hw/i2c: Implement NPCM7XX SMBus Module Single Mode

This commit implements the single-byte mode of the SMBus.

Each Nuvoton SoC has 16 System Management Bus (SMBus). These buses
compliant with SMBus and I2C protocol.

This patch implements the single-byte mode of the SMBus. In this mode,
the user sends or receives a byte each time. The SMBus device transmits
it to the underlying i2c device and sends an interrupt back to the QEMU
guest.

Reviewed-by: Doug Evans<dje@google.com>
Reviewed-by: Tyrong Ting<kfting@nuvoton.com>
Signed-off-by: Hao Wu <wuhaotsh@google.com>
Reviewed-by: Corey Minyard <cminyard@mvista.com>
Message-id: 20210210220426.3577804-2-wuhaotsh@google.com
Acked-by: Corey Minyard <cminyard@mvista.com>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

1 files changed, 783 insertions, 0 deletions

diff --git a/hw/i2c/npcm7xx_smbus.c b/hw/i2c/npcm7xx_smbus.c
new file mode 100644
index 0000000..a465740
--- /dev/null
+++ b/hw/i2c/npcm7xx_smbus.c
@@ -0,0 +1,783 @@
+/*
+ * Nuvoton NPCM7xx SMBus Module.
+ *
+ * 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/i2c/npcm7xx_smbus.h"
+#include "migration/vmstate.h"
+#include "qemu/bitops.h"
+#include "qemu/guest-random.h"
+#include "qemu/log.h"
+#include "qemu/module.h"
+#include "qemu/units.h"
+
+#include "trace.h"
+
+enum NPCM7xxSMBusCommonRegister {
+    NPCM7XX_SMB_SDA     = 0x0,
+    NPCM7XX_SMB_ST      = 0x2,
+    NPCM7XX_SMB_CST     = 0x4,
+    NPCM7XX_SMB_CTL1    = 0x6,
+    NPCM7XX_SMB_ADDR1   = 0x8,
+    NPCM7XX_SMB_CTL2    = 0xa,
+    NPCM7XX_SMB_ADDR2   = 0xc,
+    NPCM7XX_SMB_CTL3    = 0xe,
+    NPCM7XX_SMB_CST2    = 0x18,
+    NPCM7XX_SMB_CST3    = 0x19,
+    NPCM7XX_SMB_VER     = 0x1f,
+};
+
+enum NPCM7xxSMBusBank0Register {
+    NPCM7XX_SMB_ADDR3   = 0x10,
+    NPCM7XX_SMB_ADDR7   = 0x11,
+    NPCM7XX_SMB_ADDR4   = 0x12,
+    NPCM7XX_SMB_ADDR8   = 0x13,
+    NPCM7XX_SMB_ADDR5   = 0x14,
+    NPCM7XX_SMB_ADDR9   = 0x15,
+    NPCM7XX_SMB_ADDR6   = 0x16,
+    NPCM7XX_SMB_ADDR10  = 0x17,
+    NPCM7XX_SMB_CTL4    = 0x1a,
+    NPCM7XX_SMB_CTL5    = 0x1b,
+    NPCM7XX_SMB_SCLLT   = 0x1c,
+    NPCM7XX_SMB_FIF_CTL = 0x1d,
+    NPCM7XX_SMB_SCLHT   = 0x1e,
+};
+
+enum NPCM7xxSMBusBank1Register {
+    NPCM7XX_SMB_FIF_CTS  = 0x10,
+    NPCM7XX_SMB_FAIR_PER = 0x11,
+    NPCM7XX_SMB_TXF_CTL  = 0x12,
+    NPCM7XX_SMB_T_OUT    = 0x14,
+    NPCM7XX_SMB_TXF_STS  = 0x1a,
+    NPCM7XX_SMB_RXF_STS  = 0x1c,
+    NPCM7XX_SMB_RXF_CTL  = 0x1e,
+};
+
+/* ST fields */
+#define NPCM7XX_SMBST_STP           BIT(7)
+#define NPCM7XX_SMBST_SDAST         BIT(6)
+#define NPCM7XX_SMBST_BER           BIT(5)
