Enforce DEFAULTTUNE across all platforms/architectures/BSPs

Deployed.

Update:

As more discussions and emails come-in on the ML, it becomes clear that:

• We will need a medium and a high compiler-setting for ARM 32bit.

  • This may correspond with the discussed distribution profiles (headless, graphical) that are being discussed. Aka headless = medium , graphical = high

  • The high profile will include the armv7ve tuning (virtualization extensions) resulting in the requirement of >= cortex-15

  • The medium profile will include the armv7-a tuning (no virtualization extensions) resulting in the requirement of >= cortex-a8

  • E.g.:

    • High compiler setting: -march=armv7ve -marm -mfpu=neon-vfpv4  -mfloat-abi=hard

    • Medium compiler setting: -march=armv7-a -mfpu=neon  -mfloat-abi=hard

  • The high profile is similar to the capabilities for aarch64 in 32bit mode

  • The medium profile is very compatible to a broad range of ARM 32bit cores

• We will have one tuning for AARCH64

  • this is "-march=armv8-a"

  • As a distro, we will not apply tunes to specific core types (cortex-a57.cortex-a53).

    • This can be done in your own build w/o issues (we will document)

• We will have one tuning for qemux86_64/intel-core-i7

  • Which exact tuning is still to be decided (have to try out qemu modifications)

  • likely: -m64 -march=corei7 -mfpmath=sse -msse4.2

Sure, things change over time, but a reasonable choice will last for quite some time.

IMHO even if we deprecate porter after DD, the 'common' set of flags  will stay as long as we use ARM 32bit.

To come to a good conclusion we should answer these:
**

• do we need virtualization extensions on ARM 32bit / armv7-a ?

• do we need vfpv4 optimizations ?

• are there reasons to exclude vfpv4 ?

• what CPU's do we expect in the headless profile (cortex-a8 / a9 / a15 / ?? )

Once we have that, the choice can be made.

Thx Jan-Simon for this summary.

My $0.02: the definitions will probably change from time to time. For example, Porter board will not be officially supported after DD so that may lead to some adjustments in the "ARM 32bits High profile". The same could occur if we add a new board.

See https://docs.google.com/presentation/d/1_VSGfheItufCCP_rbGBDg3-2miCyh02-yZva6m8cyUE/edit?usp=sharing