[Skiboot] [PATCH 4/6] hw/npu2, platform: Add NPU2 platform device detection callback

[Alistair Popple]

> Move the existing I2C-based presence detection for OpenCAPI devices on
> Zaius/ZZ into common code, which we use by default for platforms which do
> not define a callback. Clean up the use of the ibm,npu-link-type property,
> which will now be exposed solely for debugging and not consumed internally.

<snip>

> +/*
> + * A default presence detection implementation for platforms like ZZ and Zaius
> + * that don't provide their own. Assumes all devices found will be OpenCAPI.
> + */
> +static void i2c_presence_detect(struct npu2 *npu)
> +{
> +	struct npu2_dev *dev;
> +	for (int i = 0; i < npu->total_devices; i++) {
> +		dev = &npu->devices[i];
> +		if (platform.ocapi->force_presence ||
> +		    _i2c_presence_detect(dev))
> +			dev->type = NPU2_DEV_TYPE_OPENCAPI;
> +		else
> +			dev->type = NPU2_DEV_TYPE_UNKNOWN;

What are the chances of i2c detection working on unknown platforms? We should
really only default to something if there is a reasonable expectation that it
will work correctly. If not we should default to setting everything to
NPU2_DEV_TYPE_UNKNOWN and have the ZZ and Zaius platforms set
i2c_presence_detect() as their npu2_device_detect callback.

- Alistair