arm64: Kernel booting and initialisation
The patch adds the kernel booting and the initial setup code.
Documentation/arm64/booting.txt describes the booting protocol on the
AArch64 Linux kernel. This is subject to change following the work on
boot standardisation, ACPI.
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Acked-by: Nicolas Pitre <nico@linaro.org>
Acked-by: Tony Lindgren <tony@atomide.com>
Acked-by: Olof Johansson <olof@lixom.net>
Acked-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
new file mode 100644
index 0000000..a2f02b6
--- /dev/null
+++ b/arch/arm64/kernel/head.S
@@ -0,0 +1,510 @@
+/*
+ * Low-level CPU initialisation
+ * Based on arch/arm/kernel/head.S
+ *
+ * Copyright (C) 1994-2002 Russell King
+ * Copyright (C) 2003-2012 ARM Ltd.
+ * Authors: Catalin Marinas <catalin.marinas@arm.com>
+ * Will Deacon <will.deacon@arm.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <linux/linkage.h>
+#include <linux/init.h>
+
+#include <asm/assembler.h>
+#include <asm/ptrace.h>
+#include <asm/asm-offsets.h>
+#include <asm/memory.h>
+#include <asm/thread_info.h>
+#include <asm/pgtable-hwdef.h>
+#include <asm/pgtable.h>
+#include <asm/page.h>
+
+/*
+ * swapper_pg_dir is the virtual address of the initial page table. We place
+ * the page tables 3 * PAGE_SIZE below KERNEL_RAM_VADDR. The idmap_pg_dir has
+ * 2 pages and is placed below swapper_pg_dir.
+ */
+#define KERNEL_RAM_VADDR (PAGE_OFFSET + TEXT_OFFSET)
+
+#if (KERNEL_RAM_VADDR & 0xfffff) != 0x80000
+#error KERNEL_RAM_VADDR must start at 0xXXX80000
+#endif
+
+#define SWAPPER_DIR_SIZE (3 * PAGE_SIZE)
+#define IDMAP_DIR_SIZE (2 * PAGE_SIZE)
+
+ .globl swapper_pg_dir
+ .equ swapper_pg_dir, KERNEL_RAM_VADDR - SWAPPER_DIR_SIZE
+
+ .globl idmap_pg_dir
+ .equ idmap_pg_dir, swapper_pg_dir - IDMAP_DIR_SIZE
+
+ .macro pgtbl, ttb0, ttb1, phys
+ add \ttb1, \phys, #TEXT_OFFSET - SWAPPER_DIR_SIZE
+ sub \ttb0, \ttb1, #IDMAP_DIR_SIZE
+ .endm
+
+#ifdef CONFIG_ARM64_64K_PAGES
+#define BLOCK_SHIFT PAGE_SHIFT
+#define BLOCK_SIZE PAGE_SIZE
+#else
+#define BLOCK_SHIFT SECTION_SHIFT
+#define BLOCK_SIZE SECTION_SIZE
+#endif
+
+#define KERNEL_START KERNEL_RAM_VADDR
+#define KERNEL_END _end
+
+/*
+ * Initial memory map attributes.
+ */
+#ifndef CONFIG_SMP
+#define PTE_FLAGS PTE_TYPE_PAGE | PTE_AF
+#define PMD_FLAGS PMD_TYPE_SECT | PMD_SECT_AF
+#else
+#define PTE_FLAGS PTE_TYPE_PAGE | PTE_AF | PTE_SHARED
+#define PMD_FLAGS PMD_TYPE_SECT | PMD_SECT_AF | PMD_SECT_S
+#endif
+
+#ifdef CONFIG_ARM64_64K_PAGES
+#define MM_MMUFLAGS PTE_ATTRINDX(MT_NORMAL) | PTE_FLAGS
+#define IO_MMUFLAGS PTE_ATTRINDX(MT_DEVICE_nGnRE) | PTE_XN | PTE_FLAGS
+#else
+#define MM_MMUFLAGS PMD_ATTRINDX(MT_NORMAL) | PMD_FLAGS
+#define IO_MMUFLAGS PMD_ATTRINDX(MT_DEVICE_nGnRE) | PMD_SECT_XN | PMD_FLAGS
+#endif
+
+/*
+ * Kernel startup entry point.