+#define NPCM7XX_SMBST_NEGACK        BIT(4)
+#define NPCM7XX_SMBST_STASTR        BIT(3)
+#define NPCM7XX_SMBST_NMATCH        BIT(2)
+#define NPCM7XX_SMBST_MODE          BIT(1)
+#define NPCM7XX_SMBST_XMIT          BIT(0)
+
+/* CST fields */
+#define NPCM7XX_SMBCST_ARPMATCH        BIT(7)
+#define NPCM7XX_SMBCST_MATCHAF         BIT(6)
+#define NPCM7XX_SMBCST_TGSCL           BIT(5)
+#define NPCM7XX_SMBCST_TSDA            BIT(4)
+#define NPCM7XX_SMBCST_GCMATCH         BIT(3)
+#define NPCM7XX_SMBCST_MATCH           BIT(2)
+#define NPCM7XX_SMBCST_BB              BIT(1)
+#define NPCM7XX_SMBCST_BUSY            BIT(0)
+
+/* CST2 fields */
+#define NPCM7XX_SMBCST2_INTSTS         BIT(7)
+#define NPCM7XX_SMBCST2_MATCH7F        BIT(6)
+#define NPCM7XX_SMBCST2_MATCH6F        BIT(5)
+#define NPCM7XX_SMBCST2_MATCH5F        BIT(4)
+#define NPCM7XX_SMBCST2_MATCH4F        BIT(3)
+#define NPCM7XX_SMBCST2_MATCH3F        BIT(2)
+#define NPCM7XX_SMBCST2_MATCH2F        BIT(1)
+#define NPCM7XX_SMBCST2_MATCH1F        BIT(0)
+
+/* CST3 fields */
+#define NPCM7XX_SMBCST3_EO_BUSY        BIT(7)
+#define NPCM7XX_SMBCST3_MATCH10F       BIT(2)
+#define NPCM7XX_SMBCST3_MATCH9F        BIT(1)
+#define NPCM7XX_SMBCST3_MATCH8F        BIT(0)
+
+/* CTL1 fields */
+#define NPCM7XX_SMBCTL1_STASTRE     BIT(7)
+#define NPCM7XX_SMBCTL1_NMINTE      BIT(6)
+#define NPCM7XX_SMBCTL1_GCMEN       BIT(5)
+#define NPCM7XX_SMBCTL1_ACK         BIT(4)
+#define NPCM7XX_SMBCTL1_EOBINTE     BIT(3)
+#define NPCM7XX_SMBCTL1_INTEN       BIT(2)
+#define NPCM7XX_SMBCTL1_STOP        BIT(1)
+#define NPCM7XX_SMBCTL1_START       BIT(0)
+
+/* CTL2 fields */
+#define NPCM7XX_SMBCTL2_SCLFRQ(rv)  extract8((rv), 1, 6)
+#define NPCM7XX_SMBCTL2_ENABLE      BIT(0)
+
+/* CTL3 fields */
+#define NPCM7XX_SMBCTL3_SCL_LVL     BIT(7)
+#define NPCM7XX_SMBCTL3_SDA_LVL     BIT(6)
+#define NPCM7XX_SMBCTL3_BNK_SEL     BIT(5)
+#define NPCM7XX_SMBCTL3_400K_MODE   BIT(4)
+#define NPCM7XX_SMBCTL3_IDL_START   BIT(3)
+#define NPCM7XX_SMBCTL3_ARPMEN      BIT(2)
+#define NPCM7XX_SMBCTL3_SCLFRQ(rv)  extract8((rv), 0, 2)
+
+/* ADDR fields */
+#define NPCM7XX_ADDR_EN             BIT(7)
+#define NPCM7XX_ADDR_A(rv)          extract8((rv), 0, 6)
+
+#define KEEP_OLD_BIT(o, n, b)       (((n) & (~(b))) | ((o) & (b)))
+#define WRITE_ONE_CLEAR(o, n, b)    ((n) & (b) ? (o) & (~(b)) : (o))
+
+#define NPCM7XX_SMBUS_ENABLED(s)    ((s)->ctl2 & NPCM7XX_SMBCTL2_ENABLE)
+
+/* VERSION fields values, read-only. */
+#define NPCM7XX_SMBUS_VERSION_NUMBER 1
+#define NPCM7XX_SMBUS_VERSION_FIFO_SUPPORTED 0
+
+/* Reset values */
+#define NPCM7XX_SMB_ST_INIT_VAL     0x00
