hw/nvram: NPCM7xx OTP device model

This supports reading and writing OTP fuses and keys. Only fuse reading
has been tested. Protection is not implemented.

Reviewed-by: Avi Fishman <avi.fishman@nuvoton.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Tested-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Tested-by: Alexander Bulekov <alxndr@bu.edu>
Signed-off-by: Havard Skinnemoen <hskinnemoen@google.com>
Message-id: 20200911052101.2602693-9-hskinnemoen@google.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

hw/arm/npcm7xx.c

@@ -34,6 +34,10 @@
 #define NPCM7XX_MMIO_BA         (0x80000000)
 #define NPCM7XX_MMIO_SZ         (0x7ffd0000)
 
+/* OTP key storage and fuse strap array */
+#define NPCM7XX_OTP1_BA         (0xf0189000)
+#define NPCM7XX_OTP2_BA         (0xf018a000)
+
 /* Core system modules. */
 #define NPCM7XX_L2C_BA          (0xf03fc000)
 #define NPCM7XX_CPUP_BA         (0xf03fe000)
@@ -144,6 +148,20 @@ void npcm7xx_load_kernel(MachineState *machine, NPCM7xxState *soc)
     arm_load_kernel(&soc->cpu[0], machine, &npcm7xx_binfo);
 }
 
+static void npcm7xx_init_fuses(NPCM7xxState *s)
+{
+    NPCM7xxClass *nc = NPCM7XX_GET_CLASS(s);
+    uint32_t value;
+
+    /*
+     * The initial mask of disabled modules indicates the chip derivative (e.g.
+     * NPCM750 or NPCM730).
+     */
+    value = tswap32(nc->disabled_modules);
+    npcm7xx_otp_array_write(&s->fuse_array, &value, NPCM7XX_FUSE_DERIVATIVE,
+                            sizeof(value));
+}
+
 static qemu_irq npcm7xx_irq(NPCM7xxState *s, int n)
 {
     return qdev_get_gpio_in(DEVICE(&s->a9mpcore), n);
@@ -164,6 +182,10 @@ static void npcm7xx_init(Object *obj)
     object_property_add_alias(obj, "power-on-straps", OBJECT(&s->gcr),
                               "power-on-straps");
     object_initialize_child(obj, "clk", &s->clk, TYPE_NPCM7XX_CLK);
+    object_initialize_child(obj, "otp1", &s->key_storage,
+                            TYPE_NPCM7XX_KEY_STORAGE);
+    object_initialize_child(obj, "otp2", &s->fuse_array,
+                            TYPE_NPCM7XX_FUSE_ARRAY);
 
     for (i = 0; i < ARRAY_SIZE(s->tim); i++) {
         object_initialize_child(obj, "tim[*]", &s->tim[i], TYPE_NPCM7XX_TIMER);
@@ -232,6 +254,13 @@ static void npcm7xx_realize(DeviceState *dev, Error **errp)
     sysbus_realize(SYS_BUS_DEVICE(&s->clk), &error_abort);
     sysbus_mmio_map(SYS_BUS_DEVICE(&s->clk), 0, NPCM7XX_CLK_BA);
 
+    /* OTP key storage and fuse strap array. Cannot fail. */
+    sysbus_realize(SYS_BUS_DEVICE(&s->key_storage), &error_abort);
+    sysbus_mmio_map(SYS_BUS_DEVICE(&s->key_storage), 0, NPCM7XX_OTP1_BA);
+    sysbus_realize(SYS_BUS_DEVICE(&s->fuse_array), &error_abort);
+    sysbus_mmio_map(SYS_BUS_DEVICE(&s->fuse_array), 0, NPCM7XX_OTP2_BA);
+    npcm7xx_init_fuses(s);
+
     /* Timer Modules (TIM). Cannot fail. */
     QEMU_BUILD_BUG_ON(ARRAY_SIZE(npcm7xx_tim_addr) != ARRAY_SIZE(s->tim));
     for (i = 0; i < ARRAY_SIZE(s->tim); i++) {

hw/nvram/meson.build

@@ -4,6 +4,7 @@ softmmu_ss.add(when: 'CONFIG_DS1225Y', if_true: files('ds1225y.c'))
 softmmu_ss.add(when: 'CONFIG_NMC93XX_EEPROM', if_true: files('eeprom93xx.c'))
 softmmu_ss.add(when: 'CONFIG_AT24C', if_true: files('eeprom_at24c.c'))
 softmmu_ss.add(when: 'CONFIG_MAC_NVRAM', if_true: files('mac_nvram.c'))
+softmmu_ss.add(when: 'CONFIG_NPCM7XX', if_true: files('npcm7xx_otp.c'))
 softmmu_ss.add(when: 'CONFIG_NRF51_SOC', if_true: files('nrf51_nvm.c'))
 
