RISC-V: enable XIP

Introduce XIP (eXecute In Place) support for RISC-V platforms.
It allows code to be executed directly from non-volatile storage
directly addressable by the CPU, such as QSPI NOR flash which can
be found on many RISC-V platforms. This makes way for significant
optimization of RAM footprint. The XIP kernel is not compressed
since it has to run directly from flash, so it will occupy more
space on the non-volatile storage. The physical flash address used
to link the kernel object files and for storing it has to be known
at compile time and is represented by a Kconfig option.

XIP on RISC-V will for the time being only work on MMU-enabled
kernels.

Signed-off-by: Vitaly Wool <vitaly.wool@konsulko.com>
[Alex: Rebase on top of "Move kernel mapping outside the linear mapping" ]
Signed-off-by: Alexandre Ghiti <alex@ghiti.fr>
[Palmer: disable XIP for allyesconfig]
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>

2 files changed, 44 insertions, 2 deletions

diff --git a/arch/riscv/include/asm/page.h b/arch/riscv/include/asm/page.h
index f64b61296c0c..e280ba60cb34 100644
--- a/arch/riscv/include/asm/page.h
+++ b/arch/riscv/include/asm/page.h
@@ -93,6 +93,9 @@ extern unsigned long va_pa_offset;
 #ifdef CONFIG_64BIT
 extern unsigned long va_kernel_pa_offset;
 #endif
+#ifdef CONFIG_XIP_KERNEL
+extern unsigned long va_kernel_xip_pa_offset;
+#endif
 extern unsigned long pfn_base;
 #define ARCH_PFN_OFFSET		(pfn_base)
 #else
@@ -107,11 +110,29 @@ extern unsigned long pfn_base;
 extern unsigned long kernel_virt_addr;
 
 #define linear_mapping_pa_to_va(x)	((void *)((unsigned long)(x) + va_pa_offset))
+#ifdef CONFIG_XIP_KERNEL
+#define kernel_mapping_pa_to_va(y)	({						\
+	unsigned long _y = y;								\
+	(_y >= CONFIG_PHYS_RAM_BASE) ?							\
+		(void *)((unsigned long)(_y) + va_kernel_pa_offset + XIP_OFFSET) :	\
+		(void *)((unsigned long)(_y) + va_kernel_xip_pa_offset);		\
+	})
+#else
 #define kernel_mapping_pa_to_va(x)	((void *)((unsigned long)(x) + va_kernel_pa_offset))
+#endif
 #define __pa_to_va_nodebug(x)		linear_mapping_pa_to_va(x)
 
 #define linear_mapping_va_to_pa(x)	((unsigned long)(x) - va_pa_offset)
+#ifdef CONFIG_XIP_KERNEL
+#define kernel_mapping_va_to_pa(y) ({						\
+	unsigned long _y = y;							\
+	(_y < kernel_virt_addr + XIP_OFFSET) ?					\
+		((unsigned long)(_y) - va_kernel_xip_pa_offset) :		\
+		((unsigned long)(_y) - va_kernel_pa_offset - XIP_OFFSET);	\
+	})
+#else
 #define kernel_mapping_va_to_pa(x)	((unsigned long)(x) - va_kernel_pa_offset)
+#endif
 #define __va_to_pa_nodebug(x)	({						\
 	unsigned long _x = x;							\
 	(_x < kernel_virt_addr) ?						\
diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
index 5afda75cc2c3..2f1384e14e31 100644
--- a/arch/riscv/include/asm/pgtable.h
+++ b/arch/riscv/include/asm/pgtable.h
@@ -72,6 +72,19 @@
 #define FIXADDR_SIZE     PGDIR_SIZE
 #endif
 #define FIXADDR_START    (FIXADDR_TOP - FIXADDR_SIZE)
+
+#ifdef CONFIG_XIP_KERNEL
+#define XIP_OFFSET		SZ_8M
+#define XIP_FIXUP(addr) ({							\
+	uintptr_t __a = (uintptr_t)(addr);					\
+	(__a >= CONFIG_XIP_PHYS_ADDR && __a < CONFIG_XIP_PHYS_ADDR + SZ_16M) ?	\
+		__a - CONFIG_XIP_PHYS_ADDR + CONFIG_PHYS_RAM_BASE - XIP_OFFSET :\
+		__a;								\
+	})
+#else
+#define XIP_FIXUP(addr)		(addr)
+#endif /* CONFIG_XIP_KERNEL */
+
 #endif
 
 #ifndef __ASSEMBLY__
@@ -507,8 +520,16 @@ static inline int ptep_clear_flush_young(struct vm_area_struct *vma,
 #define kern_addr_valid(addr)   (1) /* FIXME */
 
 extern char _start[];
-extern void *dtb_early_va;
-extern uintptr_t dtb_early_pa;
+extern void *_dtb_early_va;
+extern uintptr_t _dtb_early_pa;
+#if defined(CONFIG_XIP_KERNEL) && defined(CONFIG_MMU)
+#define dtb_early_va	(*(void **)XIP_FIXUP(&_dtb_early_va))
+#define dtb_early_pa	(*(uintptr_t *)XIP_FIXUP(&_dtb_early_pa))
+#else
+#define dtb_early_va	_dtb_early_va
+#define dtb_early_pa	_dtb_early_pa
+#endif /* CONFIG_XIP_KERNEL */
+
 void setup_bootmem(void);
 void paging_init(void);
 void misc_mem_init(void);