docs/misra: deviate deliberately unused labels

The labels marked with __maybe_unused are either used only
in certain build configurations or deliberately unused.
See the justification in docs/misra/deviations.rst.

No functional changes.

Signed-off-by: Nicola Vetrini <nicola.vetrini@bugseng.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>

automation/eclair_analysis/ECLAIR/deviations.ecl

@@ -37,6 +37,10 @@ removed by the compiler, the resulting slowdown is negligible."
 -config=MC3R1.R2.2,reports+={disapplied,"any()"}
 -doc_end
 
+-doc_begin="Some labels are unused in certain build configurations, or are deliberately marked as unused, so that the compiler is entitled to remove them."
+-config=MC3R1.R2.6,reports+={deliberate, "any_area(text(^.*__maybe_unused.*$))"}
+-doc_end
+
 #
 # Series 3.
 #

docs/misra/deviations.rst

@@ -73,6 +73,14 @@ Deviations related to MISRA C:2012 Rules:
        resulting slowdown is negligible.
      - Project-wide deviation, tagged as `disapplied` for ECLAIR.
 
+   * - R2.6
+     - Labels deliberately marked as unused trough the pseudo-attribute
+       `__maybe_unused` are either the result of them not being in certain build
+       configurations, or as a deliberate practice (e.g., `unimplemented_insn`).
+       Given that the compiler is then entitled to remove them, the presence of
+       such labels poses no risks.
+     - Tagged as `deliberate` for ECLAIR.
+
    * - R3.1
      - Comments starting with '/\*' and containing hyperlinks are safe as they
        are not instances of commented-out code.