tjh.dev
Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
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linux
1Kernel driver i2c-i801
2
3Supported adapters:
4 * Intel 82801AA and 82801AB (ICH and ICH0 - part of the
5 '810' and '810E' chipsets)
6 * Intel 82801BA (ICH2 - part of the '815E' chipset)
7 * Intel 82801CA/CAM (ICH3)
8 * Intel 82801DB (ICH4) (HW PEC supported)
9 * Intel 82801EB/ER (ICH5) (HW PEC supported)
10 * Intel 6300ESB
11 * Intel 82801FB/FR/FW/FRW (ICH6)
12 * Intel 82801G (ICH7)
13 * Intel 631xESB/632xESB (ESB2)
14 * Intel 82801H (ICH8)
15 * Intel 82801I (ICH9)
16 * Intel EP80579 (Tolapai)
17 * Intel 82801JI (ICH10)
18 * Intel PCH
19 Datasheets: Publicly available at the Intel website
20
21Authors:
22 Mark Studebaker <mdsxyz123@yahoo.com>
23 Jean Delvare <khali@linux-fr.org>
24
25
26Module Parameters
27-----------------
28
29None.
30
31
32Description
33-----------
34
35The ICH (properly known as the 82801AA), ICH0 (82801AB), ICH2 (82801BA),
36ICH3 (82801CA/CAM) and later devices (PCH) are Intel chips that are a part of
37Intel's '810' chipset for Celeron-based PCs, '810E' chipset for
38Pentium-based PCs, '815E' chipset, and others.
39
40The ICH chips contain at least SEVEN separate PCI functions in TWO logical
41PCI devices. An output of lspci will show something similar to the
42following:
43
44 00:1e.0 PCI bridge: Intel Corporation: Unknown device 2418 (rev 01)
45 00:1f.0 ISA bridge: Intel Corporation: Unknown device 2410 (rev 01)
46 00:1f.1 IDE interface: Intel Corporation: Unknown device 2411 (rev 01)
47 00:1f.2 USB Controller: Intel Corporation: Unknown device 2412 (rev 01)
48 00:1f.3 Unknown class [0c05]: Intel Corporation: Unknown device 2413 (rev 01)
49
50The SMBus controller is function 3 in device 1f. Class 0c05 is SMBus Serial
51Controller.
52
53The ICH chips are quite similar to Intel's PIIX4 chip, at least in the
54SMBus controller.
55
56
57Process Call Support
58--------------------
59
60Not supported.
61
62
63I2C Block Read Support
64----------------------
65
66I2C block read is supported on the 82801EB (ICH5) and later chips.
67
68
69SMBus 2.0 Support
70-----------------
71
72The 82801DB (ICH4) and later chips support several SMBus 2.0 features.
73
74
75Hidden ICH SMBus
76----------------
77
78If your system has an Intel ICH south bridge, but you do NOT see the
79SMBus device at 00:1f.3 in lspci, and you can't figure out any way in the
80BIOS to enable it, it means it has been hidden by the BIOS code. Asus is
81well known for first doing this on their P4B motherboard, and many other
82boards after that. Some vendor machines are affected as well.
83
84The first thing to try is the "i2c_ec" ACPI driver. It could be that the
85SMBus was hidden on purpose because it'll be driven by ACPI. If the
86i2c_ec driver works for you, just forget about the i2c-i801 driver and
87don't try to unhide the ICH SMBus. Even if i2c_ec doesn't work, you
88better make sure that the SMBus isn't used by the ACPI code. Try loading
89the "fan" and "thermal" drivers, and check in /proc/acpi/fan and
90/proc/acpi/thermal_zone. If you find anything there, it's likely that
91the ACPI is accessing the SMBus and it's safer not to unhide it. Only
92once you are certain that ACPI isn't using the SMBus, you can attempt
93to unhide it.
94
95In order to unhide the SMBus, we need to change the value of a PCI
96register before the kernel enumerates the PCI devices. This is done in
97drivers/pci/quirks.c, where all affected boards must be listed (see
98function asus_hides_smbus_hostbridge.) If the SMBus device is missing,
99and you think there's something interesting on the SMBus (e.g. a
100hardware monitoring chip), you need to add your board to the list.
101
102The motherboard is identified using the subvendor and subdevice IDs of the
103host bridge PCI device. Get yours with "lspci -n -v -s 00:00.0":
104
10500:00.0 Class 0600: 8086:2570 (rev 02)
106 Subsystem: 1043:80f2
107 Flags: bus master, fast devsel, latency 0
108 Memory at fc000000 (32-bit, prefetchable) [size=32M]
109 Capabilities: [e4] #09 [2106]
110 Capabilities: [a0] AGP version 3.0
111
112Here the host bridge ID is 2570 (82865G/PE/P), the subvendor ID is 1043
113(Asus) and the subdevice ID is 80f2 (P4P800-X). You can find the symbolic
114names for the bridge ID and the subvendor ID in include/linux/pci_ids.h,
115and then add a case for your subdevice ID at the right place in
116drivers/pci/quirks.c. Then please give it very good testing, to make sure
117that the unhidden SMBus doesn't conflict with e.g. ACPI.
118
119If it works, proves useful (i.e. there are usable chips on the SMBus)
120and seems safe, please submit a patch for inclusion into the kernel.
121
122Note: There's a useful script in lm_sensors 2.10.2 and later, named
123unhide_ICH_SMBus (in prog/hotplug), which uses the fakephp driver to
124temporarily unhide the SMBus without having to patch and recompile your
125kernel. It's very convenient if you just want to check if there's
126anything interesting on your hidden ICH SMBus.
127
128
129**********************
130The lm_sensors project gratefully acknowledges the support of Texas
131Instruments in the initial development of this driver.
132
133The lm_sensors project gratefully acknowledges the support of Intel in the
134development of SMBus 2.0 / ICH4 features of this driver.