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From:   Tali Perry <tali.perry1@gmail.com>
To:     ofery@google.com, brendanhiggins@google.com,
        avifishman70@gmail.com, tmaimon77@gmail.com, kfting@nuvoton.com,
        venture@google.com, yuenn@google.com, benjaminfair@google.com,
        robh+dt@kernel.org, wsa@the-dreams.de,
        andriy.shevchenko@linux.intel.com
Cc:     linux-arm-kernel@lists.infradead.org, linux-i2c@vger.kernel.org,
        openbmc@lists.ozlabs.org, devicetree@vger.kernel.org,
        linux-kernel@vger.kernel.org, Tali Perry <tali.perry1@gmail.com>
Subject: [PATCH v13 3/3] i2c: npcm7xx: Add support for slave mode for Nuvoton
Date:   Fri, 22 May 2020 14:33:12 +0300
Message-Id: <20200522113312.181413-4-tali.perry1@gmail.com>
In-Reply-To: <20200522113312.181413-1-tali.perry1@gmail.com>
References: <20200522113312.181413-1-tali.perry1@gmail.com>
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Sender: linux-kernel-owner@vger.kernel.org
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Add support for slave mode for Nuvoton
NPCM BMC I2C controller driver.

Signed-off-by: Tali Perry <tali.perry1@gmail.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
---
 drivers/i2c/busses/i2c-npcm7xx.c | 609 ++++++++++++++++++++++++++++++-
 1 file changed, 608 insertions(+), 1 deletion(-)

diff --git a/drivers/i2c/busses/i2c-npcm7xx.c b/drivers/i2c/busses/i2c-npcm7xx.c
index c6e512908fa2..579985f0a6f2 100644
--- a/drivers/i2c/busses/i2c-npcm7xx.c
+++ b/drivers/i2c/busses/i2c-npcm7xx.c
@@ -71,6 +71,24 @@ enum i2c_state {
 	I2C_STOP_PENDING,
 };
 
+#if IS_ENABLED(CONFIG_I2C_SLAVE)
+/* Module supports setting multiple own slave addresses */
+enum i2c_addr {
+	I2C_SLAVE_ADDR1 = 0,
+	I2C_SLAVE_ADDR2,
+	I2C_SLAVE_ADDR3,
+	I2C_SLAVE_ADDR4,
+	I2C_SLAVE_ADDR5,
+	I2C_SLAVE_ADDR6,
+	I2C_SLAVE_ADDR7,
+	I2C_SLAVE_ADDR8,
+	I2C_SLAVE_ADDR9,
+	I2C_SLAVE_ADDR10,
+	I2C_GC_ADDR,
+	I2C_ARP_ADDR,
+};
+#endif
+
 /* init register and default value required to enable module */
 #define NPCM_I2CSEGCTL			0xE4
 #define NPCM_I2CSEGCTL_INIT_VAL		0x0333F000
@@ -98,6 +116,23 @@ enum i2c_state {
 #define NPCM_I2CADDR6			0x16
 #define NPCM_I2CADDR10			0x17
 
+#if IS_ENABLED(CONFIG_I2C_SLAVE)
+/*
+ * npcm_i2caddr array:
+ * The module supports having multiple own slave addresses.
+ * Since the addr regs are sprinkled all over the address space,
+ * use this array to get the address or each register.
+ */
+#define I2C_NUM_OWN_ADDR 10
+const int npcm_i2caddr[I2C_NUM_OWN_ADDR] = {
+					    NPCM_I2CADDR1, NPCM_I2CADDR2,
+					    NPCM_I2CADDR3, NPCM_I2CADDR4,
+					    NPCM_I2CADDR5, NPCM_I2CADDR6,
+					    NPCM_I2CADDR7, NPCM_I2CADDR8,
+					    NPCM_I2CADDR9, NPCM_I2CADDR10,
+					   };
+#endif
+
 #define NPCM_I2CCTL4			0x1A
 #define NPCM_I2CCTL5			0x1B
 #define NPCM_I2CSCLLT			0x1C /* SCL Low Time */
@@ -269,6 +304,16 @@ struct npcm_i2c {
 	unsigned long int_time_stamp;
 	unsigned long bus_freq; /* in kHz */
 	u32 xmits;
+#if IS_ENABLED(CONFIG_I2C_SLAVE)
+	u8 own_slave_addr;
+	struct i2c_client *slave;
+	int slv_rd_size;
+	int slv_rd_ind;
+	int slv_wr_size;
+	int slv_wr_ind;
+	u8 slv_rd_buf[I2C_HW_FIFO_SIZE];
+	u8 slv_wr_buf[I2C_HW_FIFO_SIZE];
+#endif
 	struct dentry *debugfs; /* debugfs device directory */
 	u64 ber_cnt;
 	u64 rec_succ_cnt;
@@ -301,6 +346,10 @@ static void npcm_i2c_init_params(struct npcm_i2c *bus)
 	bus->int_time_stamp = 0;
 	bus->PEC_use = false;
 	bus->PEC_mask = 0;
+#if IS_ENABLED(CONFIG_I2C_SLAVE)
+	if (bus->slave)
+		bus->master_or_slave = I2C_SLAVE;
+#endif
 }
 
