xtensa: make secondary reset vector support conditional

Whether xtensa cores start from primary or secondary reset vector is
configurable and may be chosen by board designer or controlled at
runtime. When secondary reset vector is unused its location in memory
may not be writable.
Make secondary reset vector support conditional and don't build and load
secondary reset vector code when it is disabled.

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>

Author: jcmvbkbc

arch/xtensa/Kconfig

@@ -227,6 +227,15 @@ config HOTPLUG_CPU
 
 	  Say N if you want to disable CPU hotplug.
 
+config SECONDARY_RESET_VECTOR
+	bool "Secondary cores use alternative reset vector"
+	default y
+	depends on HAVE_SMP
+	help
+	  Secondary cores may be configured to use alternative reset vector,
+	  or all cores may use primary reset vector.
+	  Say Y here to supply handler for the alternative reset location.
+
 config FAST_SYSCALL_XTENSA
 	bool "Enable fast atomic syscalls"
 	default n

arch/xtensa/kernel/Makefile

@@ -13,7 +13,8 @@ obj-$(CONFIG_MMU) += pci-dma.o
 obj-$(CONFIG_PCI) += pci.o
 obj-$(CONFIG_MODULES) += xtensa_ksyms.o module.o
 obj-$(CONFIG_FUNCTION_TRACER) += mcount.o
-obj-$(CONFIG_SMP) += smp.o mxhead.o
+obj-$(CONFIG_SMP) += smp.o
+obj-$(CONFIG_SECONDARY_RESET_VECTOR) += mxhead.o
 obj-$(CONFIG_XTENSA_VARIANT_HAVE_PERF_EVENTS) += perf_event.o
 obj-$(CONFIG_HAVE_HW_BREAKPOINT) += hw_breakpoint.o
 obj-$(CONFIG_S32C1I_SELFTEST) += s32c1i_selftest.o

arch/xtensa/kernel/setup.c

@@ -349,7 +349,7 @@ void __init setup_arch(char **cmdline_p)
 
 #endif /* CONFIG_VECTORS_ADDR */
 
-#ifdef CONFIG_SMP
+#ifdef CONFIG_SECONDARY_RESET_VECTOR
 	mem_reserve(__pa(_SecondaryResetVector_text_start),
 		    __pa(_SecondaryResetVector_text_end));
 #endif

arch/xtensa/kernel/vmlinux.lds.S

@@ -207,7 +207,7 @@ SECTIONS
     RELOCATE_ENTRY(_xip_data, .data);
     RELOCATE_ENTRY(_xip_init_data, .init.data);
 #endif
-#if defined(CONFIG_SMP)
+#if defined(CONFIG_SECONDARY_RESET_VECTOR)
     RELOCATE_ENTRY(_SecondaryResetVector_text,
 		   .SecondaryResetVector.text);
 #endif
@@ -303,7 +303,7 @@ SECTIONS
 #define LAST .DoubleExceptionVector.text
 
 #endif
-#if defined(CONFIG_SMP)
+#if defined(CONFIG_SECONDARY_RESET_VECTOR)
 
   SECTION_VECTOR4 (_SecondaryResetVector_text,
 		  .SecondaryResetVector.text,