xtensa: add XIP-aware MTD support

Add Kconfig symbol, asm/mtd-xip.h header and define related macros:
xip_cpu_idle, xip_irqpending, xip_currtime and xip_elapsed_since.
Append .xiptext to the vectors when separate vectors are configured
because otherwise they are appended to the data and data may not even be
executable in XIP configuration.
Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>

arch/xtensa/Kconfig

@@ -70,6 +70,9 @@ config ARCH_HAS_ILOG2_U32
 config ARCH_HAS_ILOG2_U64
 	def_bool n
 
+config ARCH_MTD_XIP
+	def_bool y
+
 config NO_IOPORT_MAP
 	def_bool n
 

arch/xtensa/include/asm/mtd-xip.h

+/* SPDX-License-Identifier: GPL-2.0-only */
+
+#ifndef _ASM_MTD_XIP_H
+#define _ASM_MTD_XIP_H
+
+#include <asm/processor.h>
+
+#define xip_irqpending()	(xtensa_get_sr(interrupt) & xtensa_get_sr(intenable))
+#define xip_currtime()		(xtensa_get_sr(ccount))
+#define xip_elapsed_since(x)	((xtensa_get_sr(ccount) - (x)) / 1000) /* should work up to 1GHz */
+#define xip_cpu_idle()		do { asm volatile ("waiti 0"); } while (0)
+
+#endif /* _ASM_MTD_XIP_H */
+

arch/xtensa/include/asm/sections.h

@@ -34,6 +34,10 @@ extern char _SecondaryResetVector_text_start[];
 extern char _SecondaryResetVector_text_end[];
 #endif
 #ifdef CONFIG_XIP_KERNEL
+#ifdef CONFIG_VECTORS_ADDR
+extern char _xip_text_start[];
+extern char _xip_text_end[];
+#endif
 extern char _xip_start[];
 extern char _xip_end[];
 #endif

arch/xtensa/kernel/setup.c

@@ -311,6 +311,9 @@ void __init setup_arch(char **cmdline_p)
 
 	mem_reserve(__pa(_stext), __pa(_end));
 #ifdef CONFIG_XIP_KERNEL
+#ifdef CONFIG_VECTORS_ADDR
+	mem_reserve(__pa(_xip_text_start), __pa(_xip_text_end));
+#endif
 	mem_reserve(__pa(_xip_start), __pa(_xip_end));
 #endif
 

arch/xtensa/kernel/vmlinux.lds.S

@@ -118,6 +118,7 @@ SECTIONS
     SECTION_VECTOR2 (.DoubleExceptionVector.text, DOUBLEEXC_VECTOR_VADDR)
 
     *(.exception.text)
+    *(.xiptext)
 #endif
 
     IRQENTRY_TEXT
@@ -201,6 +202,9 @@ SECTIONS
 		   .DebugInterruptVector.text);
     RELOCATE_ENTRY(_exception_text,
 		   .exception.text);
+#ifdef CONFIG_XIP_KERNEL
+    RELOCATE_ENTRY(_xip_text, .xiptext);
+#endif
 #endif
 #ifdef CONFIG_XIP_KERNEL
     RELOCATE_ENTRY(_xip_data, .data);
@@ -319,7 +323,12 @@ SECTIONS
 		  LAST)
 #undef LAST
 #define LAST .exception.text
-
+  SECTION_VECTOR4 (_xip_text,
+		  .xiptext,
+		  ,
+		  LAST)
+#undef LAST
+#define LAST .xiptext
 #endif
   . = (LOADADDR(LAST) + SIZEOF(LAST) + 3) & ~ 3;