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Subject[PATCH 3/3] i2c: add ACPI support for i2c-piix4
This enables the i2c-piix4 SMBus controller driver to enumerate I2C
slave devices using ACPI. It builds on the related I2C mux device work
in commit 8eb5c87a92c0 ("i2c: add ACPI support for I2C mux ports")

In the i2c-piix4 driver the adapters are enumerated as:
Main SMBus adapter Port 0, Port 2, ..., aux port (i.e., ASF adapter)

However, in the AMD BKDG documentation[1], the implied order of ports is:
Main SMBus adapter Port 0, ASF adapter, Port 2, Port 3, ...

This ordering difference is unfortunate, and we assume that ACPI
developers will use the Linux ordering.

[1] 52740 BIOS and Kernel Developer's Guide (BKDG) for AMD Family 16h
Models 30h-3Fh Processors

Signed-off-by: Andrew Cooks <>
drivers/i2c/busses/i2c-piix4.c | 6 ++++++
1 file changed, 6 insertions(+)

diff --git a/drivers/i2c/busses/i2c-piix4.c b/drivers/i2c/busses/i2c-piix4.c
index 9763241..97eb6ae 100644
--- a/drivers/i2c/busses/i2c-piix4.c
+++ b/drivers/i2c/busses/i2c-piix4.c
@@ -843,6 +843,12 @@ static int piix4_add_adapter(struct pci_dev *dev, unsigned short smba,
/* set up the sysfs linkage to our parent device */
adap->dev.parent = &dev->dev;

+ if (has_acpi_companion(&dev->dev)) {
+ acpi_preset_companion(&adap->dev,
+ ACPI_COMPANION(&dev->dev),
+ piix4_adapter_count++);
+ }
snprintf(adap->name, sizeof(adap->name),
"SMBus PIIX4 adapter%s at %04x", name, smba);

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