Re: Add a SSDT ACPI description to recognize my I2C device connected via SMBus

[Mika Westerberg <mika.westerberg@linux.intel.com>]

Hi,

On Thu, Sep 23, 2021 at 04:17:13PM +0200, Florian Eckert wrote:
> I am working wit OpenWrt which has recently switched the kernel version
> from 5.4 to 5.10 on x86 Target [1] in its master branch.
> 
> I am using a APU3 board from PC-Engine [2].
> 
> The APU3 board has an SMBus [3] device (Intel PIIX4 and compatible
> (ATI/AMD/Serverworks/Broadcom/SMSC) to communicate with additional connected
> I2C devices.
> 
> On This SMBus there is a IO expander from microchip connect [4] via the
> SMBus (i2c).
> I used this microchip IO expander to control additional LEDs, as the APU3
> only has 3.
> 
> So far, everything has worked fine, because I had wirten a platform device
> for this.
> Everything was recognized and compiled cleanly and I could control the LEDs
> from the user-land.
> 
> Due to the following change [5] between 5.4 and 5.10 by removing the
> platform data support in
> the IO expander mcp23s08, my plaform device does not compile anymore,
> I can no longer use the platform device pattern for this kind of device.
> 
> The only possibility I can think of now is to make this device known
> to the kernel via a dynamic ACPI SSDT table. I have already tried various
> things but I can't get the driver [4] to feel responsible for this device.
> 
> I have used the following links that were provided by "Andy Shevchenko" to
> me
> to understand the concept begind ACPI SSDT handling. Thanks for that.
> 
> https://connect.linaro.org/resources/lvc21f/lvc21f-304/
> https://www.youtube.com/watch?v=nlKjUAv3RL0&ab_channel=OSDNConf
> https://stackoverflow.com/questions/65727454/
> https://stackoverflow.com/questions/60105101/
> https://stackoverflow.com/questions/54768841/
> https://stackoverflow.com/questions/46095840/
> https://github.com/westeri/meta-acpi/tree/master/recipes-bsp/acpi-tables/samples/
> 
> This is my aml file that I tried with. It loads but nothing happens.
> 
> DefinitionBlock ("mcp23s08.aml", "SSDT", 5, "", "IO", 2)
> {
>     External (\_SB.PCI0.SBUS, DeviceObj)
> 
>     Device (\_SB.PCI0.SBUS.BUS0)
>     {
>         Name (_CID, "smbus")
>         NAME (_ADR, Zero)
>         Device (PIN)
>         {
>             Name (_HID, "PRP0001")
>             Name (_DDN, "io expander")
>             Name (_CRS, ResourceTemplate () {
>                 I2cSerialBus (
>                     0x24,                   // Bus address
>                     ControllerInitiated,    // Don't care
>                     400000,                 // Fast mode (400 kHz)
>                     AddressingMode7Bit,     // 7-bit addressing
>                     "\\_SB.PCI0.SBUS.BUS0", // I2C host controller
>                     0                       // Must be 0
>                 )
>             })
> 
>             Name (_DSD, Package () {
>                 ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
>                 Package () {
>                     Package () { "compatible", Package () {
> "microchip,mcp23017" } },
>                 }
>             })
>         }
>     }
> }
> 
> In Coreboot the SMBus named SBUS and is on address 0x0014000 [7].
> 
> But I'm not sure if that's right at all.
> Somehow I don't understand how the io expander is connected to SMBus.
> According to my research, however, it should fit.
> 
> The SMBus device driver i2c-piix4 creates 3 I2C devices:
> ls -la /sys/bus/i2c/devices/
> ../../../devices/pci0000:00/0000:00:14.0/i2c-0 (SMBus PIIX4 adapter port 0
> at 0b00)
> ../../../devices/pci0000:00/0000:00:14.0/i2c-1 (SMBus PIIX4 adapter port 2
> at 0b00)
> ../../../devices/pci0000:00/0000:00:14.0/i2c-2 (SMBus PIIX4 adapter port 1
> at 0b20)
> 
> 
> The mcp23s08 is connected to the i2c-0 with address 0x24
> 
> Therefore I believe the following applies
> 
> +------+    +------+
> | PCI0 |--->| SMB0 |--> i2c client A (0x24)
> |      |    |      |
> +------+    +------+
> 
> 
> I have enabled the following kernel config parameters for ACPI SSDT:
> CONFIG_ACPI_CUSTOM_METHOD
> CONFIG_CONFIGFS_FS
> CONFIG_ACPI_CONFIGFS
> CONFIG_ACPI_DEBUG

How do you load the SSDT? Via initrd or something else? You may need to
enable CONFIG_ACPI_TABLE_UPGRADE too. Also do you see in dmesg that the
SSDT is loaded?

Then I suggest checking the below attributes:

 ../../../devices/pci0000:00/0000:00:14.0/firmware_node/path
 ../../../devices/pci0000:00/0000:00:14.0/i2c-0/firmware_node/path