+#define NPCM7XX_SMB_CST_INIT_VAL    0x10
+#define NPCM7XX_SMB_CST2_INIT_VAL   0x00
+#define NPCM7XX_SMB_CST3_INIT_VAL   0x00
+#define NPCM7XX_SMB_CTL1_INIT_VAL   0x00
+#define NPCM7XX_SMB_CTL2_INIT_VAL   0x00
+#define NPCM7XX_SMB_CTL3_INIT_VAL   0xc0
+#define NPCM7XX_SMB_CTL4_INIT_VAL   0x07
+#define NPCM7XX_SMB_CTL5_INIT_VAL   0x00
+#define NPCM7XX_SMB_ADDR_INIT_VAL   0x00
+#define NPCM7XX_SMB_SCLLT_INIT_VAL  0x00
+#define NPCM7XX_SMB_SCLHT_INIT_VAL  0x00
+
+static uint8_t npcm7xx_smbus_get_version(void)
+{
+    return NPCM7XX_SMBUS_VERSION_FIFO_SUPPORTED << 7 |
+           NPCM7XX_SMBUS_VERSION_NUMBER;
+}
+
+static void npcm7xx_smbus_update_irq(NPCM7xxSMBusState *s)
+{
+    int level;
+
+    if (s->ctl1 & NPCM7XX_SMBCTL1_INTEN) {
+        level = !!((s->ctl1 & NPCM7XX_SMBCTL1_NMINTE &&
+                    s->st & NPCM7XX_SMBST_NMATCH) ||
+                   (s->st & NPCM7XX_SMBST_BER) ||
+                   (s->st & NPCM7XX_SMBST_NEGACK) ||
+                   (s->st & NPCM7XX_SMBST_SDAST) ||
+                   (s->ctl1 & NPCM7XX_SMBCTL1_STASTRE &&
+                    s->st & NPCM7XX_SMBST_SDAST) ||
+                   (s->ctl1 & NPCM7XX_SMBCTL1_EOBINTE &&
+                    s->cst3 & NPCM7XX_SMBCST3_EO_BUSY));
+
+        if (level) {
+            s->cst2 |= NPCM7XX_SMBCST2_INTSTS;
+        } else {
+            s->cst2 &= ~NPCM7XX_SMBCST2_INTSTS;
+        }
+        qemu_set_irq(s->irq, level);
+    }
+}
+
+static void npcm7xx_smbus_nack(NPCM7xxSMBusState *s)
+{
+    s->st &= ~NPCM7XX_SMBST_SDAST;
+    s->st |= NPCM7XX_SMBST_NEGACK;
+    s->status = NPCM7XX_SMBUS_STATUS_NEGACK;
+}
+
+static void npcm7xx_smbus_send_byte(NPCM7xxSMBusState *s, uint8_t value)
+{
+    int rv = i2c_send(s->bus, value);
+
+    if (rv) {
+        npcm7xx_smbus_nack(s);
+    } else {
+        s->st |= NPCM7XX_SMBST_SDAST;
+    }
+    trace_npcm7xx_smbus_send_byte((DEVICE(s)->canonical_path), value, !rv);
+    npcm7xx_smbus_update_irq(s);
+}
+
+static void npcm7xx_smbus_recv_byte(NPCM7xxSMBusState *s)
+{
+    s->sda = i2c_recv(s->bus);
+    s->st |= NPCM7XX_SMBST_SDAST;
+    if (s->st & NPCM7XX_SMBCTL1_ACK) {
+        trace_npcm7xx_smbus_nack(DEVICE(s)->canonical_path);
+        i2c_nack(s->bus);
+        s->st &= NPCM7XX_SMBCTL1_ACK;
+    }
+    trace_npcm7xx_smbus_recv_byte((DEVICE(s)->canonical_path), s->sda);
+    npcm7xx_smbus_update_irq(s);
+}
+
+static void npcm7xx_smbus_start(NPCM7xxSMBusState *s)
+{
+    /*
+     * We can start the bus if one of these is true:
+     * 1. The bus is idle (so we can request it)
+     * 2. We are the occupier (it's a repeated start condition.)
