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Subject[PATCH 4.4 003/135] i2c: piix4: Detect secondary SMBus controller on AMD AM4 chipsets
From: Adam Honse <>

[ Upstream commit f27237c174fd9653033330e4e532cd9d153ce824 ]

The AMD X370 and other AM4 chipsets (A/B/X 3/4/5 parts) and Threadripper
equivalents have a secondary SMBus controller at I/O port address
0x0B20. This bus is used by several manufacturers to control
motherboard RGB lighting via embedded controllers. I have been using
this bus in my OpenRGB project to control the Aura RGB on many
motherboards and ASRock also uses this bus for their Polychrome RGB

I am not aware of any CZ-compatible platforms which do not have the
second SMBus channel. All of AMD's AM4- and Threadripper- series
chipsets that OpenRGB users have tested appear to have this secondary
bus. I also noticed this secondary bus is present on older AMD
platforms including my FM1 home server.

Signed-off-by: Adam Honse <>
Reviewed-by: Jean Delvare <>
Reviewed-by: Sebastian Reichel <>
Tested-by: Sebastian Reichel <>
Signed-off-by: Wolfram Sang <>
Signed-off-by: Sasha Levin <>
drivers/i2c/busses/i2c-piix4.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/i2c/busses/i2c-piix4.c b/drivers/i2c/busses/i2c-piix4.c
index b61db9db3ca5d..c85ac178c4838 100644
--- a/drivers/i2c/busses/i2c-piix4.c
+++ b/drivers/i2c/busses/i2c-piix4.c
@@ -647,7 +647,8 @@ static int piix4_probe(struct pci_dev *dev, const struct pci_device_id *id)

if (dev->vendor == PCI_VENDOR_ID_AMD &&
- dev->device == PCI_DEVICE_ID_AMD_HUDSON2_SMBUS) {
+ (dev->device == PCI_DEVICE_ID_AMD_HUDSON2_SMBUS ||
+ dev->device == PCI_DEVICE_ID_AMD_KERNCZ_SMBUS)) {
retval = piix4_setup_sb800(dev, id, 1);

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