 specific_ss.add(when: 'CONFIG_PSERIES', if_true: files('spapr_nvram.c'))

hw/nvram/npcm7xx_otp.c

@@ -0,0 +1,440 @@
+/*
+ * Nuvoton NPCM7xx OTP (Fuse Array) Interface
+ *
+ * Copyright 2020 Google LLC
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the
+ * Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * 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.
+ */
+
+#include "qemu/osdep.h"
+
+#include "hw/nvram/npcm7xx_otp.h"
+#include "migration/vmstate.h"
+#include "qapi/error.h"
+#include "qemu/bitops.h"
+#include "qemu/log.h"
+#include "qemu/module.h"
+#include "qemu/units.h"
+
+/* Each module has 4 KiB of register space. Only a fraction of it is used. */
+#define NPCM7XX_OTP_REGS_SIZE (4 * KiB)
+
+/* 32-bit register indices. */
+typedef enum NPCM7xxOTPRegister {
+    NPCM7XX_OTP_FST,
+    NPCM7XX_OTP_FADDR,
+    NPCM7XX_OTP_FDATA,
+    NPCM7XX_OTP_FCFG,
+    /* Offset 0x10 is FKEYIND in OTP1, FUSTRAP in OTP2 */
+    NPCM7XX_OTP_FKEYIND = 0x0010 / sizeof(uint32_t),
+    NPCM7XX_OTP_FUSTRAP = 0x0010 / sizeof(uint32_t),
+    NPCM7XX_OTP_FCTL,
+    NPCM7XX_OTP_REGS_END,
+} NPCM7xxOTPRegister;
+
+/* Register field definitions. */
+#define FST_RIEN BIT(2)
+#define FST_RDST BIT(1)
+#define FST_RDY BIT(0)
+#define FST_RO_MASK (FST_RDST | FST_RDY)
+
+#define FADDR_BYTEADDR(rv) extract32((rv), 0, 10)
+#define FADDR_BITPOS(rv) extract32((rv), 10, 3)
+
+#define FDATA_CLEAR 0x00000001
+
+#define FCFG_FDIS BIT(31)
+#define FCFG_FCFGLK_MASK 0x00ff0000
+
+#define FCTL_PROG_CMD1 0x00000001
+#define FCTL_PROG_CMD2 0xbf79e5d0
+#define FCTL_READ_CMD 0x00000002
+
+/**
+ * struct NPCM7xxOTPClass - OTP module class.
+ * @parent: System bus device class.
+ * @mmio_ops: MMIO register operations for this type of module.
+ *
+ * The two OTP modules (key-storage and fuse-array) have slightly different
+ * behavior, so we give them different MMIO register operations.
+ */
+struct NPCM7xxOTPClass {
+    SysBusDeviceClass parent;
+
+    const MemoryRegionOps *mmio_ops;
+};
+
+#define NPCM7XX_OTP_CLASS(klass) \
+    OBJECT_CLASS_CHECK(NPCM7xxOTPClass, (klass), TYPE_NPCM7XX_OTP)
+#define NPCM7XX_OTP_GET_CLASS(obj) \
+    OBJECT_GET_CLASS(NPCM7xxOTPClass, (obj), TYPE_NPCM7XX_OTP)
+
+static uint8_t ecc_encode_nibble(uint8_t n)
+{
+    uint8_t result = n;
+
+    result |= (((n >> 0) & 1) ^ ((n >> 1) & 1)) << 4;
+    result |= (((n >> 2) & 1) ^ ((n >> 3) & 1)) << 5;
+    result |= (((n >> 0) & 1) ^ ((n >> 2) & 1)) << 6;
+    result |= (((n >> 1) & 1) ^ ((n >> 3) & 1)) << 7;
+
+    return result;
+}
+
+void npcm7xx_otp_array_write(NPCM7xxOTPState *s, const void *data,
+                             unsigned int offset, unsigned int len)
+{
+    const uint8_t *src = data;
+    uint8_t *dst = &s->array[offset];
+
+    while (len-- > 0) {
+        uint8_t c = *src++;
+
+        *dst++ = ecc_encode_nibble(extract8(c, 0, 4));
+        *dst++ = ecc_encode_nibble(extract8(c, 4, 4));
+    }
+}
+
+/* Common register read handler for both OTP classes. */
+static uint64_t npcm7xx_otp_read(NPCM7xxOTPState *s, NPCM7xxOTPRegister reg)
+{
+    uint32_t value = 0;
+
+    switch (reg) {
+    case NPCM7XX_OTP_FST:
+    case NPCM7XX_OTP_FADDR:
+    case NPCM7XX_OTP_FDATA:
+    case NPCM7XX_OTP_FCFG:
+        value = s->regs[reg];
+        break;
+
+    case NPCM7XX_OTP_FCTL:
+        qemu_log_mask(LOG_GUEST_ERROR,