+     */
+    int available = !i2c_bus_busy(s->bus) ||
+                    s->status != NPCM7XX_SMBUS_STATUS_IDLE;
+
+    if (available) {
+        s->st |= NPCM7XX_SMBST_MODE | NPCM7XX_SMBST_XMIT | NPCM7XX_SMBST_SDAST;
+        s->cst |= NPCM7XX_SMBCST_BUSY;
+    } else {
+        s->st &= ~NPCM7XX_SMBST_MODE;
+        s->cst &= ~NPCM7XX_SMBCST_BUSY;
+        s->st |= NPCM7XX_SMBST_BER;
+    }
+
+    trace_npcm7xx_smbus_start(DEVICE(s)->canonical_path, available);
+    s->cst |= NPCM7XX_SMBCST_BB;
+    s->status = NPCM7XX_SMBUS_STATUS_IDLE;
+    npcm7xx_smbus_update_irq(s);
+}
+
+static void npcm7xx_smbus_send_address(NPCM7xxSMBusState *s, uint8_t value)
+{
+    int recv;
+    int rv;
+
+    recv = value & BIT(0);
+    rv = i2c_start_transfer(s->bus, value >> 1, recv);
+    trace_npcm7xx_smbus_send_address(DEVICE(s)->canonical_path,
+                                     value >> 1, recv, !rv);
+    if (rv) {
+        qemu_log_mask(LOG_GUEST_ERROR,
+                      "%s: requesting i2c bus for 0x%02x failed: %d\n",
+                      DEVICE(s)->canonical_path, value, rv);
+        /* Failed to start transfer. NACK to reject.*/
+        if (recv) {
+            s->st &= ~NPCM7XX_SMBST_XMIT;
+        } else {
+            s->st |= NPCM7XX_SMBST_XMIT;
+        }
+        npcm7xx_smbus_nack(s);
+        npcm7xx_smbus_update_irq(s);
+        return;
+    }
+
+    s->st &= ~NPCM7XX_SMBST_NEGACK;
+    if (recv) {
+        s->status = NPCM7XX_SMBUS_STATUS_RECEIVING;
+        s->st &= ~NPCM7XX_SMBST_XMIT;
+    } else {
+        s->status = NPCM7XX_SMBUS_STATUS_SENDING;
+        s->st |= NPCM7XX_SMBST_XMIT;
+    }
+
+    if (s->ctl1 & NPCM7XX_SMBCTL1_STASTRE) {
+        s->st |= NPCM7XX_SMBST_STASTR;
+        if (!recv) {
+            s->st |= NPCM7XX_SMBST_SDAST;
+        }
+    } else if (recv) {
+        npcm7xx_smbus_recv_byte(s);
+    }
+    npcm7xx_smbus_update_irq(s);
+}
+
+static void npcm7xx_smbus_execute_stop(NPCM7xxSMBusState *s)
+{
+    i2c_end_transfer(s->bus);
+    s->st = 0;
+    s->cst = 0;
+    s->status = NPCM7XX_SMBUS_STATUS_IDLE;
+    s->cst3 |= NPCM7XX_SMBCST3_EO_BUSY;
+    trace_npcm7xx_smbus_stop(DEVICE(s)->canonical_path);
+    npcm7xx_smbus_update_irq(s);
+}
+
+
+static void npcm7xx_smbus_stop(NPCM7xxSMBusState *s)
+{
+    if (s->st & NPCM7XX_SMBST_MODE) {
+        switch (s->status) {
+        case NPCM7XX_SMBUS_STATUS_RECEIVING:
+        case NPCM7XX_SMBUS_STATUS_STOPPING_LAST_RECEIVE:
+            s->status = NPCM7XX_SMBUS_STATUS_STOPPING_LAST_RECEIVE;
+            break;
+
+        case NPCM7XX_SMBUS_STATUS_NEGACK:
+            s->status = NPCM7XX_SMBUS_STATUS_STOPPING_NEGACK;
+            break;
+
+        default:
+            npcm7xx_smbus_execute_stop(s);
+            break;
+        }
+    }
+}
+
+static uint8_t npcm7xx_smbus_read_sda(NPCM7xxSMBusState *s)
+{
+    uint8_t value = s->sda;
+
+    switch (s->status) {
+    case NPCM7XX_SMBUS_STATUS_STOPPING_LAST_RECEIVE:
+        npcm7xx_smbus_execute_stop(s);
+        break;
+
+    case NPCM7XX_SMBUS_STATUS_RECEIVING:
+        npcm7xx_smbus_recv_byte(s);
+        break;
+
+    default:
+        /* Do nothing */
