kconfig: implement KCONFIG_PROBABILITY for randconfig

Currently the odds to set each symbol is (rounded):
    booleans:   y: 50%          n: 50%
    tristates:  y: 33%  m: 33%  n: 33%

Introduce a KCONFIG_PROBABILITY environment variable to tweak the
probabilities (in percentage), as such:
    KCONFIG_PROBABILITY     y:n split           y:m:n split
    -----------------------------------------------------------------
[1] unset or empty          50  : 50            33  : 33  : 34
[2] N                        N  : 100-N         N/2 : N/2 : 100-N
    N:M                     N+M : 100-(N+M)      N  :  M  : 100-(N+M)
    N:M:L                    N  : 100-N          M  :  L  : 100-(M+L)

[1] The current behaviour is kept as default, for backward compatibility
[2] The solution initially implemented by Peter for Buildroot, see:
    http://git.buildroot.org/buildroot/commit/?id=3435c1afb5

Signed-off-by: Peter Korsgaard <jacmet@uclibc.org>
[yann.morin.1998@free.fr: add to Documentation/]
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>

1 files changed, 27 insertions, 0 deletions

diff --git a/Documentation/kbuild/kconfig.txt b/Documentation/kbuild/kconfig.txt
index dbf746b70553..3f429ed8b3b8 100644
--- a/Documentation/kbuild/kconfig.txt
+++ b/Documentation/kbuild/kconfig.txt
@@ -98,6 +98,33 @@ You can set this to the integer value used to seed the RNG, if you want
 to somehow debug the behaviour of the kconfig parser/frontends.
 If not set, the current time will be used.
 
+KCONFIG_PROBABILITY
+--------------------------------------------------
+This variable can be used to skew the probabilities. This variable can
+be unset or empty, or set to three different formats:
+        KCONFIG_PROBABILITY     y:n split           y:m:n split
+        -----------------------------------------------------------------
+        unset or empty          50  : 50            33  : 33  : 34
+        N                        N  : 100-N         N/2 : N/2 : 100-N
+    [1] N:M                     N+M : 100-(N+M)      N  :  M  : 100-(N+M)
+    [2] N:M:L                    N  : 100-N          M  :  L  : 100-(M+L)
+
+where N, M and L are integers (in base 10) in the range [0,100], and so
+that:
+    [1] N+M is in the range [0,100]
+    [2] M+L is in the range [0,100]
+
+Examples:
+        KCONFIG_PROBABILITY=10
+                10% of booleans will be set to 'y', 90% to 'n'
+                5% of tristates will be set to 'y', 5% to 'm', 90% to 'n'
+        KCONFIG_PROBABILITY=15:25
+                40% of booleans will be set to 'y', 60% to 'n'
+                15% of tristates will be set to 'y', 25% to 'm', 60% to 'n'
+        KCONFIG_PROBABILITY=10:15:15
+                10% of booleans will be set to 'y', 90% to 'n'
+                15% of tristates will be set to 'y', 15% to 'm', 70% to 'n'
+
 ______________________________________________________________________
 Environment variables for 'silentoldconfig'