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/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;
+}