+ * ---------------------------
+ *
+ * The requirements are:
+ * MMU = off, D-cache = off, I-cache = on or off,
+ * x0 = physical address to the FDT blob.
+ *
+ * This code is mostly position independent so you call this at
+ * __pa(PAGE_OFFSET + TEXT_OFFSET).
+ *
+ * Note that the callee-saved registers are used for storing variables
+ * that are useful before the MMU is enabled. The allocations are described
+ * in the entry routines.
+ */
+ __HEAD
+
+ /*
+ * DO NOT MODIFY. Image header expected by Linux boot-loaders.
+ */
+ b stext // branch to kernel start, magic
+ .long 0 // reserved
+ .quad TEXT_OFFSET // Image load offset from start of RAM
+ .quad 0 // reserved
+ .quad 0 // reserved
+
+ENTRY(stext)
+ mov x21, x0 // x21=FDT
+ bl el2_setup // Drop to EL1
+ mrs x22, midr_el1 // x22=cpuid
+ mov x0, x22
+ bl lookup_processor_type
+ mov x23, x0 // x23=current cpu_table
+ cbz x23, __error_p // invalid processor (x23=0)?
+ bl __calc_phys_offset // x24=PHYS_OFFSET, x28=PHYS_OFFSET-PAGE_OFFSET
+ bl __vet_fdt
+ bl __create_page_tables // x25=TTBR0, x26=TTBR1
+ /*
+ * The following calls CPU specific code in a position independent
+ * manner. See arch/arm64/mm/proc.S for details. x23 = base of
+ * cpu_info structure selected by lookup_processor_type above.
+ * On return, the CPU will be ready for the MMU to be turned on and
+ * the TCR will have been set.
+ */
+ ldr x27, __switch_data // address to jump to after
+ // MMU has been enabled
+ adr lr, __enable_mmu // return (PIC) address
+ ldr x12, [x23, #CPU_INFO_SETUP]
+ add x12, x12, x28 // __virt_to_phys
+ br x12 // initialise processor
+ENDPROC(stext)
+
+/*
+ * If we're fortunate enough to boot at EL2, ensure that the world is
+ * sane before dropping to EL1.
+ */
+ENTRY(el2_setup)
+ mrs x0, CurrentEL
+ cmp x0, #PSR_MODE_EL2t
+ ccmp x0, #PSR_MODE_EL2h, #0x4, ne
+ b.eq 1f
+ ret
+
+ /* Hyp configuration. */
+1: mov x0, #(1 << 31) // 64-bit EL1
+ msr hcr_el2, x0
+
+ /* Generic timers. */
+ mrs x0, cnthctl_el2
+ orr x0, x0, #3 // Enable EL1 physical timers
+ msr cnthctl_el2, x0
+
+ /* Populate ID registers. */
+ mrs x0, midr_el1
+ mrs x1, mpidr_el1
+ msr vpidr_el2, x0
+ msr vmpidr_el2, x1
+
+ /* sctlr_el1 */
+ mov x0, #0x0800 // Set/clear RES{1,0} bits
+ movk x0, #0x30d0, lsl #16
+ msr sctlr_el1, x0
+
+ /* Coprocessor traps. */
+ mov x0, #0x33ff
+ msr cptr_el2, x0 // Disable copro. traps to EL2
+
+#ifdef CONFIG_COMPAT
+ msr hstr_el2, xzr // Disable CP15 traps to EL2
+#endif
+
+ /* spsr */
+ mov x0, #(PSR_F_BIT | PSR_I_BIT | PSR_A_BIT | PSR_D_BIT |\
+ PSR_MODE_EL1h)
+ msr spsr_el2, x0
+ msr elr_el2, lr
+ eret
+ENDPROC(el2_setup)
+
+ .align 3
+2: .quad .