+                      "%s: read from write-only FCTL register\n",
+                      DEVICE(s)->canonical_path);
+        break;
+
+    default:
+        qemu_log_mask(LOG_GUEST_ERROR, "%s: read from invalid offset 0x%zx\n",
+                      DEVICE(s)->canonical_path, reg * sizeof(uint32_t));
+        break;
+    }
+
+    return value;
+}
+
+/* Read a byte from the OTP array into the data register. */
+static void npcm7xx_otp_read_array(NPCM7xxOTPState *s)
+{
+    uint32_t faddr = s->regs[NPCM7XX_OTP_FADDR];
+
+    s->regs[NPCM7XX_OTP_FDATA] = s->array[FADDR_BYTEADDR(faddr)];
+    s->regs[NPCM7XX_OTP_FST] |= FST_RDST | FST_RDY;
+}
+
+/* Program a byte from the data register into the OTP array. */
+static void npcm7xx_otp_program_array(NPCM7xxOTPState *s)
+{
+    uint32_t faddr = s->regs[NPCM7XX_OTP_FADDR];
+
+    /* Bits can only go 0->1, never 1->0. */
+    s->array[FADDR_BYTEADDR(faddr)] |= (1U << FADDR_BITPOS(faddr));
+    s->regs[NPCM7XX_OTP_FST] |= FST_RDST | FST_RDY;
+}
+
+/* Compute the next value of the FCFG register. */
+static uint32_t npcm7xx_otp_compute_fcfg(uint32_t cur_value, uint32_t new_value)
+{
+    uint32_t lock_mask;
+    uint32_t value;
+
+    /*
+     * FCFGLK holds sticky bits 16..23, indicating which bits in FPRGLK (8..15)
+     * and FRDLK (0..7) that are read-only.
+     */
+    lock_mask = (cur_value & FCFG_FCFGLK_MASK) >> 8;
+    lock_mask |= lock_mask >> 8;
+    /* FDIS and FCFGLK bits are sticky (write 1 to set; can't clear). */
+    value = cur_value & (FCFG_FDIS | FCFG_FCFGLK_MASK);
+    /* Preserve read-only bits in FPRGLK and FRDLK */
+    value |= cur_value & lock_mask;
+    /* Set all bits that aren't read-only. */
+    value |= new_value & ~lock_mask;
+
+    return value;
+}
+
+/* Common register write handler for both OTP classes. */
+static void npcm7xx_otp_write(NPCM7xxOTPState *s, NPCM7xxOTPRegister reg,
+                              uint32_t value)
+{
+    switch (reg) {
+    case NPCM7XX_OTP_FST:
+        /* RDST is cleared by writing 1 to it. */
+        if (value & FST_RDST) {
+            s->regs[NPCM7XX_OTP_FST] &= ~FST_RDST;
+        }
+        /* Preserve read-only and write-one-to-clear bits */
+        value &= ~FST_RO_MASK;
+        value |= s->regs[NPCM7XX_OTP_FST] & FST_RO_MASK;
+        break;
+
+    case NPCM7XX_OTP_FADDR:
+        break;
+
+    case NPCM7XX_OTP_FDATA:
+        /*
+         * This register is cleared by writing a magic value to it; no other
+         * values can be written.
+         */
+        if (value == FDATA_CLEAR) {
+            value = 0;
+        } else {
+            value = s->regs[NPCM7XX_OTP_FDATA];
+        }
+        break;
+
+    case NPCM7XX_OTP_FCFG:
+        value = npcm7xx_otp_compute_fcfg(s->regs[NPCM7XX_OTP_FCFG], value);
+        break;
+
+    case NPCM7XX_OTP_FCTL:
+        switch (value) {
+        case FCTL_READ_CMD:
+            npcm7xx_otp_read_array(s);
+            break;
+
+        case FCTL_PROG_CMD1:
+            /*
+             * Programming requires writing two separate magic values to this
+             * register; this is the first one. Just store it so it can be
+             * verified later when the second magic value is received.
+             */
+            break;
+
+        case FCTL_PROG_CMD2:
+            /*
+             * Only initiate programming if we received the first half of the
