platform_device: better support builtin boilerplate avoidance

We have macros that help reduce the boilerplate for modules
that register with no extra init/exit complexity other than the
most standard use case.  However we see an increasing number of
non-modular drivers using these modular_driver() type register
functions.

There are several downsides to this:
1) The code can appear modular to a reader of the code, and they
   won't know if the code really is modular without checking the
   Makefile and Kconfig to see if compilation is governed by a
   bool or tristate.
2) Coders of drivers may be tempted to code up an __exit function
   that is never used, just in order to satisfy the required three
   args of the modular registration function.
3) Non-modular code ends up including the <module.h> which increases
   CPP overhead that they don't need.
4) It hinders us from performing better separation of the module
   init code and the generic init code.

Here we introduce similar macros, with the mapping from module_driver
to builtin_driver and similar, so that simple changes of:

  module_platform_driver()       --->  builtin_platform_driver()
  module_platform_driver_probe() --->  builtin_platform_driver_probe().

can help us avoid #3 above, without having to code up the same
__init functions and device_initcall() boilerplate.

For non modular code, module_init becomes __initcall.  But direct use
of __initcall is discouraged, vs. one of the priority categorized
subgroups.  As __initcall gets mapped onto device_initcall, our
use of device_initcall directly in this change means that the
runtime impact is zero -- drivers will remain at level 6 in the
initcall ordering.

Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>

1 files changed, 22 insertions, 0 deletions

diff --git a/include/linux/device.h b/include/linux/device.h
index 6558af90c8fe..c2d6167cb4a3 100644
--- a/include/linux/device.h
+++ b/include/linux/device.h
@@ -1269,4 +1269,26 @@ static void __exit __driver##_exit(void) \
 } \
 module_exit(__driver##_exit);
 
+/**
+ * builtin_driver() - Helper macro for drivers that don't do anything
+ * special in init and have no exit. This eliminates some boilerplate.
+ * Each driver may only use this macro once, and calling it replaces
+ * device_initcall (or in some cases, the legacy __initcall).  This is
+ * meant to be a direct parallel of module_driver() above but without
+ * the __exit stuff that is not used for builtin cases.
+ *
+ * @__driver: driver name
+ * @__register: register function for this driver type
+ * @...: Additional arguments to be passed to __register
+ *
+ * Use this macro to construct bus specific macros for registering
+ * drivers, and do not use it on its own.
+ */
+#define builtin_driver(__driver, __register, ...) \
+static int __init __driver##_init(void) \
+{ \
+	return __register(&(__driver) , ##__VA_ARGS__); \
+} \
+device_initcall(__driver##_init);
+
 #endif /* _DEVICE_H_ */