x86: Add i8042 pre-detection hook to x86_platform_ops

Some x86 platforms like Intel MID platforms don't have i8042 controllers,
and i8042 driver's probe to some legacy IO ports may hang the MID
processor. With this hook, i8042 driver can runtime check and skip the
probe when the pretection fail which also saves some probe time

[ hpa note: this is currently a compile-time check, which breaks the
  i386 allyesconfig build.  This patch series thus does fix a regression. ]

Signed-off-by: Feng Tang <feng.tang@intel.com>
LKML-Reference: <1278342202-10973-2-git-send-email-feng.tang@intel.com>
Acked-by: Dmitry Torokhov <dtor@mail.ru>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>

arch/x86/include/asm/x86_init.h

@@ -142,6 +142,7 @@ struct x86_cpuinit_ops {
  * @set_wallclock:		set time back to HW clock
  * @is_untracked_pat_range	exclude from PAT logic
  * @nmi_init			enable NMI on cpus
+ * @i8042_detect		pre-detect if i8042 controller exists
  */
 struct x86_platform_ops {
 	unsigned long (*calibrate_tsc)(void);
@@ -150,6 +151,7 @@ struct x86_platform_ops {
 	void (*iommu_shutdown)(void);
 	bool (*is_untracked_pat_range)(u64 start, u64 end);
 	void (*nmi_init)(void);
+	int (*i8042_detect)(void);
 };
 
 extern struct x86_init_ops x86_init;

arch/x86/kernel/x86_init.c

@@ -86,6 +86,7 @@ struct x86_cpuinit_ops x86_cpuinit __cpuinitdata = {
 };
 
 static void default_nmi_init(void) { };
+static int default_i8042_detect(void) { return 1; };
 
 struct x86_platform_ops x86_platform = {
 	.calibrate_tsc			= native_calibrate_tsc,
@@ -93,7 +94,8 @@ struct x86_platform_ops x86_platform = {
 	.set_wallclock			= mach_set_rtc_mmss,
 	.iommu_shutdown			= iommu_shutdown_noop,
 	.is_untracked_pat_range		= is_ISA_range,
-	.nmi_init			= default_nmi_init
+	.nmi_init			= default_nmi_init,
+	.i8042_detect			= default_i8042_detect
 };
 
 EXPORT_SYMBOL_GPL(x86_platform);