 static inline void npcm_i2c_wr_byte(struct npcm_i2c *bus, u8 data)
@@ -346,6 +395,18 @@ static void npcm_i2c_disable(struct npcm_i2c *bus)
 {
 	u8 i2cctl2;
 
+#if IS_ENABLED(CONFIG_I2C_SLAVE)
+	int i;
+
+	/* select bank 0 for I2C addresses */
+	npcm_i2c_select_bank(bus, I2C_BANK_0);
+
+	/* Slave addresses removal */
+	for (i = I2C_SLAVE_ADDR1; i < I2C_NUM_OWN_ADDR; i++)
+		iowrite8(0, bus->reg + npcm_i2caddr[i]);
+
+	npcm_i2c_select_bank(bus, I2C_BANK_1);
+#endif
 	/* Disable module */
 	i2cctl2 = ioread8(bus->reg + NPCM_I2CCTL2);
 	i2cctl2 = i2cctl2 & ~I2CCTL2_ENABLE;
@@ -509,6 +570,61 @@ static inline void npcm_i2c_nack(struct npcm_i2c *bus)
 	iowrite8(val, bus->reg + NPCM_I2CCTL1);
 }
 
+#if IS_ENABLED(CONFIG_I2C_SLAVE)
+static void npcm_i2c_slave_int_enable(struct npcm_i2c *bus, bool enable)
+{
+	u8 i2cctl1;
+
+	/* enable interrupt on slave match: */
+	i2cctl1 = ioread8(bus->reg + NPCM_I2CCTL1);
+	i2cctl1 &= ~NPCM_I2CCTL1_RWS;
+	if (enable)
+		i2cctl1 |= NPCM_I2CCTL1_NMINTE;
+	else
+		i2cctl1 &= ~NPCM_I2CCTL1_NMINTE;
+	iowrite8(i2cctl1, bus->reg + NPCM_I2CCTL1);
+}
+
+static int npcm_i2c_slave_enable(struct npcm_i2c *bus, enum i2c_addr addr_type,
+				  u8 addr, bool enable)
+{
+	u8 i2cctl1;
+	u8 i2cctl3;
+	u8 sa_reg;
+
+	sa_reg = (addr & 0x7F) | FIELD_PREP(NPCM_I2CADDR_SAEN, enable);
+	if (addr_type == I2C_GC_ADDR) {
+		i2cctl1 = ioread8(bus->reg + NPCM_I2CCTL1);
+		if (enable)
+			i2cctl1 |= NPCM_I2CCTL1_GCMEN;
+		else
+			i2cctl1 &= ~NPCM_I2CCTL1_GCMEN;
+		iowrite8(i2cctl1, bus->reg + NPCM_I2CCTL1);
+		return 0;
+	}
+	if (addr_type == I2C_ARP_ADDR) {
+		i2cctl3 = ioread8(bus->reg + NPCM_I2CCTL3);
+		if (enable)
+			i2cctl3 |= I2CCTL3_ARPMEN;
+		else
+			i2cctl3 &= ~I2CCTL3_ARPMEN;
+		iowrite8(i2cctl3, bus->reg + NPCM_I2CCTL3);
+		return 0;
+	}
+	if (addr_type >= I2C_ARP_ADDR)
+		return -EFAULT;
+	/* select bank 0 for address 3 to 10 */
+	if (addr_type > I2C_SLAVE_ADDR2)
+		npcm_i2c_select_bank(bus, I2C_BANK_0);
+	/* Set and enable the address */
+	iowrite8(sa_reg, bus->reg + npcm_i2caddr[(int)addr_type]);
+	npcm_i2c_slave_int_enable(bus, enable);
+	if (addr_type > I2C_SLAVE_ADDR2)
+		npcm_i2c_select_bank(bus, I2C_BANK_1);
+	return 0;
+}
+#endif
+
 static void npcm_i2c_reset(struct npcm_i2c *bus)
 {
 	/*
@@ -517,6 +633,7 @@ static void npcm_i2c_reset(struct npcm_i2c *bus)
 	 */
 	u8 i2cctl1;
 	u8 i2cctl2;
+	u8 addr;
 
