docs: document new convention for Kconfig board symbols
Boards have been switched to use "default y" and are now listed
in default-configs/*.mak only for convenience.
Document this change and the new possibilities that it allows.
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
diff --git a/docs/devel/kconfig.rst b/docs/devel/kconfig.rst
index ccb9a46..52d4b90 100644
--- a/docs/devel/kconfig.rst
+++ b/docs/devel/kconfig.rst
@@ -211,6 +211,8 @@
config SUN4M
bool
+ default y
+ depends on SPARC && !SPARC64
imply TCX
imply CG3
select CS4231
@@ -228,8 +230,16 @@
directives. A device should be listed under ``select`` if the board
cannot be started at all without it. It should be listed under
``imply`` if (depending on the QEMU command line) the board may or
- may not be started without it. Boards also default to false; they are
- enabled by the ``default-configs/*.mak`` for the target they apply to.
+ may not be started without it. Boards default to true, but also
+ have a ``depends on`` clause to limit them to the appropriate targets.
+ For some targets, not all boards may be supported by hardware
+ virtualization, in which case they also depend on the ``TCG`` symbol,
+ Other symbols that are commonly used as dependencies for boards
+ include libraries (such as ``FDT``) or ``TARGET_BIG_ENDIAN``
+ (possibly negated).
+
+ Boards are listed for convenience in the ``default-configs/*.mak``
+ for the target they apply to.
**internal elements**