avr32: Add simple paging support
Use the MMU hardware to set up 1:1 mappings between physical and virtual
addresses. This allows us to bypass the cache when accessing the flash
without having to do any physical-to-virtual address mapping in the CFI
driver.
The virtual memory mappings are defined at compile time through a sorted
array of virtual memory range objects. When a TLB miss exception
happens, the exception handler does a binary search through the array
until it finds a matching entry and loads it into the TLB. The u-boot
image itself is covered by a fixed TLB entry which is never replaced.
This makes the 'saveenv' command work again on ATNGW100 and other boards
using the CFI driver, hopefully without breaking any rules.
Signed-off-by: Haavard Skinnemoen <haavard.skinnemoen@atmel.com>
diff --git a/arch/avr32/cpu/at32ap700x/Makefile b/arch/avr32/cpu/at32ap700x/Makefile
index 46e6ef6..30ea925 100644
--- a/arch/avr32/cpu/at32ap700x/Makefile
+++ b/arch/avr32/cpu/at32ap700x/Makefile
@@ -24,7 +24,7 @@
LIB := $(obj)lib$(SOC).a
-COBJS := portmux.o clk.o
+COBJS := portmux.o clk.o mmu.o
SRCS := $(SOBJS:.o=.S) $(COBJS:.o=.c)
OBJS := $(addprefix $(obj),$(SOBJS) $(COBJS))
diff --git a/arch/avr32/cpu/at32ap700x/mmu.c b/arch/avr32/cpu/at32ap700x/mmu.c
new file mode 100644
index 0000000..c3a1b93
--- /dev/null
+++ b/arch/avr32/cpu/at32ap700x/mmu.c
@@ -0,0 +1,78 @@
+#include <common.h>
+#include <asm/arch/mmu.h>
+#include <asm/sysreg.h>
+
+void mmu_init_r(unsigned long dest_addr)
+{
+ uintptr_t vmr_table_addr;
+
+ /* Round monitor address down to the nearest page boundary */
+ dest_addr &= PAGE_ADDR_MASK;
+
+ /* Initialize TLB entry 0 to cover the monitor, and lock it */
+ sysreg_write(TLBEHI, dest_addr | SYSREG_BIT(TLBEHI_V));
+ sysreg_write(TLBELO, dest_addr | MMU_VMR_CACHE_WRBACK);
+ sysreg_write(MMUCR, SYSREG_BF(DRP, 0) | SYSREG_BF(DLA, 1)
+ | SYSREG_BIT(MMUCR_S) | SYSREG_BIT(M));
+ __builtin_tlbw();
+
+ /*
+ * Calculate the address of the VM range table in a PC-relative
+ * manner to make sure we hit the SDRAM and not the flash.
+ */
+ vmr_table_addr = (uintptr_t)&mmu_vmr_table;
+ sysreg_write(PTBR, vmr_table_addr);
+ printf("VMR table @ 0x%08x\n", vmr_table_addr);
+
+ /* Enable paging */
+ sysreg_write(MMUCR, SYSREG_BF(DRP, 1) | SYSREG_BF(DLA, 1)
+ | SYSREG_BIT(MMUCR_S) | SYSREG_BIT(M) | SYSREG_BIT(E));
+}
+
+int mmu_handle_tlb_miss(void)
+{
+ const struct mmu_vm_range *vmr_table;
+ const struct mmu_vm_range *vmr;
+ unsigned int fault_pgno;
+ int first, last;
+
+ fault_pgno = sysreg_read(TLBEAR) >> PAGE_SHIFT;
+ vmr_table = (const struct mmu_vm_range *)sysreg_read(PTBR);
+
+ /* Do a binary search through the VM ranges */
+ first = 0;
+ last = CONFIG_SYS_NR_VM_REGIONS;
+ while (first < last) {
+ unsigned int start;
+ int middle;
+
+ /* Pick the entry in the middle of the remaining range */
+ middle = (first + last) >> 1;
+ vmr = &vmr_table[middle];
+ start = vmr->virt_pgno;
+
+ /* Do the bisection thing */
+ if (fault_pgno < start) {
+ last = middle;
+ } else if (fault_pgno >= (start + vmr->nr_pages)) {
+ first = middle + 1;
+ } else {
+ /* Got it; let's slam it into the TLB */
+ uint32_t tlbelo;
+
+ tlbelo = vmr->phys & ~PAGE_ADDR_MASK;
+ tlbelo |= fault_pgno << PAGE_SHIFT;
+ sysreg_write(TLBELO, tlbelo);
+ __builtin_tlbw();
+
+ /* Zero means success */
+ return 0;
+ }
+ }
+
+ /*
+ * Didn't find any matching entries. Return a nonzero value to
+ * indicate that this should be treated as a fatal exception.