+             * command immediately before this one.
+             */
+            if (s->regs[NPCM7XX_OTP_FCTL] == FCTL_PROG_CMD1) {
+                npcm7xx_otp_program_array(s);
+            }
+            break;
+
+        default:
+            qemu_log_mask(LOG_GUEST_ERROR,
+                          "%s: unrecognized FCNTL value 0x%" PRIx32 "\n",
+                          DEVICE(s)->canonical_path, value);
+            break;
+        }
+        if (value != FCTL_PROG_CMD1) {
+            value = 0;
+        }
+        break;
+
+    default:
+        qemu_log_mask(LOG_GUEST_ERROR, "%s: write to invalid offset 0x%zx\n",
+                      DEVICE(s)->canonical_path, reg * sizeof(uint32_t));
+        return;
+    }
+
+    s->regs[reg] = value;
+}
+
+/* Register read handler specific to the fuse array OTP module. */
+static uint64_t npcm7xx_fuse_array_read(void *opaque, hwaddr addr,
+                                        unsigned int size)
+{
+    NPCM7xxOTPRegister reg = addr / sizeof(uint32_t);
+    NPCM7xxOTPState *s = opaque;
+    uint32_t value;
+
+    /*
+     * Only the Fuse Strap register needs special handling; all other registers
+     * work the same way for both kinds of OTP modules.
+     */
+    if (reg != NPCM7XX_OTP_FUSTRAP) {
+        value = npcm7xx_otp_read(s, reg);
+    } else {
+        /* FUSTRAP is stored as three copies in the OTP array. */
+        uint32_t fustrap[3];
+
+        memcpy(fustrap, &s->array[0], sizeof(fustrap));
+
+        /* Determine value by a majority vote on each bit. */
+        value = (fustrap[0] & fustrap[1]) | (fustrap[0] & fustrap[2]) |
+                (fustrap[1] & fustrap[2]);
+    }
+
+    return value;
+}
+
+/* Register write handler specific to the fuse array OTP module. */
+static void npcm7xx_fuse_array_write(void *opaque, hwaddr addr, uint64_t v,
+                                     unsigned int size)
+{
+    NPCM7xxOTPRegister reg = addr / sizeof(uint32_t);
+    NPCM7xxOTPState *s = opaque;
+
+    /*
+     * The Fuse Strap register is read-only. Other registers are handled by
+     * common code.
+     */
+    if (reg != NPCM7XX_OTP_FUSTRAP) {
+        npcm7xx_otp_write(s, reg, v);
+    }
+}
+
+static const MemoryRegionOps npcm7xx_fuse_array_ops = {
+    .read       = npcm7xx_fuse_array_read,
+    .write      = npcm7xx_fuse_array_write,
+    .endianness = DEVICE_LITTLE_ENDIAN,
+    .valid      = {
+        .min_access_size        = 4,
+        .max_access_size        = 4,
+        .unaligned              = false,
+    },
+};
+
+/* Register read handler specific to the key storage OTP module. */
+static uint64_t npcm7xx_key_storage_read(void *opaque, hwaddr addr,
+                                         unsigned int size)
+{
+    NPCM7xxOTPRegister reg = addr / sizeof(uint32_t);
+    NPCM7xxOTPState *s = opaque;
+
+    /*
+     * Only the Fuse Key Index register needs special handling; all other
+     * registers work the same way for both kinds of OTP modules.
+     */
+    if (reg != NPCM7XX_OTP_FKEYIND) {
+        return npcm7xx_otp_read(s, reg);
+    }
+
+    qemu_log_mask(LOG_UNIMP, "%s: FKEYIND is not implemented\n", __func__);
+
+    return s->regs[NPCM7XX_OTP_FKEYIND];
+}
+
+/* Register write handler specific to the key storage OTP module. */
+static void npcm7xx_key_storage_write(void *opaque, hwaddr addr, uint64_t v,