 	i2cctl1 = ioread8(bus->reg + NPCM_I2CCTL1);
 	i2cctl2 = ioread8(bus->reg + NPCM_I2CCTL2);
@@ -538,6 +655,13 @@ static void npcm_i2c_reset(struct npcm_i2c *bus)
 	/* Clear all fifo bits: */
 	iowrite8(NPCM_I2CFIF_CTS_CLR_FIFO, bus->reg + NPCM_I2CFIF_CTS);
 
+#if IS_ENABLED(CONFIG_I2C_SLAVE)
+	if (bus->slave) {
+		addr = bus->slave->addr;
+		npcm_i2c_slave_enable(bus, I2C_SLAVE_ADDR1, addr, true);
+	}
+#endif
+
 	bus->state = I2C_IDLE;
 }
 
@@ -603,6 +727,10 @@ static void npcm_i2c_callback(struct npcm_i2c *bus,
 	}
 
 	bus->operation = I2C_NO_OPER;
+#if IS_ENABLED(CONFIG_I2C_SLAVE)
+	if (bus->slave)
+		bus->master_or_slave = I2C_SLAVE;
+#endif
 }
 
 static u8 npcm_i2c_fifo_usage(struct npcm_i2c *bus)
@@ -714,6 +842,460 @@ static void npcm_i2c_master_abort(struct npcm_i2c *bus)
 	npcm_i2c_clear_master_status(bus);
 }
 
