Incorrect chip id in LibGpiodDriver

[HakanL]

Describe the bug

When attempting to open a GPIO chip using the LibGpiodDriver driver for a device (gpio expander) that isn't the built-in device on a Raspberry Pi I'm getting an error that the chip doesn't exist. I believe the issue is that the Id of the chip (which is used when opening a new GpioController for it) is assigned from an index when iterating, instead of the actual id. I'm calling GetAvailableChips and this is the output:

Found GPIO chip: gpiochip0, label pinctrl-rp1  54 lines
Found GPIO chip: gpiochip10, label gpio-brcmstb@107d508500  32 lines
Found GPIO chip: gpiochip11, label gpio-brcmstb@107d517c00  15 lines
Found GPIO chip: gpiochip12, label gpio-brcmstb@107d517c20  6 lines
Found GPIO chip: gpiochip13, label gpio-brcmstb@107d508520  4 lines
Found GPIO chip: gpiochip14, label 0-0040  16 lines
Found GPIO chip: gpiochip15, label mcp23008  8 lines
Found the MCP23008 GPIO expander chip (v2 base board) at id 6
Error in IoManager constructor: Unable to find a chip, error code: 2
System.IO.IOException: Unable to find a chip, error code: 2
   at System.Device.Gpio.Drivers.LibGpiodDriver..ctor(Int32 gpioChip)
   at DMXCore.DMXCore100.RpiIoManager..ctor(ILoggerFactory loggerFactory, IScheduler scheduler) in D:\Projects\DMXCore\100\Software\Shared\IO\RpiIoManager.cs:line 109

The chip I'm trying to access is the MCP23008 which has name gpiochip15, but the reported chipInfo.Id is 6 (its index when iterating, see https://github.com/dotnet/iot/blob/main/src/System.Device.Gpio/System/Device/Gpio/Drivers/LibGpiodDriver.cs#L132 which I believe is incorrect.

If I parse the Name property to get id 15 in the example above then I can access my device.

Steps to reproduce

Try to access a chip where the list of ids isn't sequential (happens on my Raspberry Pi 5).

Expected behavior

The Id of GpioChipInfo should be the correct id, not the index.

Actual behavior

Error: Unable to find a chip, error code: 2

Versions used

System.Device.Gpio 4.0.1 from Nuget

[pgrawehr]

Can you please provide the exact code sequence you're using? Also, you can just provide the chipinfo to the lLibGpiod constructor, in which case there should be no confusion.

Besides all that, you're doing something rather unexpected. Instead of using a LibGpiodDriver around an mcp kernel driver, just use the mcp binding directly.

[HakanL]

Can you please provide the exact code sequence you're using? Also, you can just provide the chipinfo to the lLibGpiod constructor, in which case there should be no confusion.

This is the code I'm using:

var chips = System.Device.Gpio.Drivers.LibGpiodDriver.GetAvailableChips();
foreach (var chipInfo in chips)
{
	// Look for our MCP chip
	if (chipInfo.Label == "mcp23008")
	{
		this.gpioControllerExp = new GpioController(new System.Device.Gpio.Drivers.LibGpiodDriver(chipInfo));
		break;
	}
}

I am providing the chipInfo to the constructor, but the problem is that the constructor is then using chipInfo.Id, which is incorrect (the Id is incorrect when calling the native libgpiod, it is 15 on my hardware, not 6)

Besides all that, you're doing something rather unexpected. Instead of using a LibGpiodDriver around an mcp kernel driver, just use the mcp binding directly.

Perhaps, but I like to have kernel drivers set up for my hardware (this is a custom product using RPi CM4 and CM5) so that it's available to any software, with or without direct I2C MCP23008 support. But the issue is still there, the Id in ChipInfo is not correct, the same issue would exist if I wanted to use gpiochip14 in my hardware for example. Also the chip ids are different (different i2c bus ids) if I'm using a Raspberry Pi CM4, and I want to be able to support both by just scanning for the mcp23008.

[pgrawehr]

I am providing the chipInfo to the constructor, but the problem is that the constructor is then using chipInfo.Id, which is incorrect

I'll have a look at that later.

But the issue is still there, the Id in ChipInfo is not correct...

No, that doesn't matter in that case. If you use the MCP23008 binding, you don't need the libgpiod driver at all, and also no chipinfo instance, as the binding itself acts as the gpio driver.

[HakanL]

Ok, yeah, I guess if everything is going via the first ChipInfo (including accessing the I2C bus for the MCP23008) then you're correct that it won't matter if the Id is wrong for the "other" chips in the system if you aren't using them. But that doesn't it make it correct either :)