Re: Adding I2C devices to the SMBus (PIIX4) via the ACPI SSDT overlay method

[Andy Shevchenko <andriy.shevchenko@linux.intel.com>]

On Thu, Nov 07, 2024 at 06:51:03PM +0300, Konstantin Aladyshev wrote:
> Hello!
> 
> I'm trying to add I2C devices to I2C/SMBus buses via the ACPI SSDT
> overlay method. I've managed to do it for the I2C buses, but can't get
> it working for the SMBus (PIIX4).

...

> Now I'm trying to add devices to the SMBus bus. Which in my case is
> produced from the i2c_piix4 PCI device:
> ```
> $ lspci -s 00:14.0 -vvvxxx
> 00:14.0 SMBus: Advanced Micro Devices, Inc. [AMD] FCH SMBus Controller (rev 61)
>         Subsystem: Advanced Micro Devices, Inc. [AMD] FCH SMBus Controller
>         Control: I/O+ Mem+ BusMaster- SpecCycle- MemWINV- VGASnoop-
> ParErr- Stepping- SERR- FastB2B- DisINTx+
>         Status: Cap- 66MHz+ UDF- FastB2B- ParErr- DEVSEL=medium
> >TAbort- <TAbort- <MAbort- >SERR- <PERR- INTx-
>         NUMA node: 0
>         IOMMU group: 58
>         Kernel driver in use: piix4_smbus
>         Kernel modules: i2c_piix4, sp5100_tco
> 00: 22 10 0b 79 03 04 20 02 61 00 05 0c 00 00 80 00
> 10: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> 20: 00 00 00 00 00 00 00 00 00 00 00 00 22 10 0b 79
> 30: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> ```
> 
> It is described as simple as this in the system ACPI code:
> ```
> Device (SMBS) // \_SB_.PCI0.SMBS
> {
>     Name (_ADR, 0x00140000)  // _ADR: Address

So, you need to add Device objects here

The driver (drivers/i2c/busses/i2c-piix4.c::1157) has this call:

	acpi_preset_companion(&adap->dev, ACPI_COMPANION(&dev->dev), hw_port_nr);

Means, that the _ADR will be evaluated, but there is none for the ports, only
for the physical device.

So, you need something like this:

	Scope (\_SB_.PCI0.SMBS)
	{
	  Device (SMB1)
	  {
	    Name (_ADR, 0)
	  }
	  Device (SMB1)
	  {
	    Name (_ADR, 1)
	  }
	  Device (SMB2)
	  {
	    Name (_ADR, 2)
	  }
	}


And then refer to the controller (respective port) as, for example,

	\_SB_.PCI0.SMBS.SMB1

in your SSDT. Note, the above _ADR assignments you should also add to SSDT
(better to the same one).

> }
> ```
> And produces several I2C busses to the system:
> ```
> i2c-7   unknown         SMBus PIIX4 adapter port 0 at 0b00      N/A
> i2c-8   unknown         SMBus PIIX4 adapter port 2 at 0b00      N/A
> i2c-9   unknown         SMBus PIIX4 adapter port 1 at 0b20      N/A
> ```
> 
> No matter how I've tried, I can't get to add my custom devices to
> these SMBus buses.
> 
> Apparently just using "\\_SB.PCI0.SMBS" is not enough for this case.
> Maybe I need to somehow create port nodes for this Device? Or maybe it
> is not possible at all with the current piix driver?
> 
> Anyway I've started digging and I've noticed that for the I2C device
> there are two physical_nodes in the sysfs. Where the 'physical_node'
> is a standard folder and 'physical_node1' is a direct link to the
> proper i2c bus:

> Maybe I need to modify ACPI code somehow to create these
> 'physical_nodesX' folders for the relevant i2c-7/8/9 buses?

If you succeed with the above, please add the respective section to
the Documentation/i2c/busses/i2c-piix4.rst and send a patch. It will
be very appreciated!

-- 
With Best Regards,
Andy Shevchenko