+#if IS_ENABLED(CONFIG_I2C_SLAVE)
+static u8 npcm_i2c_get_slave_addr(struct npcm_i2c *bus, enum i2c_addr addr_type)
+{
+	u8 slave_add;
+
+	/* select bank 0 for address 3 to 10 */
+	if (addr_type > I2C_SLAVE_ADDR2)
+		npcm_i2c_select_bank(bus, I2C_BANK_0);
+
+	slave_add = ioread8(bus->reg + npcm_i2caddr[(int)addr_type]);
+
+	if (addr_type > I2C_SLAVE_ADDR2)
+		npcm_i2c_select_bank(bus, I2C_BANK_1);
+
+	return slave_add;
+}
+
+static int npcm_i2c_remove_slave_addr(struct npcm_i2c *bus, u8 slave_add)
+{
+	int i;
+
+	/* Set the enable bit */
+	slave_add |= 0x80;
+	npcm_i2c_select_bank(bus, I2C_BANK_0);
+	for (i = I2C_SLAVE_ADDR1; i < I2C_NUM_OWN_ADDR; i++) {
+		if (ioread8(bus->reg + npcm_i2caddr[i]) == slave_add)
+			iowrite8(0, bus->reg + npcm_i2caddr[i]);
+	}
+	npcm_i2c_select_bank(bus, I2C_BANK_1);
+	return 0;
+}
+
+static void npcm_i2c_write_fifo_slave(struct npcm_i2c *bus, u16 max_bytes)
+{
+	/*
+	 * Fill the FIFO, while the FIFO is not full and there are more bytes
+	 * to write
+	 */
+	npcm_i2c_clear_fifo_int(bus);
+	npcm_i2c_clear_tx_fifo(bus);
+	iowrite8(0, bus->reg + NPCM_I2CTXF_CTL);
+	while (max_bytes-- && I2C_HW_FIFO_SIZE != npcm_i2c_fifo_usage(bus)) {
+		if (bus->slv_wr_size <= 0)
+			break;
+		bus->slv_wr_ind = bus->slv_wr_ind % I2C_HW_FIFO_SIZE;
+		npcm_i2c_wr_byte(bus, bus->slv_wr_buf[bus->slv_wr_ind]);
+		bus->slv_wr_ind++;
+		bus->slv_wr_ind = bus->slv_wr_ind % I2C_HW_FIFO_SIZE;
+		bus->slv_wr_size--;
+	}
+}
+
+static void npcm_i2c_read_fifo_slave(struct npcm_i2c *bus, u8 bytes_in_fifo)
+{
+	u8 data;
+
+	if (!bus->slave)
+		return;
+
+	while (bytes_in_fifo--) {
+		data = npcm_i2c_rd_byte(bus);
+
+		bus->slv_rd_ind = bus->slv_rd_ind % I2C_HW_FIFO_SIZE;
+		bus->slv_rd_buf[bus->slv_rd_ind] = data;
+		bus->slv_rd_ind++;
+
+		/* 1st byte is length in block protocol: */
+		if (bus->slv_rd_ind == 1 && bus->read_block_use)
+			bus->slv_rd_size = data + bus->PEC_use + 1;
+	}
+}
+
+static int npcm_i2c_slave_get_wr_buf(struct npcm_i2c *bus)
+{
+	int i;
+	u8 value;
+	int ind;
+	int ret = bus->slv_wr_ind;
+
+	/* fill a cyclic buffer */
+	for (i = 0; i < I2C_HW_FIFO_SIZE; i++) {
+		if (bus->slv_wr_size >= I2C_HW_FIFO_SIZE)
+			break;
+		i2c_slave_event(bus->slave, I2C_SLAVE_READ_REQUESTED, &value);
+		ind = (bus->slv_wr_ind + bus->slv_wr_size) % I2C_HW_FIFO_SIZE;
+		bus->slv_wr_buf[ind] = value;
+		bus->slv_wr_size++;
+		i2c_slave_event(bus->slave, I2C_SLAVE_READ_PROCESSED, &value);
+	}
+	return I2C_HW_FIFO_SIZE - ret;
+}
+
+static void npcm_i2c_slave_send_rd_buf(struct npcm_i2c *bus)
+{
+	int i;
+
+	for (i = 0; i < bus->slv_rd_ind; i++)
+		i2c_slave_event(bus->slave, I2C_SLAVE_WRITE_RECEIVED,
+				&bus->slv_rd_buf[i]);
+	/*
+	 * once we send bytes up, need to reset the counter of the wr buf
+	 * got data from master (new offset in device), ignore wr fifo:
+	 */
+	if (bus->slv_rd_ind) {
+		bus->slv_wr_size = 0;
+		bus->slv_wr_ind = 0;
+	}
+
+	bus->slv_rd_ind = 0;
+	bus->slv_rd_size = bus->adap.quirks->max_read_len;
+
+	npcm_i2c_clear_fifo_int(bus);
+	npcm_i2c_clear_rx_fifo(bus);
+}
+
+static void npcm_i2c_slave_receive(struct npcm_i2c *bus, u16 nread,
+				   u8 *read_data)
+{
+	bus->state = I2C_OPER_STARTED;
+	bus->operation = I2C_READ_OPER;
+	bus->slv_rd_size = nread;
+	bus->slv_rd_ind = 0;
+
+	iowrite8(0, bus->reg + NPCM_I2CTXF_CTL);
+	iowrite8(I2C_HW_FIFO_SIZE, bus->reg + NPCM_I2CRXF_CTL);
+	npcm_i2c_clear_tx_fifo(bus);
+	npcm_i2c_clear_rx_fifo(bus);
+}
+
+static void npcm_i2c_slave_xmit(struct npcm_i2c *bus, u16 nwrite,
+				u8 *write_data)
+{
+	if (nwrite == 0)
+		return;
+
+	bus->state = I2C_OPER_STARTED;
+	bus->operation = I2C_WRITE_OPER;
+
+	/* get the next buffer */
+	npcm_i2c_slave_get_wr_buf(bus);
+	npcm_i2c_write_fifo_slave(bus, nwrite);
+}
+
+/*
+ * npcm_i2c_slave_wr_buf_sync:
+ * currently slave IF only supports single byte operations.
+ * in order to utilyze the npcm HW FIFO, the driver will ask for 16 bytes
+ * at a time, pack them in buffer, and then transmit them all together
+ * to the FIFO and onward to the bus.
+ * NACK on read will be once reached to bus->adap->quirks->max_read_len.
+ * sending a NACK wherever the backend requests for it is not supported.
+ * the next two functions allow reading to local buffer before writing it all
+ * to the HW FIFO.
+ */
+static void npcm_i2c_slave_wr_buf_sync(struct npcm_i2c *bus)
+{
+	int left_in_fifo;
+
+	left_in_fifo = FIELD_GET(NPCM_I2CTXF_STS_TX_BYTES,
+				 ioread8(bus->reg + NPCM_I2CTXF_STS));
+
+	/* fifo already full: */
