The U-boot boot process, using Xilinx ZCU102 (Rev 1.0) as an example.

/*************************************************************************
 *
 * Startup Code (reset vector)
 *
 *************************************************************************/
...
master_cpu:
        bl    _main

 * This file handles the target-independent stages of the U-Boot
 * start-up where a C runtime environment is needed. Its entry point
 * is _main and is branched into from the target's start.S file.
 *
 * _main execution sequence is:
 *
 * 1. Set up initial environment for calling board_init_f().
 *    This environment only provides a stack and a place to store
 *    the GD ('global data') structure, both located in some readily
 *    available RAM (SRAM, locked cache...). In this context, VARIABLE
 *    global data, initialized or not (BSS), are UNAVAILABLE; only
 *    CONSTANT initialized data are available. GD should be zeroed
 *    before board_init_f() is called.

ENTRY(_main)

/*
 * Set up initial C runtime environment and call board_init_f(0).
 */
#if defined(CONFIG_TPL_BUILD) && defined(CONFIG_TPL_NEEDS_SEPARATE_STACK)
        ldr     x0, =(CONFIG_TPL_STACK)
#elif defined(CONFIG_SPL_BUILD) && defined(CONFIG_SPL_STACK)
        ldr     x0, =(CONFIG_SPL_STACK)
#elif defined(CONFIG_INIT_SP_RELATIVE)
        adr     x0, __bss_start
        add     x0, x0, #CONFIG_SYS_INIT_SP_BSS_OFFSET
#else
        ldr     x0, =(CONFIG_SYS_INIT_SP_ADDR)
#endif
        bic     sp, x0, #0xf    /* 16-byte alignment for ABI compliance */
        mov     x0, sp
        bl      board_init_f_alloc_reserve
        mov     sp, x0
        /* set up gd here, outside any C code */
        mov     x18, x0
        bl      board_init_f_init_reserve

 * 2. Call board_init_f(). This function prepares the hardware for
 *    execution from system RAM (DRAM, DDR...) As system RAM may not
 *    be available yet, , board_init_f() must use the current GD to
 *    store any data which must be passed on to later stages. These
 *    data include the relocation destination, the future stack, and
 *    the future GD location.

        mov     x0, #0
        bl      board_init_f

 * 3. Set up intermediate environment where the stack and GD are the
 *    ones allocated by board_init_f() in system RAM, but BSS and
 *    initialized non-const data are still not available.

 * 4a.For U-Boot proper (not SPL), call relocate_code(). This function
 *    relocates U-Boot from its current location into the relocation
 *    destination computed by board_init_f().

 * 4b.For SPL, board_init_f() just returns (to crt0). There is no
 *    code relocation in SPL.

 * 5. Set up final environment for calling board_init_r(). This
 *    environment has BSS (initialized to 0), initialized non-const
 *    data (initialized to their intended value), and stack in system
 *    RAM (for SPL moving the stack and GD into RAM is optional - see
 *    CONFIG_SPL_STACK_R). GD has retained values set by board_init_f().

 * 6. For U-Boot proper (not SPL), some CPUs have some work left to do
 *    at this point regarding memory, so call c_runtime_cpu_setup.

 * 7. Branch to board_init_r().

• arch/arm/mach-zynq/cpu.c
• arch/arm/mach-zynq/spl.c

#if defined(CONFIG_ARCH_EARLY_INIT_R)
int arch_early_init_r(void)
{
#if (defined(CONFIG_FPGA) && !defined(CONFIG_SPL_BUILD)) || \
    (defined(CONFIG_SPL_FPGA_SUPPORT) && defined(CONFIG_SPL_BUILD))
        int cpu_id = cpu_desc_id();

        if (cpu_id < 0)
                return 0;

        fpga.size = zynq_fpga_descs[cpu_id].fpga_size;
        fpga.name = zynq_fpga_descs[cpu_id].devicename;
        fpga_init();
        fpga_add(fpga_xilinx, &fpga);
#endif
        return 0;
}
#endif

#ifdef CONFIG_MMC
static int initr_mmc(void)
{
        puts("MMC:   ");
        mmc_initialize(gd->bd);
        return 0;
}
#endif

static int initr_env(void)
{
        /* initialize environment */
        if (should_load_env())
                env_relocate();
        else
                set_default_env(NULL, 0);
#ifdef CONFIG_OF_CONTROL
        env_set_hex("fdtcontroladdr",
                    (unsigned long)map_to_sysmem(gd->fdt_blob));
#endif

        /* Initialize from environment */
        load_addr = env_get_ulong("loadaddr", 16, load_addr);

        return 0;
}

From common/board_info.c:

int __weak checkboard(void)
{
        return 0;
}

/*
 * If the root node of the DTB has a "model" property, show it.
 * Then call checkboard().
 */
int __weak show_board_info(void)
{
#ifdef CONFIG_OF_CONTROL
        DECLARE_GLOBAL_DATA_PTR;
        const char *model;

        model = fdt_getprop(gd->fdt_blob, 0, "model", NULL);

        if (model)
                printf("Model: %s\n", model);
#endif

        return checkboard();
}

For zynqmp.c:

int checkboard(void)
{
        puts("Board: Xilinx ZynqMP\n");
        return 0;
}

Some arches and boards, not Zynq.

#ifdef CONFIG_ARCH_MISC_INIT
        arch_misc_init,
#endif

#ifdef CONFIG_MISC_INIT_R
        misc_init_r,
#endif

#ifdef CONFIG_ARM
static int initr_enable_interrupts(void)
{
        enable_interrupts();
        return 0;
}
#endif

From arch/arm/lib/interrupts.c:

int interrupt_init (void)
{
        /*
         * setup up stacks if necessary
         */
        IRQ_STACK_START_IN = gd->irq_sp + 8;

        return 0;
}

void enable_interrupts (void)
{
        return;
}
int disable_interrupts (void)
{
        return 0;
}

#ifdef CONFIG_CMD_NET
        initr_ethaddr,
#endif

#ifdef CONFIG_CMD_NET
static int initr_ethaddr(void)
{
        bd_t *bd = gd->bd;

        /* kept around for legacy kernels only ... ignore the next section */
        eth_env_get_enetaddr("ethaddr", bd->bi_enetaddr);
#ifdef CONFIG_HAS_ETH1
        eth_env_get_enetaddr("eth1addr", bd->bi_enet1addr);
#endif
#ifdef CONFIG_HAS_ETH2
        eth_env_get_enetaddr("eth2addr", bd->bi_enet2addr);
#endif
#ifdef CONFIG_HAS_ETH3
        eth_env_get_enetaddr("eth3addr", bd->bi_enet3addr);
#endif
#ifdef CONFIG_HAS_ETH4
        eth_env_get_enetaddr("eth4addr", bd->bi_enet4addr);
#endif
#ifdef CONFIG_HAS_ETH5
        eth_env_get_enetaddr("eth5addr", bd->bi_enet5addr);
#endif
        return 0;
}
#endif /* CONFIG_CMD_NET */

(Defined in board/xilinx/zynq/board.c.)

#ifdef CONFIG_BOARD_LATE_INIT
        board_late_init,
#endif

#ifdef CONFIG_CMD_NET
static int initr_net(void)
{
        puts("Net:   ");
        eth_initialize();
#if defined(CONFIG_RESET_PHY_R)
        debug("Reset Ethernet PHY\n");
        reset_phy();
#endif
        return 0;
}
#endif