+ .quad PAGE_OFFSET
+
+#ifdef CONFIG_SMP
+ .pushsection .smp.pen.text, "ax"
+ .align 3
+1: .quad .
+ .quad secondary_holding_pen_release
+
+ /*
+ * This provides a "holding pen" for platforms to hold all secondary
+ * cores are held until we're ready for them to initialise.
+ */
+ENTRY(secondary_holding_pen)
+ bl el2_setup // Drop to EL1
+ mrs x0, mpidr_el1
+ and x0, x0, #15 // CPU number
+ adr x1, 1b
+ ldp x2, x3, [x1]
+ sub x1, x1, x2
+ add x3, x3, x1
+pen: ldr x4, [x3]
+ cmp x4, x0
+ b.eq secondary_startup
+ wfe
+ b pen
+ENDPROC(secondary_holding_pen)
+ .popsection
+
+ENTRY(secondary_startup)
+ /*
+ * Common entry point for secondary CPUs.
+ */
+ mrs x22, midr_el1 // x22=cpuid
+ mov x0, x22
+ bl lookup_processor_type
+ mov x23, x0 // x23=current cpu_table
+ cbz x23, __error_p // invalid processor (x23=0)?
+
+ bl __calc_phys_offset // x24=phys offset
+ pgtbl x25, x26, x24 // x25=TTBR0, x26=TTBR1
+ ldr x12, [x23, #CPU_INFO_SETUP]
+ add x12, x12, x28 // __virt_to_phys
+ blr x12 // initialise processor
+
+ ldr x21, =secondary_data
+ ldr x27, =__secondary_switched // address to jump to after enabling the MMU
+ b __enable_mmu
+ENDPROC(secondary_startup)
+
+ENTRY(__secondary_switched)
+ ldr x0, [x21] // get secondary_data.stack
+ mov sp, x0
+ mov x29, #0
+ b secondary_start_kernel
+ENDPROC(__secondary_switched)
+#endif /* CONFIG_SMP */
+
+/*
+ * Setup common bits before finally enabling the MMU. Essentially this is just
+ * loading the page table pointer and vector base registers.
+ *
+ * On entry to this code, x0 must contain the SCTLR_EL1 value for turning on
+ * the MMU.
+ */
+__enable_mmu:
+ ldr x5, =vectors
+ msr vbar_el1, x5
+ msr ttbr0_el1, x25 // load TTBR0
+ msr ttbr1_el1, x26 // load TTBR1
+ isb
+ b __turn_mmu_on
+ENDPROC(__enable_mmu)
+
+/*
+ * Enable the MMU. This completely changes the structure of the visible memory
+ * space. You will not be able to trace execution through this.
+ *
+ * x0 = system control register
+ * x27 = *virtual* address to jump to upon completion
+ *
+ * other registers depend on the function called upon completion
+ */
+ .align 6
+__turn_mmu_on:
+ msr sctlr_el1, x0
+ isb
+ br x27
+ENDPROC(__turn_mmu_on)
+
+/*
+ * Calculate the start of physical memory.
+ */
+__calc_phys_offset:
+ adr x0, 1f
+ ldp x1, x2, [x0]
+ sub x28, x0, x1 // x28 = PHYS_OFFSET - PAGE_OFFSET
+ add x24, x2, x28 // x24 = PHYS_OFFSET
+ ret
+ENDPROC(__calc_phys_offset)
+
+ .align 3
+1: .quad .
+ .quad PAGE_OFFSET
+
+/*
+ * Macro to populate the PGD for the corresponding block entry in the next
+ * level (tbl) for the given virtual address.