+	if (left_in_fifo >= I2C_HW_FIFO_SIZE ||
+	    bus->slv_wr_size >= I2C_HW_FIFO_SIZE)
+		return;
+
+	/* update the wr fifo index back to the untransmitted bytes: */
+	bus->slv_wr_ind = bus->slv_wr_ind - left_in_fifo;
+	bus->slv_wr_size = bus->slv_wr_size + left_in_fifo;
+
+	if (bus->slv_wr_ind < 0)
+		bus->slv_wr_ind += I2C_HW_FIFO_SIZE;
+}
+
+static void npcm_i2c_slave_rd_wr(struct npcm_i2c *bus)
+{
+	if (NPCM_I2CST_XMIT & ioread8(bus->reg + NPCM_I2CST)) {
+		/*
+		 * Slave got an address match with direction bit 1 so it should
+		 * transmit data. Write till the master will NACK
+		 */
+		bus->operation = I2C_WRITE_OPER;
+		npcm_i2c_slave_xmit(bus, bus->adap.quirks->max_write_len,
+				    bus->slv_wr_buf);
+	} else {
+		/*
+		 * Slave got an address match with direction bit 0 so it should
+		 * receive data.
+		 * this module does not support saying no to bytes.
+		 * it will always ACK.
+		 */
+		bus->operation = I2C_READ_OPER;
+		npcm_i2c_read_fifo_slave(bus, npcm_i2c_fifo_usage(bus));
+		bus->stop_ind = I2C_SLAVE_RCV_IND;
+		npcm_i2c_slave_send_rd_buf(bus);
+		npcm_i2c_slave_receive(bus, bus->adap.quirks->max_read_len,
+				       bus->slv_rd_buf);
+	}
+}
+
+static irqreturn_t npcm_i2c_int_slave_handler(struct npcm_i2c *bus)
+{
+	u8 val;
+	irqreturn_t ret = IRQ_NONE;
+	u8 i2cst = ioread8(bus->reg + NPCM_I2CST);
+
+	/* Slave: A NACK has occurred */
+	if (NPCM_I2CST_NEGACK & i2cst) {
+		bus->stop_ind = I2C_NACK_IND;
+		npcm_i2c_slave_wr_buf_sync(bus);
+		if (bus->fifo_use)
+			/* clear the FIFO */
+			iowrite8(NPCM_I2CFIF_CTS_CLR_FIFO,
+				 bus->reg + NPCM_I2CFIF_CTS);
+
+		/* In slave write, NACK is OK, otherwise it is a problem */
+		bus->stop_ind = I2C_NO_STATUS_IND;
+		bus->operation = I2C_NO_OPER;
+		bus->own_slave_addr = 0xFF;
+
+		/*
+		 * Slave has to wait for STOP to decide this is the end
+		 * of the transaction. tx is not yet considered as done
+		 */
+		iowrite8(NPCM_I2CST_NEGACK, bus->reg + NPCM_I2CST);
+
+		ret = IRQ_HANDLED;
+	}
+
+	/* Slave mode: a Bus Error (BER) has been identified */
+	if (NPCM_I2CST_BER & i2cst) {
+		/*
+		 * Check whether bus arbitration or Start or Stop during data
+		 * xfer bus arbitration problem should not result in recovery
+		 */
+		bus->stop_ind = I2C_BUS_ERR_IND;
+
+		/* wait for bus busy before clear fifo */
+		iowrite8(NPCM_I2CFIF_CTS_CLR_FIFO, bus->reg + NPCM_I2CFIF_CTS);
+
+		bus->state = I2C_IDLE;
+
+		/*
+		 * in BER case we might get 2 interrupts: one for slave one for
+		 * master ( for a channel which is master\slave switching)
+		 */
+		if (completion_done(&bus->cmd_complete) == false) {
+			bus->cmd_err = -EIO;
+			complete(&bus->cmd_complete);
+		}
+		bus->own_slave_addr = 0xFF;
+		iowrite8(NPCM_I2CST_BER, bus->reg + NPCM_I2CST);
+		ret = IRQ_HANDLED;
+	}
+
+	/* A Slave Stop Condition has been identified */
+	if (NPCM_I2CST_SLVSTP & i2cst) {
+		u8 bytes_in_fifo = npcm_i2c_fifo_usage(bus);
+
+		bus->stop_ind = I2C_SLAVE_DONE_IND;
+
+		if (bus->operation == I2C_READ_OPER)
+			npcm_i2c_read_fifo_slave(bus, bytes_in_fifo);
+
+		/* if the buffer is empty nothing will be sent */
+		npcm_i2c_slave_send_rd_buf(bus);
+
+		/* Slave done transmitting or receiving */
+		bus->stop_ind = I2C_NO_STATUS_IND;
+
+		/*
+		 * Note, just because we got here, it doesn't mean we through
+		 * away the wr buffer.
+		 * we keep it until the next received offset.
+		 */
+		bus->operation = I2C_NO_OPER;
+		bus->int_cnt = 0;
+		bus->own_slave_addr = 0xFF;
+		i2c_slave_event(bus->slave, I2C_SLAVE_STOP, 0);
+		iowrite8(NPCM_I2CST_SLVSTP, bus->reg + NPCM_I2CST);
+		if (bus->fifo_use) {
+			npcm_i2c_clear_fifo_int(bus);
+			npcm_i2c_clear_rx_fifo(bus);
+			npcm_i2c_clear_tx_fifo(bus);
+
+			iowrite8(NPCM_I2CFIF_CTS_CLR_FIFO,
+				 bus->reg + NPCM_I2CFIF_CTS);
+		}
+		bus->state = I2C_IDLE;
+		ret = IRQ_HANDLED;
+	}
+
+	/* restart condition occurred and Rx-FIFO was not empty */
+	if (bus->fifo_use && FIELD_GET(NPCM_I2CFIF_CTS_SLVRSTR,
+				       ioread8(bus->reg + NPCM_I2CFIF_CTS))) {
+		bus->stop_ind = I2C_SLAVE_RESTART_IND;
+		bus->master_or_slave = I2C_SLAVE;
+		if (bus->operation == I2C_READ_OPER)
+			npcm_i2c_read_fifo_slave(bus, npcm_i2c_fifo_usage(bus));
+		bus->operation = I2C_WRITE_OPER;
+		iowrite8(0, bus->reg + NPCM_I2CRXF_CTL);
+		val = NPCM_I2CFIF_CTS_CLR_FIFO | NPCM_I2CFIF_CTS_SLVRSTR |
+		      NPCM_I2CFIF_CTS_RXF_TXE;
+		iowrite8(val, bus->reg + NPCM_I2CFIF_CTS);
+		npcm_i2c_slave_rd_wr(bus);
+		ret = IRQ_HANDLED;
+	}
+
