Introduce MORTSGNA_ARMV7_TUNE to reduce armv7a build variant optionally

It depends on user's needs - and is not a pinned distro decision.

Signed-off-by: Andreas Müller <schnitzeltony@gmail.com>

README

@@ -9,13 +9,31 @@
 
 meta-mortsgna is yet another distribution layer. It is based on Ångström
 distribution  - check https://github.com/Angstrom-distribution/meta-angstrom.
+
 The target of this layer is to build images with the best out-of-the-box
-experience.
+experience and to support developers with helpers for common tasks.
 
 -------------------------------------------------------------------------------
 Layer maintainer: Andreas Müller <schnitzeltony@gmail.com>
 
 
+-------------------------------------------------------------------------------
+Additionally this layer checks the following variable in local.conf:
+
+* MORTSGNA_ARMV7_TUNE:
+  If this variable is set to "1", all armv7a / cortex variants are build as
+  armv7a.
+
+  + Reduce build time/disk-space required when building for multiple machines
+  - Build optimzation (e.g vfp/NEON) is not the best your machine can get
+
+  Rules of thumb:
+  * If you build images for multiple armv7 machines and don't need to tickle
+    the last quarter of your machine's performance:
+    Set MORTSGNA_ARMV7_TUNE="1"
+  * If you are intersted in best optimization for your machine and/or you have
+    a fast build host with lots of disk-space: don't!
+
 -------------------------------------------------------------------------------
 This layer contains the following folders:
 

TODO

@@ -2,7 +2,6 @@ These are tasks are planned:
 
 OE:
 * Introduce security_flags.inc
-* Add an OPTION for local.conf to reduce all armv7a to common tune values
 
 Scripts:
 * get rid of bashisms

conf/distro/include/mortsgna-armv7-tune.inc

@@ -0,0 +1,17 @@
+def armv7_tune_handler(d):
+    tune = d.getVar('DEFAULTTUNE', True)
+    # set MORTSGNA_ARMV7_TUNE="1" in your local.conf to reduce all cortex variants
+    # to common tune value
+    if d.getVar('MORTSGNA_ARMV7_TUNE', True) == '1':
+        features = d.getVar('TUNE_FEATURES', True).split()
+        if 'armv7a' in features or 'armv7ve' in features:
+            tune = 'armv7athf'
+            if 'bigendian' in features:
+                tune += 'b'
+            if 'neon' in features:
+                tune += '-neon'
+        else:
+            tune = d.getVar('DEFAULTTUNE', True)
+
+    return tune
+

conf/distro/include/mortsgna.inc

@@ -33,6 +33,10 @@ ARM_INSTRUCTION_SET_armv4 ?= "arm"
 ARM_INSTRUCTION_SET_armv5 ?= "arm"
 ARM_INSTRUCTION_SET_armv6 ?= "arm"
 
+# set MORTSGNA_ARMV7_TUNE="1" in your local.conf to build armv7athf
+require conf/distro/include/mortsgna-armv7-tune.inc
+DEFAULTTUNE_mortsgna := "${@armv7_tune_handler(d)}"
+
 # use debian style naming
 INHERIT += "debian"