+ *
+ * Preserves: pgd, tbl, virt
+ * Corrupts: tmp1, tmp2
+ */
+ .macro create_pgd_entry, pgd, tbl, virt, tmp1, tmp2
+ lsr \tmp1, \virt, #PGDIR_SHIFT
+ and \tmp1, \tmp1, #PTRS_PER_PGD - 1 // PGD index
+ orr \tmp2, \tbl, #3 // PGD entry table type
+ str \tmp2, [\pgd, \tmp1, lsl #3]
+ .endm
+
+/*
+ * Macro to populate block entries in the page table for the start..end
+ * virtual range (inclusive).
+ *
+ * Preserves: tbl, flags
+ * Corrupts: phys, start, end, pstate
+ */
+ .macro create_block_map, tbl, flags, phys, start, end, idmap=0
+ lsr \phys, \phys, #BLOCK_SHIFT
+ .if \idmap
+ and \start, \phys, #PTRS_PER_PTE - 1 // table index
+ .else
+ lsr \start, \start, #BLOCK_SHIFT
+ and \start, \start, #PTRS_PER_PTE - 1 // table index
+ .endif
+ orr \phys, \flags, \phys, lsl #BLOCK_SHIFT // table entry
+ .ifnc \start,\end
+ lsr \end, \end, #BLOCK_SHIFT
+ and \end, \end, #PTRS_PER_PTE - 1 // table end index
+ .endif
+9999: str \phys, [\tbl, \start, lsl #3] // store the entry
+ .ifnc \start,\end
+ add \start, \start, #1 // next entry
+ add \phys, \phys, #BLOCK_SIZE // next block
+ cmp \start, \end
+ b.ls 9999b
+ .endif
+ .endm
+
+/*
+ * Setup the initial page tables. We only setup the barest amount which is
+ * required to get the kernel running. The following sections are required:
+ * - identity mapping to enable the MMU (low address, TTBR0)
+ * - first few MB of the kernel linear mapping to jump to once the MMU has
+ * been enabled, including the FDT blob (TTBR1)
+ */
+__create_page_tables:
+ pgtbl x25, x26, x24 // idmap_pg_dir and swapper_pg_dir addresses
+
+ /*
+ * Clear the idmap and swapper page tables.
+ */
+ mov x0, x25
+ add x6, x26, #SWAPPER_DIR_SIZE
+1: stp xzr, xzr, [x0], #16
+ stp xzr, xzr, [x0], #16
+ stp xzr, xzr, [x0], #16
+ stp xzr, xzr, [x0], #16
+ cmp x0, x6
+ b.lo 1b
+
+ ldr x7, =MM_MMUFLAGS
+
+ /*
+ * Create the identity mapping.
+ */
+ add x0, x25, #PAGE_SIZE // section table address
+ adr x3, __turn_mmu_on // virtual/physical address
+ create_pgd_entry x25, x0, x3, x5, x6
+ create_block_map x0, x7, x3, x5, x5, idmap=1
+
+ /*
+ * Map the kernel image (starting with PHYS_OFFSET).
+ */
+ add x0, x26, #PAGE_SIZE // section table address
+ mov x5, #PAGE_OFFSET
+ create_pgd_entry x26, x0, x5, x3, x6
+ ldr x6, =KERNEL_END - 1
+ mov x3, x24 // phys offset
+ create_block_map x0, x7, x3, x5, x6
+
+ /*
+ * Map the FDT blob (maximum 2MB; must be within 512MB of
+ * PHYS_OFFSET).
+ */
+ mov x3, x21 // FDT phys address
+ and x3, x3, #~((1 << 21) - 1) // 2MB aligned
+ mov x6, #PAGE_OFFSET
+ sub x5, x3, x24 // subtract PHYS_OFFSET
+ tst x5, #~((1 << 29) - 1) // within 512MB?