+	/* A Slave Address Match has been identified */
+	if (NPCM_I2CST_NMATCH & i2cst) {
+		u8 info = 0;
+
+		/* Address match automatically implies slave mode */
+		bus->master_or_slave = I2C_SLAVE;
+		npcm_i2c_clear_fifo_int(bus);
+		npcm_i2c_clear_rx_fifo(bus);
+		npcm_i2c_clear_tx_fifo(bus);
+		iowrite8(0, bus->reg + NPCM_I2CTXF_CTL);
+		iowrite8(I2C_HW_FIFO_SIZE, bus->reg + NPCM_I2CRXF_CTL);
+		if (NPCM_I2CST_XMIT & i2cst) {
+			bus->operation = I2C_WRITE_OPER;
+		} else {
+			i2c_slave_event(bus->slave, I2C_SLAVE_WRITE_REQUESTED,
+					&info);
+			bus->operation = I2C_READ_OPER;
+		}
+		if (bus->own_slave_addr == 0xFF) {
+			/* Check which type of address match */
+			val = ioread8(bus->reg + NPCM_I2CCST);
+			if (NPCM_I2CCST_MATCH & val) {
+				u16 addr;
+				enum i2c_addr eaddr;
+				u8 i2ccst2;
+				u8 i2ccst3;
+
+				i2ccst3 = ioread8(bus->reg + NPCM_I2CCST3);
+				i2ccst2 = ioread8(bus->reg + NPCM_I2CCST2);
+
+				/*
+				 * the i2c module can response to 10 own SA.
+				 * check which one was addressed by the master.
+				 * repond to the first one.
+				 */
+				addr = ((i2ccst3 & 0x07) << 7) |
+					(i2ccst2 & 0x7F);
+				info = ffs(addr);
+				eaddr = (enum i2c_addr)info;
+				addr = npcm_i2c_get_slave_addr(bus, eaddr);
+				addr &= 0x7F;
+				bus->own_slave_addr = addr;
+				if (bus->PEC_mask & BIT(info))
+					bus->PEC_use = true;
+				else
+					bus->PEC_use = false;
+			} else {
+				if (NPCM_I2CCST_GCMATCH & val)
+					bus->own_slave_addr = 0;
+				if (NPCM_I2CCST_ARPMATCH & val)
+					bus->own_slave_addr = 0x61;
+			}
+		} else {
+			/*
+			 *  Slave match can happen in two options:
+			 *  1. Start, SA, read (slave read without further ado)
+			 *  2. Start, SA, read, data, restart, SA, read,  ...
+			 *     (slave read in fragmented mode)
+			 *  3. Start, SA, write, data, restart, SA, read, ..
+			 *     (regular write-read mode)
+			 */
+			if ((bus->state == I2C_OPER_STARTED &&
+			     bus->operation == I2C_READ_OPER &&
+			     bus->stop_ind == I2C_SLAVE_XMIT_IND) ||
+			     bus->stop_ind == I2C_SLAVE_RCV_IND) {
+				/* slave tx after slave rx w/o STOP */
+				bus->stop_ind = I2C_SLAVE_RESTART_IND;
+			}
+		}
+
+		if (NPCM_I2CST_XMIT & i2cst)
+			bus->stop_ind = I2C_SLAVE_XMIT_IND;
+		else
+			bus->stop_ind = I2C_SLAVE_RCV_IND;
+		bus->state = I2C_SLAVE_MATCH;
+		npcm_i2c_slave_rd_wr(bus);
+		iowrite8(NPCM_I2CST_NMATCH, bus->reg + NPCM_I2CST);
+		ret = IRQ_HANDLED;
+	}
+
+	/* Slave SDA status is set - tx or rx */
+	if ((NPCM_I2CST_SDAST & i2cst) ||
+	    (bus->fifo_use &&
+	    (npcm_i2c_tx_fifo_empty(bus) || npcm_i2c_rx_fifo_full(bus)))) {
+		npcm_i2c_slave_rd_wr(bus);
+		iowrite8(NPCM_I2CST_SDAST, bus->reg + NPCM_I2CST);
+		ret = IRQ_HANDLED;
+	} /* SDAST */
+
+	return ret;
+}
+
+static int npcm_i2c_reg_slave(struct i2c_client *client)
+{
+	unsigned long lock_flags;
+	struct npcm_i2c *bus = i2c_get_adapdata(client->adapter);
+
+	bus->slave = client;
+
+	if (!bus->slave)
+		return -EINVAL;
+
+	if (client->flags & I2C_CLIENT_TEN)
+		return -EAFNOSUPPORT;
+
+	spin_lock_irqsave(&bus->lock, lock_flags);
+
+	npcm_i2c_init_params(bus);
+	bus->slv_rd_size = 0;
+	bus->slv_wr_size = 0;
+	bus->slv_rd_ind = 0;
+	bus->slv_wr_ind = 0;
+	if (client->flags & I2C_CLIENT_PEC)
+		bus->PEC_use = true;
+
+	dev_info(bus->dev, "i2c%d register slave SA=0x%x, PEC=%d\n", bus->num,
+		 client->addr, bus->PEC_use);
+
+	npcm_i2c_slave_enable(bus, I2C_SLAVE_ADDR1, client->addr, true);
+	npcm_i2c_clear_fifo_int(bus);
+	npcm_i2c_clear_rx_fifo(bus);
+	npcm_i2c_clear_tx_fifo(bus);
+	npcm_i2c_slave_int_enable(bus, true);
+
+	spin_unlock_irqrestore(&bus->lock, lock_flags);
+	return 0;
+}
+
+static int npcm_i2c_unreg_slave(struct i2c_client *client)
+{
+	struct npcm_i2c *bus = client->adapter->algo_data;
+	unsigned long lock_flags;
+
+	spin_lock_irqsave(&bus->lock, lock_flags);
+	if (!bus->slave) {
+		spin_unlock_irqrestore(&bus->lock, lock_flags);
+		return -EINVAL;
+	}
+	npcm_i2c_slave_int_enable(bus, false);
+	npcm_i2c_remove_slave_addr(bus, client->addr);
+	bus->slave = NULL;
+	spin_unlock_irqrestore(&bus->lock, lock_flags);
+	return 0;
+}
+#endif /* CONFIG_I2C_SLAVE */
+
 static void npcm_i2c_master_fifo_read(struct npcm_i2c *bus)
 {
 	int rcount;
@@ -1399,6 +1981,9 @@ static int __npcm_i2c_init(struct npcm_i2c *bus, struct platform_device *pdev)
 	bus->master_or_slave = I2C_SLAVE;
 	bus->int_time_stamp = 0;
 	bus->xmits = 0;
+#if IS_ENABLED(CONFIG_I2C_SLAVE)
+	bus->slave = NULL;
+#endif
 
