irqchip: gic-v3: Initial support for GICv3

[mirror_ubuntu-zesty-kernel.git] / arch / arm64 / kernel / head.S

/*
 * 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 <linux/irqchip/arm-gic-v3.h>

#include <asm/assembler.h>
#include <asm/ptrace.h>
#include <asm/asm-offsets.h>
#include <asm/cache.h>
#include <asm/cputype.h>
#include <asm/memory.h>
#include <asm/thread_info.h>
#include <asm/pgtable-hwdef.h>
#include <asm/pgtable.h>
#include <asm/page.h>
#include <asm/virt.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
#else
#define MM_MMUFLAGS     PMD_ATTRINDX(MT_NORMAL) | 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.
         */
#ifdef CONFIG_EFI
efi_head:
        /*
         * This add instruction has no meaningful effect except that
         * its opcode forms the magic "MZ" signature required by UEFI.
         */
        add     x13, x18, #0x16
        b       stext
#else
        b       stext                           // branch to kernel start, magic
        .long   0                               // reserved
#endif
        .quad   TEXT_OFFSET                     // Image load offset from start of RAM
        .quad   0                               // reserved
        .quad   0                               // reserved
        .quad   0                               // reserved
        .quad   0                               // reserved
        .quad   0                               // reserved
        .byte   0x41                            // Magic number, "ARM\x64"
        .byte   0x52
        .byte   0x4d
        .byte   0x64
#ifdef CONFIG_EFI
        .long   pe_header - efi_head            // Offset to the PE header.
#else
        .word   0                               // reserved
#endif

#ifdef CONFIG_EFI
        .align 3
pe_header:
        .ascii  "PE"
        .short  0
coff_header:
        .short  0xaa64                          // AArch64
        .short  2                               // nr_sections
        .long   0                               // TimeDateStamp
        .long   0                               // PointerToSymbolTable
        .long   1                               // NumberOfSymbols
        .short  section_table - optional_header // SizeOfOptionalHeader
        .short  0x206                           // Characteristics.
                                                // IMAGE_FILE_DEBUG_STRIPPED |
                                                // IMAGE_FILE_EXECUTABLE_IMAGE |
                                                // IMAGE_FILE_LINE_NUMS_STRIPPED
optional_header:
        .short  0x20b                           // PE32+ format
        .byte   0x02                            // MajorLinkerVersion
        .byte   0x14                            // MinorLinkerVersion
        .long   _edata - stext                  // SizeOfCode
        .long   0                               // SizeOfInitializedData
        .long   0                               // SizeOfUninitializedData
        .long   efi_stub_entry - efi_head       // AddressOfEntryPoint
        .long   stext - efi_head                // BaseOfCode

extra_header_fields:
        .quad   0                               // ImageBase
        .long   0x20                            // SectionAlignment
        .long   0x8                             // FileAlignment
        .short  0                               // MajorOperatingSystemVersion
        .short  0                               // MinorOperatingSystemVersion
        .short  0                               // MajorImageVersion
        .short  0                               // MinorImageVersion
        .short  0                               // MajorSubsystemVersion
        .short  0                               // MinorSubsystemVersion
        .long   0                               // Win32VersionValue

        .long   _edata - efi_head               // SizeOfImage

        // Everything before the kernel image is considered part of the header
        .long   stext - efi_head                // SizeOfHeaders
        .long   0                               // CheckSum
        .short  0xa                             // Subsystem (EFI application)
        .short  0                               // DllCharacteristics
        .quad   0                               // SizeOfStackReserve
        .quad   0                               // SizeOfStackCommit
        .quad   0                               // SizeOfHeapReserve
        .quad   0                               // SizeOfHeapCommit
        .long   0                               // LoaderFlags
        .long   0x6                             // NumberOfRvaAndSizes

        .quad   0                               // ExportTable
        .quad   0                               // ImportTable
        .quad   0                               // ResourceTable
        .quad   0                               // ExceptionTable
        .quad   0                               // CertificationTable
        .quad   0                               // BaseRelocationTable

        // Section table
section_table:

        /*
         * The EFI application loader requires a relocation section
         * because EFI applications must be relocatable.  This is a
         * dummy section as far as we are concerned.
         */
        .ascii  ".reloc"
        .byte   0
        .byte   0                       // end of 0 padding of section name
        .long   0
        .long   0
        .long   0                       // SizeOfRawData
        .long   0                       // PointerToRawData
        .long   0                       // PointerToRelocations
        .long   0                       // PointerToLineNumbers
        .short  0                       // NumberOfRelocations
        .short  0                       // NumberOfLineNumbers
        .long   0x42100040              // Characteristics (section flags)


        .ascii  ".text"
        .byte   0
        .byte   0
        .byte   0                       // end of 0 padding of section name
        .long   _edata - stext          // VirtualSize
        .long   stext - efi_head        // VirtualAddress
        .long   _edata - stext          // SizeOfRawData
        .long   stext - efi_head        // PointerToRawData

        .long   0               // PointerToRelocations (0 for executables)
        .long   0               // PointerToLineNumbers (0 for executables)
        .short  0               // NumberOfRelocations  (0 for executables)
        .short  0               // NumberOfLineNumbers  (0 for executables)
        .long   0xe0500020      // Characteristics (section flags)
        .align 5
#endif

ENTRY(stext)
        mov     x21, x0                         // x21=FDT
        bl      el2_setup                       // Drop to EL1, w20=cpu_boot_mode
        bl      __calc_phys_offset              // x24=PHYS_OFFSET, x28=PHYS_OFFSET-PAGE_OFFSET
        bl      set_cpu_boot_mode_flag
        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      __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.
 *
 * Returns either BOOT_CPU_MODE_EL1 or BOOT_CPU_MODE_EL2 in x20 if
 * booted in EL1 or EL2 respectively.
 */
ENTRY(el2_setup)
        mrs     x0, CurrentEL
        cmp     x0, #PSR_MODE_EL2t
        ccmp    x0, #PSR_MODE_EL2h, #0x4, ne
        b.ne    1f
        mrs     x0, sctlr_el2
CPU_BE( orr     x0, x0, #(1 << 25)      )       // Set the EE bit for EL2
CPU_LE( bic     x0, x0, #(1 << 25)      )       // Clear the EE bit for EL2
        msr     sctlr_el2, x0
        b       2f
1:      mrs     x0, sctlr_el1
CPU_BE( orr     x0, x0, #(3 << 24)      )       // Set the EE and E0E bits for EL1
CPU_LE( bic     x0, x0, #(3 << 24)      )       // Clear the EE and E0E bits for EL1
        msr     sctlr_el1, x0
        mov     w20, #BOOT_CPU_MODE_EL1         // This cpu booted in EL1
        isb
        ret

        /* Hyp configuration. */
2:      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
        msr     cntvoff_el2, xzr                // Clear virtual offset

#ifdef CONFIG_ARM_GIC_V3
        /* GICv3 system register access */
        mrs     x0, id_aa64pfr0_el1
        ubfx    x0, x0, #24, #4
        cmp     x0, #1
        b.ne    3f

        mrs     x0, ICC_SRE_EL2
        orr     x0, x0, #ICC_SRE_EL2_SRE        // Set ICC_SRE_EL2.SRE==1
        orr     x0, x0, #ICC_SRE_EL2_ENABLE     // Set ICC_SRE_EL2.Enable==1
        msr     ICC_SRE_EL2, x0
        isb                                     // Make sure SRE is now set
        msr     ICH_HCR_EL2, xzr                // Reset ICC_HCR_EL2 to defaults

3:
#endif

        /* 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
CPU_BE( movk    x0, #0x33d0, lsl #16    )       // Set EE and E0E on BE systems
CPU_LE( movk    x0, #0x30d0, lsl #16    )       // Clear EE and E0E on LE systems
        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

        /* Stage-2 translation */
        msr     vttbr_el2, xzr

        /* Hypervisor stub */
        adr     x0, __hyp_stub_vectors
        msr     vbar_el2, x0

        /* 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
        mov     w20, #BOOT_CPU_MODE_EL2         // This CPU booted in EL2
        eret
ENDPROC(el2_setup)