+ csel x21, xzr, x21, ne // zero the FDT pointer
+ b.ne 1f
+ add x5, x5, x6 // __va(FDT blob)
+ add x6, x5, #1 << 21 // 2MB for the FDT blob
+ sub x6, x6, #1 // inclusive range
+ create_block_map x0, x7, x3, x5, x6
+1:
+ ret
+ENDPROC(__create_page_tables)
+ .ltorg
+
+ .align 3
+ .type __switch_data, %object
+__switch_data:
+ .quad __mmap_switched
+ .quad __data_loc // x4
+ .quad _data // x5
+ .quad __bss_start // x6
+ .quad _end // x7
+ .quad processor_id // x4
+ .quad __fdt_pointer // x5
+ .quad memstart_addr // x6
+ .quad init_thread_union + THREAD_START_SP // sp
+
+/*
+ * The following fragment of code is executed with the MMU on in MMU mode, and
+ * uses absolute addresses; this is not position independent.
+ */
+__mmap_switched:
+ adr x3, __switch_data + 8
+
+ ldp x4, x5, [x3], #16
+ ldp x6, x7, [x3], #16
+ cmp x4, x5 // Copy data segment if needed
+1: ccmp x5, x6, #4, ne
+ b.eq 2f
+ ldr x16, [x4], #8
+ str x16, [x5], #8
+ b 1b
+2:
+1: cmp x6, x7
+ b.hs 2f
+ str xzr, [x6], #8 // Clear BSS
+ b 1b
+2:
+ ldp x4, x5, [x3], #16
+ ldr x6, [x3], #8
+ ldr x16, [x3]
+ mov sp, x16
+ str x22, [x4] // Save processor ID
+ str x21, [x5] // Save FDT pointer
+ str x24, [x6] // Save PHYS_OFFSET
+ mov x29, #0
+ b start_kernel
+ENDPROC(__mmap_switched)
+
+/*
+ * Exception handling. Something went wrong and we can't proceed. We ought to
+ * tell the user, but since we don't have any guarantee that we're even
+ * running on the right architecture, we do virtually nothing.
+ */
+__error_p:
+ENDPROC(__error_p)
+
+__error:
+1: nop
+ b 1b
+ENDPROC(__error)
+
+/*
+ * This function gets the processor ID in w0 and searches the cpu_table[] for
+ * a match. It returns a pointer to the struct cpu_info it found. The
+ * cpu_table[] must end with an empty (all zeros) structure.
+ *
+ * This routine can be called via C code and it needs to work with the MMU
+ * both disabled and enabled (the offset is calculated automatically).
+ */
+ENTRY(lookup_processor_type)
+ adr x1, __lookup_processor_type_data
+ ldp x2, x3, [x1]
+ sub x1, x1, x2 // get offset between VA and PA
+ add x3, x3, x1 // convert VA to PA
+1:
+ ldp w5, w6, [x3] // load cpu_id_val and cpu_id_mask
+ cbz w5, 2f // end of list?
+ and w6, w6, w0
+ cmp w5, w6
+ b.eq 3f
+ add x3, x3, #CPU_INFO_SZ
+ b 1b
+2:
+ mov x3, #0 // unknown processor
+3:
+ mov x0, x3
+ ret
+ENDPROC(lookup_processor_type)
+
+ .align 3
+ .type __lookup_processor_type_data, %object
+__lookup_processor_type_data:
+ .quad .
+ .quad cpu_table
+ .size __lookup_processor_type_data, . - __lookup_processor_type_data
+
+/*
+ * Determine validity of the x21 FDT pointer.
+ * The dtb must be 8-byte aligned and live in the first 512M of memory.
+ */
+__vet_fdt:
+ tst x21, #0x7
+ b.ne 1f
+ cmp x21, x24
+ b.lt 1f
+ mov x0, #(1 << 29)
+ add x0, x0, x24
+ cmp x21, x0
+ b.ge 1f
+ ret
+1:
+ mov x21, #0
+ ret
+ENDPROC(__vet_fdt)