+        break;
+    }
+
+    return value;
+}
+
+static void npcm7xx_smbus_write_sda(NPCM7xxSMBusState *s, uint8_t value)
+{
+    s->sda = value;
+    if (s->st & NPCM7XX_SMBST_MODE) {
+        switch (s->status) {
+        case NPCM7XX_SMBUS_STATUS_IDLE:
+            npcm7xx_smbus_send_address(s, value);
+            break;
+        case NPCM7XX_SMBUS_STATUS_SENDING:
+            npcm7xx_smbus_send_byte(s, value);
+            break;
+        default:
+            qemu_log_mask(LOG_GUEST_ERROR,
+                          "%s: write to SDA in invalid status %d: %u\n",
+                          DEVICE(s)->canonical_path, s->status, value);
+            break;
+        }
+    }
+}
+
+static void npcm7xx_smbus_write_st(NPCM7xxSMBusState *s, uint8_t value)
+{
+    s->st = WRITE_ONE_CLEAR(s->st, value, NPCM7XX_SMBST_STP);
+    s->st = WRITE_ONE_CLEAR(s->st, value, NPCM7XX_SMBST_BER);
+    s->st = WRITE_ONE_CLEAR(s->st, value, NPCM7XX_SMBST_STASTR);
+    s->st = WRITE_ONE_CLEAR(s->st, value, NPCM7XX_SMBST_NMATCH);
+
+    if (value & NPCM7XX_SMBST_NEGACK) {
+        s->st &= ~NPCM7XX_SMBST_NEGACK;
+        if (s->status == NPCM7XX_SMBUS_STATUS_STOPPING_NEGACK) {
+            npcm7xx_smbus_execute_stop(s);
+        }
+    }
+
+    if (value & NPCM7XX_SMBST_STASTR &&
+            s->status == NPCM7XX_SMBUS_STATUS_RECEIVING) {
+        npcm7xx_smbus_recv_byte(s);
+    }
+
+    npcm7xx_smbus_update_irq(s);
+}
+
+static void npcm7xx_smbus_write_cst(NPCM7xxSMBusState *s, uint8_t value)
+{
+    uint8_t new_value = s->cst;
+
+    s->cst = WRITE_ONE_CLEAR(new_value, value, NPCM7XX_SMBCST_BB);
+    npcm7xx_smbus_update_irq(s);
+}
+
+static void npcm7xx_smbus_write_cst3(NPCM7xxSMBusState *s, uint8_t value)
+{
+    s->cst3 = WRITE_ONE_CLEAR(s->cst3, value, NPCM7XX_SMBCST3_EO_BUSY);
+    npcm7xx_smbus_update_irq(s);
+}
+
+static void npcm7xx_smbus_write_ctl1(NPCM7xxSMBusState *s, uint8_t value)
+{
+    s->ctl1 = KEEP_OLD_BIT(s->ctl1, value,
+            NPCM7XX_SMBCTL1_START | NPCM7XX_SMBCTL1_STOP | NPCM7XX_SMBCTL1_ACK);
+
+    if (value & NPCM7XX_SMBCTL1_START) {
+        npcm7xx_smbus_start(s);
+    }
+
+    if (value & NPCM7XX_SMBCTL1_STOP) {
+        npcm7xx_smbus_stop(s);
+    }
+
+    npcm7xx_smbus_update_irq(s);
+}
+
+static void npcm7xx_smbus_write_ctl2(NPCM7xxSMBusState *s, uint8_t value)
+{
+    s->ctl2 = value;
+
+    if (!NPCM7XX_SMBUS_ENABLED(s)) {
+        /* Disable this SMBus module. */
+        s->ctl1 = 0;
+        s->st = 0;
+        s->cst3 = s->cst3 & (~NPCM7XX_SMBCST3_EO_BUSY);
+        s->cst = 0;
+    }
+}
+
+static void npcm7xx_smbus_write_ctl3(NPCM7xxSMBusState *s, uint8_t value)
+{
+    uint8_t old_ctl3 = s->ctl3;
+
+    /* Write to SDA and SCL bits are ignored. */
+    s->ctl3 =  KEEP_OLD_BIT(old_ctl3, value,
+                            NPCM7XX_SMBCTL3_SCL_LVL | NPCM7XX_SMBCTL3_SDA_LVL);
+}
+
+static uint64_t npcm7xx_smbus_read(void *opaque, hwaddr offset, unsigned size)
+{
+    NPCM7xxSMBusState *s = opaque;
+    uint64_t value = 0;
+    uint8_t bank = s->ctl3 & NPCM7XX_SMBCTL3_BNK_SEL;
+
+    /* The order of the registers are their order in memory. */
+    switch (offset) {