/*
 * Sets the __boot_cpu_mode flag depending on the CPU boot mode passed
 * in x20. See arch/arm64/include/asm/virt.h for more info.
 */
ENTRY(set_cpu_boot_mode_flag)
        ldr     x1, =__boot_cpu_mode            // Compute __boot_cpu_mode
        add     x1, x1, x28
        cmp     w20, #BOOT_CPU_MODE_EL2
        b.ne    1f
        add     x1, x1, #4
1:      str     w20, [x1]                       // This CPU has booted in EL1
        dmb     sy
        dc      ivac, x1                        // Invalidate potentially stale cache line
        ret
ENDPROC(set_cpu_boot_mode_flag)

/*
 * We need to find out the CPU boot mode long after boot, so we need to
 * store it in a writable variable.
 *
 * This is not in .bss, because we set it sufficiently early that the boot-time
 * zeroing of .bss would clobber it.
 */
        .pushsection    .data..cacheline_aligned
ENTRY(__boot_cpu_mode)
        .align  L1_CACHE_SHIFT
        .long   BOOT_CPU_MODE_EL2
        .long   0
        .popsection

        .align  3
2:      .quad   .
        .quad   PAGE_OFFSET

#ifdef CONFIG_SMP
        .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, w20=cpu_boot_mode
        bl      __calc_phys_offset              // x24=PHYS_OFFSET, x28=PHYS_OFFSET-PAGE_OFFSET
        bl      set_cpu_boot_mode_flag
        mrs     x0, mpidr_el1
        ldr     x1, =MPIDR_HWID_BITMASK
        and     x0, x0, x1
        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)

        /*
         * Secondary entry point that jumps straight into the kernel. Only to
         * be used where CPUs are brought online dynamically by the kernel.
         */
ENTRY(secondary_entry)
        bl      el2_setup                       // Drop to EL1
        bl      __calc_phys_offset              // x24=PHYS_OFFSET, x28=PHYS_OFFSET-PAGE_OFFSET
        bl      set_cpu_boot_mode_flag
        b       secondary_startup
ENDPROC(secondary_entry)

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)?

        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
        lsr     \phys, \phys, #BLOCK_SHIFT
        lsr     \start, \start, #BLOCK_SHIFT
        and     \start, \start, #PTRS_PER_PTE - 1       // table index
        orr     \phys, \flags, \phys, lsl #BLOCK_SHIFT  // table entry
        lsr     \end, \end, #BLOCK_SHIFT
        and     \end, \end, #PTRS_PER_PTE - 1           // table end index
9999:   str     \phys, [\tbl, \start, lsl #3]           // store the entry
        add     \start, \start, #1                      // next entry
        add     \phys, \phys, #BLOCK_SIZE               // next block
        cmp     \start, \end
        b.ls    9999b
        .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)
 *   - pgd entry for fixed mappings (TTBR1)
 */
__create_page_tables:
        pgtbl   x25, x26, x24                   // idmap_pg_dir and swapper_pg_dir addresses
        mov     x27, lr

        /*
         * Invalidate the idmap and swapper page tables to avoid potential
         * dirty cache lines being evicted.
         */
        mov     x0, x25
        add     x1, x26, #SWAPPER_DIR_SIZE
        bl      __inval_cache_range

        /*
         * 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
        ldr     x3, =KERNEL_START
        add     x3, x3, x28                     // __pa(KERNEL_START)
        create_pgd_entry x25, x0, x3, x5, x6
        ldr     x6, =KERNEL_END
        mov     x5, x3                          // __pa(KERNEL_START)
        add     x6, x6, x28                     // __pa(KERNEL_END)
        create_block_map x0, x7, x3, x5, x6

        /*
         * 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
        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:
        /*
         * Create the pgd entry for the fixed mappings.
         */
        ldr     x5, =FIXADDR_TOP                // Fixed mapping virtual address
        add     x0, x26, #2 * PAGE_SIZE         // section table address
        create_pgd_entry x26, x0, x5, x6, x7

        /*
         * Since the page tables have been populated with non-cacheable
         * accesses (MMU disabled), invalidate the idmap and swapper page
         * tables again to remove any speculatively loaded cache lines.
         */
        mov     x0, x25
        add     x1, x26, #SWAPPER_DIR_SIZE
        bl      __inval_cache_range

        mov     lr, x27
        ret
ENDPROC(__create_page_tables)
        .ltorg

        .align  3
        .type   __switch_data, %object
__switch_data:
        .quad   __mmap_switched
        .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     x6, x7, [x3], #16
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)