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docs: i2c: piix4: Add ACPI section
Provide information how to reference I2C busses created by the PIIX4
chip driver from the ACPI code.
Signed-off-by: Konstantin Aladyshev <aladyshev22@gmail.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Bagas Sanjaya <bagasdotme@gmail.com>
Signed-off-by: Andi Shyti <andi.shyti@kernel.org>
authored by
Konstantin Aladyshev
and committed by
Andi Shyti
1922bc24
c366be72
+63
+63
Documentation/i2c/busses/i2c-piix4.rst
+63
Documentation/i2c/busses/i2c-piix4.rst
···
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Thinkpad laptops, but desktop systems may also be affected. We have no list
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of all affected systems, so the only safe solution was to prevent access to
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the SMBus on all IBM systems (detected using DMI data.)
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Description in the ACPI code
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----------------------------
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Device driver for the PIIX4 chip creates a separate I2C bus for each of its
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ports::
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$ i2cdetect -l
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...
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i2c-7 unknown SMBus PIIX4 adapter port 0 at 0b00 N/A
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i2c-8 unknown SMBus PIIX4 adapter port 2 at 0b00 N/A
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i2c-9 unknown SMBus PIIX4 adapter port 1 at 0b20 N/A
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...
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Therefore if you want to access one of these busses in the ACPI code, port
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subdevices are needed to be declared inside the PIIX device::
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Scope (\_SB_.PCI0.SMBS)
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{
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Name (_ADR, 0x00140000)
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Device (SMB0) {
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Name (_ADR, 0)
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}
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Device (SMB1) {
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Name (_ADR, 1)
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}
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Device (SMB2) {
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Name (_ADR, 2)
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}
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}
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If this is not the case for your UEFI firmware and you don't have access to the
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source code, you can use ACPI SSDT Overlays to provide the missing parts. Just
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keep in mind that in this case you would need to load your extra SSDT table
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before the piix4 driver starts, i.e. you should provide SSDT via initrd or EFI
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variable methods and not via configfs.
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As an example of usage here is the ACPI snippet code that would assign jc42
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driver to the 0x1C device on the I2C bus created by the PIIX port 0::
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Device (JC42) {
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Name (_HID, "PRP0001")
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Name (_DDN, "JC42 Temperature sensor")
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Name (_CRS, ResourceTemplate () {
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I2cSerialBusV2 (
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0x001c,
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ControllerInitiated,
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100000,
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AddressingMode7Bit,
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"\\_SB.PCI0.SMBS.SMB0",
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0
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)
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})
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Name (_DSD, Package () {
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ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
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Package () {
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Package () { "compatible", Package() { "jedec,jc-42.4-temp" } },
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}
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})
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}