+    case NPCM7XX_SMB_SDA:
+        value = npcm7xx_smbus_read_sda(s);
+        break;
+
+    case NPCM7XX_SMB_ST:
+        value = s->st;
+        break;
+
+    case NPCM7XX_SMB_CST:
+        value = s->cst;
+        break;
+
+    case NPCM7XX_SMB_CTL1:
+        value = s->ctl1;
+        break;
+
+    case NPCM7XX_SMB_ADDR1:
+        value = s->addr[0];
+        break;
+
+    case NPCM7XX_SMB_CTL2:
+        value = s->ctl2;
+        break;
+
+    case NPCM7XX_SMB_ADDR2:
+        value = s->addr[1];
+        break;
+
+    case NPCM7XX_SMB_CTL3:
+        value = s->ctl3;
+        break;
+
+    case NPCM7XX_SMB_CST2:
+        value = s->cst2;
+        break;
+
+    case NPCM7XX_SMB_CST3:
+        value = s->cst3;
+        break;
+
+    case NPCM7XX_SMB_VER:
+        value = npcm7xx_smbus_get_version();
+        break;
+
+    /* This register is either invalid or banked at this point. */
+    default:
+        if (bank) {
+            /* Bank 1 */
+            qemu_log_mask(LOG_GUEST_ERROR,
+                    "%s: read from invalid offset 0x%" HWADDR_PRIx "\n",
+                    DEVICE(s)->canonical_path, offset);
+        } else {
+            /* Bank 0 */
+            switch (offset) {
+            case NPCM7XX_SMB_ADDR3:
+                value = s->addr[2];
+                break;
+
+            case NPCM7XX_SMB_ADDR7:
+                value = s->addr[6];
+                break;
+
+            case NPCM7XX_SMB_ADDR4:
+                value = s->addr[3];
+                break;
+
+            case NPCM7XX_SMB_ADDR8:
+                value = s->addr[7];
+                break;
+
+            case NPCM7XX_SMB_ADDR5:
+                value = s->addr[4];
+                break;
+
+            case NPCM7XX_SMB_ADDR9:
+                value = s->addr[8];
+                break;
+
+            case NPCM7XX_SMB_ADDR6:
+                value = s->addr[5];
+                break;
+
+            case NPCM7XX_SMB_ADDR10:
+                value = s->addr[9];
+                break;
+
+            case NPCM7XX_SMB_CTL4:
+                value = s->ctl4;
+                break;
+
+            case NPCM7XX_SMB_CTL5:
+                value = s->ctl5;
+                break;
+
+            case NPCM7XX_SMB_SCLLT:
+                value = s->scllt;
+                break;
+
+            case NPCM7XX_SMB_SCLHT:
+                value = s->sclht;
+                break;
+
+            default:
+                qemu_log_mask(LOG_GUEST_ERROR,
+                        "%s: read from invalid offset 0x%" HWADDR_PRIx "\n",
+                        DEVICE(s)->canonical_path, offset);
+                break;
+            }
+        }
+        break;
+    }
+
+    trace_npcm7xx_smbus_read(DEVICE(s)->canonical_path, offset, value, size);
+
+    return value;
+}
+
+static void npcm7xx_smbus_write(void *opaque, hwaddr offset, uint64_t value,
+                              unsigned size)
+{
+    NPCM7xxSMBusState *s = opaque;
+    uint8_t bank = s->ctl3 & NPCM7XX_SMBCTL3_BNK_SEL;
+
+    trace_npcm7xx_smbus_write(DEVICE(s)->canonical_path, offset, value, size);
+
+    /* The order of the registers are their order in memory. */