+                                      unsigned int size)
+{
+    NPCM7xxOTPRegister reg = addr / sizeof(uint32_t);
+    NPCM7xxOTPState *s = opaque;
+
+    /*
+     * Only the Fuse Key Index register needs special handling; all other
+     * registers work the same way for both kinds of OTP modules.
+     */
+    if (reg != NPCM7XX_OTP_FKEYIND) {
+        npcm7xx_otp_write(s, reg, v);
+        return;
+    }
+
+    qemu_log_mask(LOG_UNIMP, "%s: FKEYIND is not implemented\n", __func__);
+
+    s->regs[NPCM7XX_OTP_FKEYIND] = v;
+}
+
+static const MemoryRegionOps npcm7xx_key_storage_ops = {
+    .read       = npcm7xx_key_storage_read,
+    .write      = npcm7xx_key_storage_write,
+    .endianness = DEVICE_LITTLE_ENDIAN,
+    .valid      = {
+        .min_access_size        = 4,
+        .max_access_size        = 4,
+        .unaligned              = false,
+    },
+};
+
+static void npcm7xx_otp_enter_reset(Object *obj, ResetType type)
+{
+    NPCM7xxOTPState *s = NPCM7XX_OTP(obj);
+
+    memset(s->regs, 0, sizeof(s->regs));
+
+    s->regs[NPCM7XX_OTP_FST] = 0x00000001;
+    s->regs[NPCM7XX_OTP_FCFG] = 0x20000000;
+}
+
+static void npcm7xx_otp_realize(DeviceState *dev, Error **errp)
+{
+    NPCM7xxOTPClass *oc = NPCM7XX_OTP_GET_CLASS(dev);
+    NPCM7xxOTPState *s = NPCM7XX_OTP(dev);
+    SysBusDevice *sbd = &s->parent;
+
+    memset(s->array, 0, sizeof(s->array));
+
+    memory_region_init_io(&s->mmio, OBJECT(s), oc->mmio_ops, s, "regs",
+                          NPCM7XX_OTP_REGS_SIZE);
+    sysbus_init_mmio(sbd, &s->mmio);
+}
+
+static const VMStateDescription vmstate_npcm7xx_otp = {
+    .name = "npcm7xx-otp",
+    .version_id = 0,
+    .minimum_version_id = 0,
+    .fields = (VMStateField[]) {
+        VMSTATE_UINT32_ARRAY(regs, NPCM7xxOTPState, NPCM7XX_OTP_NR_REGS),
+        VMSTATE_UINT8_ARRAY(array, NPCM7xxOTPState, NPCM7XX_OTP_ARRAY_BYTES),
+        VMSTATE_END_OF_LIST(),
+    },
+};
+
+static void npcm7xx_otp_class_init(ObjectClass *klass, void *data)
+{
+    ResettableClass *rc = RESETTABLE_CLASS(klass);
+    DeviceClass *dc = DEVICE_CLASS(klass);
+
+    QEMU_BUILD_BUG_ON(NPCM7XX_OTP_REGS_END > NPCM7XX_OTP_NR_REGS);
+
+    dc->realize = npcm7xx_otp_realize;
+    dc->vmsd = &vmstate_npcm7xx_otp;
+    rc->phases.enter = npcm7xx_otp_enter_reset;
+}
+
+static void npcm7xx_key_storage_class_init(ObjectClass *klass, void *data)
+{
+    NPCM7xxOTPClass *oc = NPCM7XX_OTP_CLASS(klass);
+
+    oc->mmio_ops = &npcm7xx_key_storage_ops;
+}
+
+static void npcm7xx_fuse_array_class_init(ObjectClass *klass, void *data)
+{
+    NPCM7xxOTPClass *oc = NPCM7XX_OTP_CLASS(klass);
+
+    oc->mmio_ops = &npcm7xx_fuse_array_ops;
+}
+
+static const TypeInfo npcm7xx_otp_types[] = {
+    {
+        .name = TYPE_NPCM7XX_OTP,
+        .parent = TYPE_SYS_BUS_DEVICE,
+        .instance_size = sizeof(NPCM7xxOTPState),
+        .class_size = sizeof(NPCM7xxOTPClass),
+        .class_init = npcm7xx_otp_class_init,
+        .abstract = true,
+    },
+    {
+        .name = TYPE_NPCM7XX_KEY_STORAGE,
+        .parent = TYPE_NPCM7XX_OTP,
+        .class_init = npcm7xx_key_storage_class_init,
+    },
+    {
+        .name = TYPE_NPCM7XX_FUSE_ARRAY,
+        .parent = TYPE_NPCM7XX_OTP,
+        .class_init = npcm7xx_fuse_array_class_init,
+    },
+};
+DEFINE_TYPES(npcm7xx_otp_types);

