xtensa: add XIP kernel support

XIP (eXecute In Place) kernel image is the image that can be run
directly from ROM, using RAM only for writable data.

XIP xtensa kernel differs from regular xtensa kernel in the following
ways:
- it has exception/IRQ vectors merged into text section. No vectors
  relocation takes place at kernel startup.
- .data/.bss location must be specified in the kernel configuration,
  its content is copied there in the _startup function.
- .init.text is merged with the rest of text and is executed from ROM.
- when MMU is used the virtual address where the kernel will be mapped
  must be specified in the kernel configuration. It may be in the KSEG
  or in the KIO, __pa macro is adjusted to be able to handle both.

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

1 files changed, 46 insertions, 2 deletions

diff --git a/arch/xtensa/Kconfig b/arch/xtensa/Kconfig
index ea9f63c7672d..bf492f9e1f75 100644
--- a/arch/xtensa/Kconfig
+++ b/arch/xtensa/Kconfig
@@ -19,8 +19,8 @@ config XTENSA
 	select GENERIC_PCI_IOMAP
 	select GENERIC_SCHED_CLOCK
 	select GENERIC_STRNCPY_FROM_USER if KASAN
-	select HAVE_ARCH_JUMP_LABEL
-	select HAVE_ARCH_KASAN if MMU
+	select HAVE_ARCH_JUMP_LABEL if !XIP_KERNEL
+	select HAVE_ARCH_KASAN if MMU && !XIP_KERNEL
 	select HAVE_ARCH_TRACEHOOK
 	select HAVE_DEBUG_KMEMLEAK
 	select HAVE_DMA_CONTIGUOUS
@@ -299,6 +299,9 @@ config XTENSA_CALIBRATE_CCOUNT
 config SERIAL_CONSOLE
 	def_bool n
 
+config PLATFORM_HAVE_XIP
+	def_bool n
+
 menu "Platform options"
 
 choice
@@ -325,6 +328,7 @@ config XTENSA_PLATFORM_XTFPGA
 	select PLATFORM_WANT_DEFAULT_MEM if !MMU
 	select SERIAL_CONSOLE
 	select XTENSA_CALIBRATE_CCOUNT
+	select PLATFORM_HAVE_XIP
 	help
 	  XTFPGA is the name of Tensilica board family (LX60, LX110, LX200, ML605).
 	  This hardware is capable of running a full Linux distribution.
@@ -478,6 +482,27 @@ config INITIALIZE_XTENSA_MMU_INSIDE_VMLINUX
 
 	  If in doubt, say Y.
 
+config XIP_KERNEL
+	bool "Kernel Execute-In-Place from ROM"
+	depends on PLATFORM_HAVE_XIP
+	help
+	  Execute-In-Place allows the kernel to run from non-volatile storage
+	  directly addressable by the CPU, such as NOR flash. This saves RAM
+	  space since the text section of the kernel is not loaded from flash
+	  to RAM. Read-write sections, such as the data section and stack,
+	  are still copied to RAM. The XIP kernel is not compressed since
+	  it has to run directly from flash, so it will take more space to
+	  store it. The flash address used to link the kernel object files,
+	  and for storing it, is configuration dependent. Therefore, if you
+	  say Y here, you must know the proper physical address where to
+	  store the kernel image depending on your own flash memory usage.
+
+	  Also note that the make target becomes "make xipImage" rather than
+	  "make Image" or "make uImage". The final kernel binary to put in
+	  ROM memory will be arch/xtensa/boot/xipImage.
+
+	  If unsure, say N.
+
 config MEMMAP_CACHEATTR
 	hex "Cache attributes for the memory address space"
 	depends on !MMU
@@ -522,6 +547,16 @@ config KSEG_PADDR
 
 	  If unsure, leave the default value here.
 
+config KERNEL_VIRTUAL_ADDRESS
+	hex "Kernel virtual address"
+	depends on MMU && XIP_KERNEL
+	default 0xd0003000
+	help
+	  This is the virtual address where the XIP kernel is mapped.
+	  XIP kernel may be mapped into KSEG or KIO region, virtual address
+	  provided here must match kernel load address provided in
+	  KERNEL_LOAD_ADDRESS.
+
 config KERNEL_LOAD_ADDRESS
 	hex "Kernel load address"
 	default 0x60003000 if !MMU
@@ -537,12 +572,21 @@ config KERNEL_LOAD_ADDRESS
 config VECTORS_OFFSET
 	hex "Kernel vectors offset"
 	default 0x00003000
+	depends on !XIP_KERNEL
 	help
 	  This is the offset of the kernel image from the relocatable vectors
 	  base.
 
 	  If unsure, leave the default value here.
 
+config XIP_DATA_ADDR
+	hex "XIP kernel data virtual address"
+	depends on XIP_KERNEL
+	default 0x00000000
+	help
+	  This is the virtual address where XIP kernel data is copied.
+	  It must be within KSEG if MMU is used.
+
 config PLATFORM_WANT_DEFAULT_MEM
 	def_bool n