+    switch (offset) {
+    case NPCM7XX_SMB_SDA:
+        npcm7xx_smbus_write_sda(s, value);
+        break;
+
+    case NPCM7XX_SMB_ST:
+        npcm7xx_smbus_write_st(s, value);
+        break;
+
+    case NPCM7XX_SMB_CST:
+        npcm7xx_smbus_write_cst(s, value);
+        break;
+
+    case NPCM7XX_SMB_CTL1:
+        npcm7xx_smbus_write_ctl1(s, value);
+        break;
+
+    case NPCM7XX_SMB_ADDR1:
+        s->addr[0] = value;
+        break;
+
+    case NPCM7XX_SMB_CTL2:
+        npcm7xx_smbus_write_ctl2(s, value);
+        break;
+
+    case NPCM7XX_SMB_ADDR2:
+        s->addr[1] = value;
+        break;
+
+    case NPCM7XX_SMB_CTL3:
+        npcm7xx_smbus_write_ctl3(s, value);
+        break;
+
+    case NPCM7XX_SMB_CST2:
+        qemu_log_mask(LOG_GUEST_ERROR,
+                "%s: write to read-only reg: offset 0x%" HWADDR_PRIx "\n",
+                DEVICE(s)->canonical_path, offset);
+        break;
+
+    case NPCM7XX_SMB_CST3:
+        npcm7xx_smbus_write_cst3(s, value);
+        break;
+
+    case NPCM7XX_SMB_VER:
+        qemu_log_mask(LOG_GUEST_ERROR,
+                "%s: write to read-only reg: offset 0x%" HWADDR_PRIx "\n",
+                DEVICE(s)->canonical_path, offset);
+        break;
+
+    /* This register is either invalid or banked at this point. */
+    default:
+        if (bank) {
+            /* Bank 1 */
+            qemu_log_mask(LOG_GUEST_ERROR,
+                    "%s: write to invalid offset 0x%" HWADDR_PRIx "\n",
+                    DEVICE(s)->canonical_path, offset);
+        } else {
+            /* Bank 0 */
+            switch (offset) {
+            case NPCM7XX_SMB_ADDR3:
+                s->addr[2] = value;
+                break;
+
+            case NPCM7XX_SMB_ADDR7:
+                s->addr[6] = value;
+                break;
+
+            case NPCM7XX_SMB_ADDR4:
+                s->addr[3] = value;
+                break;
+
+            case NPCM7XX_SMB_ADDR8:
+                s->addr[7] = value;
+                break;
+
+            case NPCM7XX_SMB_ADDR5:
+                s->addr[4] = value;
+                break;
+
+            case NPCM7XX_SMB_ADDR9:
+                s->addr[8] = value;
+                break;
+
+            case NPCM7XX_SMB_ADDR6:
+                s->addr[5] = value;
+                break;
+
+            case NPCM7XX_SMB_ADDR10:
+                s->addr[9] = value;
+                break;
+
+            case NPCM7XX_SMB_CTL4:
+                s->ctl4 = value;
+                break;
+
+            case NPCM7XX_SMB_CTL5:
+                s->ctl5 = value;
+                break;
+
+            case NPCM7XX_SMB_SCLLT:
+                s->scllt = value;
+                break;
+
+            case NPCM7XX_SMB_SCLHT:
+                s->sclht = value;
+                break;
+
+            default:
+                qemu_log_mask(LOG_GUEST_ERROR,
+                        "%s: write to invalid offset 0x%" HWADDR_PRIx "\n",
+                        DEVICE(s)->canonical_path, offset);
+                break;
+            }
+        }
+        break;
+    }
+}
+
+static const MemoryRegionOps npcm7xx_smbus_ops = {
