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linux/arch/arm64/kernel/head.S
Catalin Marinas 9703d9d7f7 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>
2012-09-17 10:24:45 +01:00

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/*
* 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)
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