bluetooth: controller: Fix unexpected low TX power with FEM connected

[rugeGerritsen]

Solved by setting the default radio output power when enabling Bluetooth. That is, after the FEM is initialized.

Previously the initial default radio output power would be selected as if there was no FEM connected. For example 6 dBm.
Then, when packets are to be transmitted, we would recalculate how much power we would need on the outputting device. That is, 6 dBm minus the FEM gain.

Signed-off-by: Rubin Gerritsen rubin.gerritsen@nordicsemi.no

[NordicBuilder]

Test specification

CI/Jenkins/NRF

• Integration Platforms

CI/Jenkins/integration

Test Module	File based changes	Manually selected	West overwrite
test-fw-nrfconnect-ble	X
test-fw-nrfconnect-ble_samples	X
test-fw-nrfconnect-chip	X
test-fw-nrfconnect-zigbee	X
test-sdk-find-my	X
test-sdk-homekit	X

Detailed information of selected test modules

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[jciupis]

I'd suggest to rephrase the commit message to better reflect the issue being fixed.

Previously the initial default output power would be selected as if there was no FEM connected.
For example, suppose that the application requested 20dBm power at the antenna. Even though
such power could be achievable using the configured front-end module, that power would first
be converted to the maximum output power supported by the SoC, which usually is much lower.
Then, when the device transmitted frames, this decreased power would be treated as the requested
power and divided between the radio and the external PA.

This commit fixes that by setting the default radio output power when enabling Bluetooth,
when the FEM driver is already initialized. This way the controller takes FEM into account in its
initial output power calculation.

[jciupis]

We probably need to mention the issue in known issues and the fix in release notes changelog.

[NordicBuilder]

You can find the documentation preview for this PR at this link. It will be updated about 10 minutes after the documentation build succeeds.

Note: This comment is automatically posted by the Documentation Publishing GitHub Action.

[weeTike]

This also applies to CONFIG_BT_CTLR_TX_PWR so maybe this statement should be generalized a bit. Something like "when setting a default TX power and :kconfig:option:MPSL_FEM is used.". Or both kconfigs could be mentioned.