 	ret = device_property_read_u32(&pdev->dev, "bus-frequency",
 				       &clk_freq_hz);
@@ -1429,6 +2014,12 @@ static irqreturn_t npcm_i2c_bus_irq(int irq, void *dev_id)
 		if (!npcm_i2c_int_master_handler(bus))
 			return IRQ_HANDLED;
 	}
+#if IS_ENABLED(CONFIG_I2C_SLAVE)
+	if (bus->slave) {
+		bus->master_or_slave = I2C_SLAVE;
+		return npcm_i2c_int_slave_handler(bus);
+	}
+#endif
 	return IRQ_NONE;
 }
 
@@ -1570,6 +2161,11 @@ static int npcm_i2c_master_xfer(struct i2c_adapter *adap, struct i2c_msg *msgs,
 		 */
 		spin_lock_irqsave(&bus->lock, flags);
 		bus_busy = ioread8(bus->reg + NPCM_I2CCST) & NPCM_I2CCST_BB;
+#if IS_ENABLED(CONFIG_I2C_SLAVE)
+		if (!bus_busy && bus->slave)
+			iowrite8((bus->slave->addr & 0x7F),
+				 bus->reg + NPCM_I2CADDR1);
+#endif
 		spin_unlock_irqrestore(&bus->lock, flags);
 