include/hw/arm/npcm7xx.h

@@ -20,6 +20,7 @@
 #include "hw/cpu/a9mpcore.h"
 #include "hw/misc/npcm7xx_clk.h"
 #include "hw/misc/npcm7xx_gcr.h"
+#include "hw/nvram/npcm7xx_otp.h"
 #include "hw/timer/npcm7xx_timer.h"
 #include "target/arm/cpu.h"
 
@@ -68,6 +69,8 @@ typedef struct NPCM7xxState {
     NPCM7xxGCRState     gcr;
     NPCM7xxCLKState     clk;
     NPCM7xxTimerCtrlState tim[3];
+    NPCM7xxOTPState     key_storage;
+    NPCM7xxOTPState     fuse_array;
 } NPCM7xxState;
 
 #define TYPE_NPCM7XX    "npcm7xx"

include/hw/nvram/npcm7xx_otp.h

@@ -0,0 +1,79 @@
+/*
+ * Nuvoton NPCM7xx OTP (Fuse Array) Interface
+ *
+ * Copyright 2020 Google LLC
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the
+ * Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * 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.
+ */
+#ifndef NPCM7XX_OTP_H
+#define NPCM7XX_OTP_H
+
+#include "exec/memory.h"
+#include "hw/sysbus.h"
+
+/* Each OTP module holds 8192 bits of one-time programmable storage */
+#define NPCM7XX_OTP_ARRAY_BITS (8192)
+#define NPCM7XX_OTP_ARRAY_BYTES (NPCM7XX_OTP_ARRAY_BITS / BITS_PER_BYTE)
+
+/* Fuse array offsets */
+#define NPCM7XX_FUSE_FUSTRAP (0)
+#define NPCM7XX_FUSE_CP_FUSTRAP (12)
+#define NPCM7XX_FUSE_DAC_CALIB (16)
+#define NPCM7XX_FUSE_ADC_CALIB (24)
+#define NPCM7XX_FUSE_DERIVATIVE (64)
+#define NPCM7XX_FUSE_TEST_SIG (72)
+#define NPCM7XX_FUSE_DIE_LOCATION (74)
+#define NPCM7XX_FUSE_GP1 (80)
+#define NPCM7XX_FUSE_GP2 (128)
+
+/*
+ * Number of registers in our device state structure. Don't change this without
+ * incrementing the version_id in the vmstate.
+ */
+#define NPCM7XX_OTP_NR_REGS (0x18 / sizeof(uint32_t))
+
+/**
+ * struct NPCM7xxOTPState - Device state for one OTP module.
+ * @parent: System bus device.
+ * @mmio: Memory region through which registers are accessed.
+ * @regs: Register contents.
+ * @array: OTP storage array.
+ */
+typedef struct NPCM7xxOTPState {
+    SysBusDevice parent;
+
+    MemoryRegion mmio;
+    uint32_t regs[NPCM7XX_OTP_NR_REGS];
+    uint8_t array[NPCM7XX_OTP_ARRAY_BYTES];
+} NPCM7xxOTPState;
+
+#define TYPE_NPCM7XX_OTP "npcm7xx-otp"
+#define NPCM7XX_OTP(obj) OBJECT_CHECK(NPCM7xxOTPState, (obj), TYPE_NPCM7XX_OTP)
+
+#define TYPE_NPCM7XX_KEY_STORAGE "npcm7xx-key-storage"
+#define TYPE_NPCM7XX_FUSE_ARRAY "npcm7xx-fuse-array"
+
+typedef struct NPCM7xxOTPClass NPCM7xxOTPClass;
+
+/**
+ * npcm7xx_otp_array_write - ECC encode and write data to OTP array.
+ * @s: OTP module.
+ * @data: Data to be encoded and written.
+ * @offset: Offset of first byte to be written in the OTP array.
+ * @len: Number of bytes before ECC encoding.
+ *
+ * Each nibble of data is encoded into a byte, so the number of bytes written
+ * to the array will be @len * 2.
+ */
+extern void npcm7xx_otp_array_write(NPCM7xxOTPState *s, const void *data,
+                                    unsigned int offset, unsigned int len);
+
+#endif /* NPCM7XX_OTP_H */