Makefile.features: location is not relevant for all features

[biboc]

In #2918, we've observed that the features written in board/XXX/Makefile.features is not always related to the board but mainly to the cpu.
I think that two Makefile.features should exist. For instance, boards/samr21-xpro/Makefile.features and cpu/samd21/Makefile.features

Most of those features (below) depends on the cpu and not the board.
FEATURES_PROVIDED += transceiver
FEATURES_PROVIDED += periph_gpio
FEATURES_PROVIDED += periph_spi
FEATURES_PROVIDED += cpp
FEATURES_PROVIDED += periph_timer
FEATURES_PROVIDED += periph_uart
FEATURES_PROVIDED += periph_i2c
FEATURES_PROVIDED += periph_rtc
FEATURES_PROVIDED += periph_rtt
FEATURES_PROVIDED += periph_cpuid
FEATURES_MCU_GROUP = cortex_m0

Then, FEATURES_CONFLICT will be added in one of the two files according to the reason of the conflict.

[Kijewski]

Makefile.buildtests:225 and Makefile.include:287 are the relevant lines that pull in $(RIOTBOARD)/$(BOARD)/Makefile.features. 👍 for adding $(RIOTCPU)/$(CPU)/Makefile.features.

[biboc]

Ok great! :-)

[Kijewski]

I found a problem with this solution: In Makefile.buildtests we don't know the CPU of a BOARD. So the BOARD's Makefile.features would need to CPU's Makefile.features. Does someone see a problem with that solution?

[biboc]

@Kijewski, I didn't get your solution. Could you provide an example please?

[OlegHahm]

@Kijewski, ping!

[cgundogan]

@Kijewski ping ping

[Kijewski]

Pong, pong, pong.

boards/msba2/Makefile.features imports boards/msba2-common/Makefile.features imports boards/msba2-common/Makefile.features import cpu/lpc2387/Makefile.features import cpu/arm7_common/Makefile.features.

Rationale: Makefile.buildtests does not know MSB-A2's CPU.

[kYc0o]

@Kijewski any news?

[miri64]

Why was this marked as a known issue. Doesn't seem like a bug to me...

[pyropeter]

While working on #6162 (Rust support) we stumbled upon this issue. The solution provided by @Kijewski seems to be reasonable.

We tried to add a feature-flag for Rust support. Since the support depends on the cpu architecture, we added FEATURES_PROVIDED += rust_support to cpu/native/Makefile.features (and others). This works fine regarding the unsupported feature warning displayed when building code for an unsupported board. But this does not work as expected as far as the info-boards-supported target is concerned. As @Kijewski explained, this is caused by the board_missing_features function in Makefile.buildtests. It does not include cpu/$cpu/Makefile.features. This is not easy to fix because the CPU of a certain board is not known in that function.

[pyropeter]

Hello?

[kaspar030]

Doesn't seem like a bug to me...

This is a bug, because edit a cpu's edit Makefile.features is currently not considered for "make info-boards-supported".
This doesn't manifest, as all Makefile.features within boards only define periph_pm, which is currently not correctly used anywhere.

[kaspar030]

Fixed by #7880.