 	} while (time_is_after_jiffies(time_left) && bus_busy);
@@ -1620,6 +2216,12 @@ static int npcm_i2c_master_xfer(struct i2c_adapter *adap, struct i2c_msg *msgs,
 	if (bus->cmd_err == -EAGAIN)
 		ret = i2c_recover_bus(adap);
 
+#if IS_ENABLED(CONFIG_I2C_SLAVE)
+	/* reenable slave if it was enabled */
+	if (bus->slave)
+		iowrite8((bus->slave->addr & 0x7F) | NPCM_I2CADDR_SAEN,
+			 bus->reg + NPCM_I2CADDR1);
+#endif
 	return bus->cmd_err;
 }
 
@@ -1628,7 +2230,8 @@ static u32 npcm_i2c_functionality(struct i2c_adapter *adap)
 	return I2C_FUNC_I2C |
 	       I2C_FUNC_SMBUS_EMUL |
 	       I2C_FUNC_SMBUS_BLOCK_DATA |
-	       I2C_FUNC_SMBUS_PEC;
+	       I2C_FUNC_SMBUS_PEC |
+	       I2C_FUNC_SLAVE;
 }
 
 static const struct i2c_adapter_quirks npcm_i2c_quirks = {
@@ -1641,6 +2244,10 @@ static const struct i2c_adapter_quirks npcm_i2c_quirks = {
 static const struct i2c_algorithm npcm_i2c_algo = {
 	.master_xfer = npcm_i2c_master_xfer,
 	.functionality = npcm_i2c_functionality,
+#if IS_ENABLED(CONFIG_I2C_SLAVE)
+	.reg_slave	= npcm_i2c_reg_slave,
+	.unreg_slave	= npcm_i2c_unreg_slave,
+#endif
 };
 
 /* i2c debugfs directory: used to keep health monitor of i2c devices */
-- 
2.22.0