ANDROID: binder: remove 32-bit binder interface.

New devices launching with Android P need to use the 64-bit
binder interface, even on 32-bit SoCs [0].

This change removes the Kconfig option to select the 32-bit
binder interface. We don't think this will affect existing
userspace for the following reasons:
1) The latest Android common tree is 4.14, so we don't
   believe any Android devices are on kernels >4.14.
2) Android devices launch on an LTS release and stick with
   it, so we wouldn't expect devices running on <= 4.14 now
   to upgrade to 4.17 or later. But even if they did, they'd
   rebuild the world (kernel + userspace) anyway.
3) Other userspaces like 'anbox' are already using the
   64-bit interface.

Note that this change doesn't remove the 32-bit UAPI
itself; the reason for that is that Android userspace
always uses the latest UAPI headers from upstream, and
userspace retains 32-bit support for devices that are
upgrading. This will be removed as well in 2-3 years,
at which point we can remove the code from the UAPI
as well.

Finally, this change introduces build errors on archs where
64-bit get_user/put_user is not supported, so make binder
unavailable on m68k (which wouldn't want it anyway).

[0]: https://android-review.googlesource.com/c/platform/build/+/595193Signed-off-by: Martijn Coenen <maco@android.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/android/Kconfig

@@ -10,7 +10,7 @@ if ANDROID
 
 config ANDROID_BINDER_IPC
 	bool "Android Binder IPC Driver"
-	depends on MMU
+	depends on MMU && !M68K
 	default n
 	---help---
 	  Binder is used in Android for both communication between processes,
@@ -32,19 +32,6 @@ config ANDROID_BINDER_DEVICES
 	  created. Each binder device has its own context manager, and is
 	  therefore logically separated from the other devices.
 
-config ANDROID_BINDER_IPC_32BIT
-	bool "Use old (Android 4.4 and earlier) 32-bit binder API"
-	depends on !64BIT && ANDROID_BINDER_IPC
-	default y
-	---help---
-	  The Binder API has been changed to support both 32 and 64bit
-	  applications in a mixed environment.
-
-	  Enable this to support an old 32-bit Android user-space (v4.4 and
-	  earlier).
-
-	  Note that enabling this will break newer Android user-space.
-
 config ANDROID_BINDER_IPC_SELFTEST
 	bool "Android Binder IPC Driver Selftest"
 	depends on ANDROID_BINDER_IPC

drivers/android/binder.c

@@ -72,10 +72,6 @@
 #include <linux/security.h>
 #include <linux/spinlock.h>
 
-#ifdef CONFIG_ANDROID_BINDER_IPC_32BIT
-#define BINDER_IPC_32BIT 1
-#endif
-
 #include <uapi/linux/android/binder.h>
 #include "binder_alloc.h"
 #include "binder_trace.h"