex
59 descriptors; the bit should be ignored in the
60 Address Space descriptors. Consequently, OSes
61 QWord/DWord/Word descriptors are windows.
62
63 Prior to the addition of Extended Address Spac
64 Consumer/Producer meant there was no way to de
65 the PNP0A03/PNP0A08 device itself. The workar
66 bridge registers (including ECAM space) in PNP
67 With the exception of ECAM, the bridge registe
68 anyway, so the generic PNP0A03/PNP0A08 driver
69 know about it.
70
71 New architectures should be able to use "Consu
72 descriptors in the PNP0A03 device for bridge r
73 although a strict interpretation of [6] might
74 ia64 kernels assume all address space descript
75 Extended Address Space ones, are windows, so i
76 describe bridge registers this way on those ar
77
78 PNP0C02 "motherboard" devices are basically a
79 programming model for them other than "don't u
80 anything else." So a PNP0C02 _CRS should clai
81 (1) not claimed by _CRS under any other device
82 and (2) should not be assigned by the OS to so
83
84 The PCIe spec requires the Enhanced Configurat
85 unless there's a standard firmware interface f
86 ia64 SAL interface [7]. A host bridge consume
87 and converts memory accesses into PCI configur
88 defines the ECAM address space layout and func
89 the address space is device-specific. An ACPI
90 from either the static MCFG table or a _CBA me
91
92 The MCFG table must describe the ECAM space of
93 bridges [8]. Since MCFG is a static table and
94 a _CBA method in the PNP0A03 device describes
95 hot-pluggable host bridge [9]. Note that for
96 address always corresponds to bus 0, even if t
97 (which is reported via _CRS) doesn't start at
98
99
100 [1] ACPI 6.2, sec 6.1:
101 For any device that is on a non-enumerable
102 ISA bus), OSPM enumerates the devices' ide
103 system firmware must supply an _HID object
104 enable OSPM to do that.
105
106 [2] ACPI 6.2, sec 3.7:
107 The OS enumerates motherboard devices simp
108 ACPI Namespace looking for devices with ha
109
110 Each device enumerated by ACPI includes AC
111 ACPI Namespace that report the hardware re
112 occupy [_PRS], an object that reports the
113 used by the device [_CRS], and objects for
114 [_SRS]. The information is used by the Pl
115 configure the devices.
116
117 [3] ACPI 6.2, sec 6.2:
118 OSPM uses device configuration objects to
119 for devices enumerated via ACPI. Device c
120 information about current and possible res
121 relationship between shared resources, and
122 hardware resources.
123
124 When OSPM enumerates a device, it calls _P
125 requirements of the device. It may also c
126 resource settings for the device. Using t
127 Play system determines what resources the
128 sets those resources by calling the device
129
130 In ACPI, devices can consume resources (fo
131 provide resources (for example, a propriet
132 Unless otherwise specified, resources for
133 taken from the nearest matching resource a
134 hierarchy.
135
136 [4] ACPI 6.2, sec 6.4.3.5.1, 2, 3, 4:
137 QWord/DWord/Word Address Space Descriptor
138 General Flags: Bit [0] Ignored
139
140 Extended Address Space Descriptor (.4)
141 General Flags: Bit [0] Consumer/Producer
142
143 * 1 – This device consumes this reso
144 * 0 – This device produces and consu
145
146 [5] ACPI 6.2, sec 19.6.43:
147 ResourceUsage specifies whether the Memory
148 this device (ResourceConsumer) or passed o
149 (ResourceProducer). If nothing is specifi
150 ResourceConsumer is assumed.
151
152 [6] PCI Firmware 3.2, sec 4.1.2:
153 If the operating system does not natively
154 MMCFG region, the MMCFG region must be res
155 address range reported in the MCFG table o
156 4.1.3) must be reserved by declaring a mot
157 systems, the motherboard resource would ap
158 namespace (under \_SB) in a node with a _H
159 the resources in this case should not be c
160 _CRS. The resources can optionally be ret
161 EFIGetMemoryMap as reserved memory but mus
162 ACPI as a motherboard resource.
163
164 [7] PCI Express 4.0, sec 7.2.2:
165 For systems that are PC-compatible, or tha
166 processor-architecture-specific firmware i
167 access to the Configuration Space, the ECA
168 this section.
169
170 [8] PCI Firmware 3.2, sec 4.1.2:
171 The MCFG table is an ACPI table that is us
172 addresses corresponding to the non-hot rem
173 range within a PCI Segment Group available
174 boot. This is required for the PC-compatib
175
176 The MCFG table is only used to communicate
177 corresponding to the PCI Segment Groups av
178 boot.
179
180 [9] PCI Firmware 3.2, sec 4.1.3:
181 The _CBA (Memory mapped Configuration Base
182 an optional ACPI object that returns the 6
183 configuration base address for the hot plu
184 base address returned by _CBA is processor
185 control method evaluates to an Integer.
186
187 This control method appears under a host b
188 method appears under an active host bridge
189 evaluates this structure to identify the m
190 base address corresponding to the PCI Segm
191 range specified in _CRS method. An ACPI na
192 the _CBA method must also contain a corres
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