On Fri, Feb 2, 2024 at 1:03 AM Bjorn Andersson [off-list ref] wrote:

[snip]

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I believe I missed this part of the discussion, why does this need to be
a platform_device? What does the platform_bus bring that can't be
provided by some other bus?

Does it need to be a platform_device? No, of course not. Does it make
sense for it to be one? Yes, for two reasons:

1. The ATH11K WLAN module is represented on the device tree like a
platform device, we know it's always there and it consumes regulators
from another platform device. The fact it uses PCIe doesn't change the
fact that it is logically a platform device.

Are you referring to the ath11k SNOC (firmware running on co-processor
in the SoC) variant?

Afaict the PCIe-attached ath11k is not represented as a platform_device
in DeviceTree.

My bad. In RB5 it isn't (yet - I want to add it in the power
sequencing series). It is in X13s though[1].

Said platform_device is also not a child under the PCIe bus, so this
would be a different platform_device...

It's the child of the PCIe port node but there's a reason for it to
have the `compatible` property. It's because it's an entity of whose
existence we are aware before the system boots.

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2. The platform bus already provides us with the entire infrastructure
that we'd now need to duplicate (possibly adding bugs) in order to
introduce a "power sequencing bus".

This is a perfectly reasonable desire. Look at our PMICs, they are full
of platform_devices. But through the years it's been said many times,
that this is not a valid or good reason for using platform_devices, and
as a result we have e.g. auxiliary bus.

Ok, so I cannot find this information anywhere (nor any example). Do
you happen to know if the auxiliary bus offers any software node
integration so that the `compatible` property from DT can get
seamlessly mapped to auxiliary device IDs?

Anyway, (please) don't claim that "we need to", when it actually is "we
want to use platform_device because that's more convenient"!

Bart

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[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm64/boot/dts/qcom/sc8280xp-lenovo-thinkpad-x13s.dts#n744