+ */
+ return -1;
+}
diff --git a/arch/avr32/cpu/start.S b/arch/avr32/cpu/start.S
index 99c9e06..06bf4c6 100644
--- a/arch/avr32/cpu/start.S
+++ b/arch/avr32/cpu/start.S
@@ -82,12 +82,19 @@
.org 0x44
rjmp unknown_exception /* DTLB Modified */
- .org 0x50
- rjmp unknown_exception /* ITLB Miss */
- .org 0x60
- rjmp unknown_exception /* DTLB Miss (read) */
- .org 0x70
- rjmp unknown_exception /* DTLB Miss (write) */
+ .org 0x50 /* ITLB Miss */
+ pushm r8-r12,lr
+ rjmp 1f
+ .org 0x60 /* DTLB Miss (read) */
+ pushm r8-r12,lr
+ rjmp 1f
+ .org 0x70 /* DTLB Miss (write) */
+ pushm r8-r12,lr
+1: mov r12, sp
+ rcall mmu_handle_tlb_miss
+ popm r8-r12,lr
+ brne unknown_exception
+ rete
.size _evba, . - _evba
diff --git a/arch/avr32/include/asm/arch-at32ap700x/addrspace.h b/arch/avr32/include/asm/arch-at32ap700x/addrspace.h
index 409eee3..4edc1bd 100644
--- a/arch/avr32/include/asm/arch-at32ap700x/addrspace.h
+++ b/arch/avr32/include/asm/arch-at32ap700x/addrspace.h
@@ -75,10 +75,7 @@
static inline void *
map_physmem(phys_addr_t paddr, unsigned long len, unsigned long flags)
{
- if (flags == MAP_WRBACK)
- return (void *)P1SEGADDR(paddr);
- else
- return (void *)P2SEGADDR(paddr);
+ return (void *)paddr;
}
#endif /* __ASM_AVR32_ADDRSPACE_H */
diff --git a/arch/avr32/include/asm/arch-at32ap700x/mmu.h b/arch/avr32/include/asm/arch-at32ap700x/mmu.h
new file mode 100644
index 0000000..fcd9a05
--- /dev/null
+++ b/arch/avr32/include/asm/arch-at32ap700x/mmu.h
@@ -0,0 +1,66 @@
+/*
+ * In order to deal with the hardcoded u-boot requirement that virtual
+ * addresses are always mapped 1:1 with physical addresses, we implement
+ * a small virtual memory manager so that we can use the MMU hardware in
+ * order to get the caching properties right.
+ *
+ * A few pages (or possibly just one) are locked in the TLB permanently
+ * in order to avoid recursive TLB misses, but most pages are faulted in
+ * on demand.
+ */
+#ifndef __ASM_ARCH_MMU_H
+#define __ASM_ARCH_MMU_H
+
+#include <asm/sysreg.h>
+
+#define PAGE_SHIFT 20
+#define PAGE_SIZE (1UL << PAGE_SHIFT)
+#define PAGE_ADDR_MASK (~(PAGE_SIZE - 1))
+
+#define MMU_VMR_CACHE_NONE \
+ (SYSREG_BF(AP, 3) | SYSREG_BF(SZ, 3) | SYSREG_BIT(TLBELO_D))
+#define MMU_VMR_CACHE_WBUF \
+ (MMU_VMR_CACHE_NONE | SYSREG_BIT(B))
+#define MMU_VMR_CACHE_WRTHRU \
+ (MMU_VMR_CACHE_NONE | SYSREG_BIT(TLBELO_C) | SYSREG_BIT(W))
+#define MMU_VMR_CACHE_WRBACK \
+ (MMU_VMR_CACHE_WBUF | SYSREG_BIT(TLBELO_C))
+
+/*
+ * This structure is used in our "page table". Instead of the usual
+ * x86-inspired radix tree, we let each entry cover an arbitrary-sized
+ * virtual address range and store them in a binary search tree. This is
+ * somewhat slower, but should use significantly less RAM, and we
+ * shouldn't get many TLB misses when using 1 MB pages anyway.
+ *
+ * With 1 MB pages, we need 12 bits to store the page number. In
+ * addition, we stick an Invalid bit in the high bit of virt_pgno (if
+ * set, it cannot possibly match any faulting page), and all the bits
+ * that need to be written to TLBELO in phys_pgno.
+ */
+struct mmu_vm_range {
+ uint16_t virt_pgno;
+ uint16_t nr_pages;
+ uint32_t phys;
+};
+
+/*
+ * An array of mmu_vm_range objects describing all pageable addresses.
+ * The array is sorted by virt_pgno so that the TLB miss exception
+ * handler can do a binary search to find the correct entry.
+ */
+extern struct mmu_vm_range mmu_vmr_table[];
+
+/*
+ * Initialize the MMU. This will set up a fixed TLB entry for the static
+ * u-boot image at dest_addr and enable paging.
+ */
+void mmu_init_r(unsigned long dest_addr);
+
+/*
+ * Handle a TLB miss exception. This function is called directly from
+ * the exception vector table written in assembly.
+ */
+int mmu_handle_tlb_miss(void);
+
+#endif /* __ASM_ARCH_MMU_H */
diff --git a/arch/avr32/lib/board.c b/arch/avr32/lib/board.c
index 9e741d2..aa589bb 100644
--- a/arch/avr32/lib/board.c
+++ b/arch/avr32/lib/board.c
@@ -33,6 +33,7 @@
#include <asm/initcalls.h>
#include <asm/sections.h>
+#include <asm/arch/mmu.h>
#ifndef CONFIG_IDENT_STRING
#define CONFIG_IDENT_STRING ""
@@ -265,6 +266,9 @@
gd->flags |= GD_FLG_RELOC;
gd->reloc_off = dest_addr - CONFIG_SYS_MONITOR_BASE;
+ /* Enable the MMU so that we can keep u-boot simple */
+ mmu_init_r(dest_addr);
+
board_early_init_r();
monitor_flash_len = _edata - _text;