+    .read = npcm7xx_smbus_read,
+    .write = npcm7xx_smbus_write,
+    .endianness = DEVICE_LITTLE_ENDIAN,
+    .valid = {
+        .min_access_size = 1,
+        .max_access_size = 1,
+        .unaligned = false,
+    },
+};
+
+static void npcm7xx_smbus_enter_reset(Object *obj, ResetType type)
+{
+    NPCM7xxSMBusState *s = NPCM7XX_SMBUS(obj);
+
+    s->st = NPCM7XX_SMB_ST_INIT_VAL;
+    s->cst = NPCM7XX_SMB_CST_INIT_VAL;
+    s->cst2 = NPCM7XX_SMB_CST2_INIT_VAL;
+    s->cst3 = NPCM7XX_SMB_CST3_INIT_VAL;
+    s->ctl1 = NPCM7XX_SMB_CTL1_INIT_VAL;
+    s->ctl2 = NPCM7XX_SMB_CTL2_INIT_VAL;
+    s->ctl3 = NPCM7XX_SMB_CTL3_INIT_VAL;
+    s->ctl4 = NPCM7XX_SMB_CTL4_INIT_VAL;
+    s->ctl5 = NPCM7XX_SMB_CTL5_INIT_VAL;
+
+    for (int i = 0; i < NPCM7XX_SMBUS_NR_ADDRS; ++i) {
+        s->addr[i] = NPCM7XX_SMB_ADDR_INIT_VAL;
+    }
+    s->scllt = NPCM7XX_SMB_SCLLT_INIT_VAL;
+    s->sclht = NPCM7XX_SMB_SCLHT_INIT_VAL;
+
+    s->status = NPCM7XX_SMBUS_STATUS_IDLE;
+}
+
+static void npcm7xx_smbus_hold_reset(Object *obj)
+{
+    NPCM7xxSMBusState *s = NPCM7XX_SMBUS(obj);
+
+    qemu_irq_lower(s->irq);
+}
+
+static void npcm7xx_smbus_init(Object *obj)
+{
+    NPCM7xxSMBusState *s = NPCM7XX_SMBUS(obj);
+    SysBusDevice *sbd = SYS_BUS_DEVICE(obj);
+
+    sysbus_init_irq(sbd, &s->irq);
+    memory_region_init_io(&s->iomem, obj, &npcm7xx_smbus_ops, s,
+                          "regs", 4 * KiB);
+    sysbus_init_mmio(sbd, &s->iomem);
+
+    s->bus = i2c_init_bus(DEVICE(s), "i2c-bus");
+    s->status = NPCM7XX_SMBUS_STATUS_IDLE;
+}
+
+static const VMStateDescription vmstate_npcm7xx_smbus = {
+    .name = "npcm7xx-smbus",
+    .version_id = 0,
+    .minimum_version_id = 0,
+    .fields = (VMStateField[]) {
+        VMSTATE_UINT8(sda, NPCM7xxSMBusState),
+        VMSTATE_UINT8(st, NPCM7xxSMBusState),
+        VMSTATE_UINT8(cst, NPCM7xxSMBusState),
+        VMSTATE_UINT8(cst2, NPCM7xxSMBusState),
+        VMSTATE_UINT8(cst3, NPCM7xxSMBusState),
+        VMSTATE_UINT8(ctl1, NPCM7xxSMBusState),
+        VMSTATE_UINT8(ctl2, NPCM7xxSMBusState),
+        VMSTATE_UINT8(ctl3, NPCM7xxSMBusState),
+        VMSTATE_UINT8(ctl4, NPCM7xxSMBusState),
+        VMSTATE_UINT8(ctl5, NPCM7xxSMBusState),
+        VMSTATE_UINT8_ARRAY(addr, NPCM7xxSMBusState, NPCM7XX_SMBUS_NR_ADDRS),
+        VMSTATE_UINT8(scllt, NPCM7xxSMBusState),
+        VMSTATE_UINT8(sclht, NPCM7xxSMBusState),
+        VMSTATE_END_OF_LIST(),
+    },
+};
+
+static void npcm7xx_smbus_class_init(ObjectClass *klass, void *data)
+{
+    ResettableClass *rc = RESETTABLE_CLASS(klass);
+    DeviceClass *dc = DEVICE_CLASS(klass);
+
+    dc->desc = "NPCM7xx System Management Bus";
+    dc->vmsd = &vmstate_npcm7xx_smbus;
+    rc->phases.enter = npcm7xx_smbus_enter_reset;
+    rc->phases.hold = npcm7xx_smbus_hold_reset;
+}
+
+static const TypeInfo npcm7xx_smbus_types[] = {
+    {
+        .name = TYPE_NPCM7XX_SMBUS,
+        .parent = TYPE_SYS_BUS_DEVICE,
+        .instance_size = sizeof(NPCM7xxSMBusState),
+        .class_init = npcm7xx_smbus_class_init,
+        .instance_init = npcm7xx_smbus_init,
+    },
+};
+DEFINE_TYPES(npcm7xx_smbus_types);