drivers/smbus: initialize SC16IS7XX I2C to UART converter chip

This patch adds the functionality to initialize the sc16is750
i2c to uart converter chip with a 14.7MHz input clock to support
115200 baud rate.

Change-Id: Ib31188b8c0f9b0ce9454da984e630eca9101d145
Signed-off-by: Husni Faiz <ahamedhusni73@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/67342
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Tim Wawrzynczak <inforichland@gmail.com>
Reviewed-by: Raul Rangel <rrangel@chromium.org>

src/drivers/smbus/Makefile.inc

@@ -1,3 +1,8 @@
+ifeq ($(CONFIG_SC16IS7XX_INIT),y)
+bootblock-y += sc16is7xx_init.c
+romstage-y += sc16is7xx_init.c
+endif
+
 ifeq ($(CONFIG_CONSOLE_I2C_SMBUS),y)
 all-y += i2c_smbus_console.c
 endif

src/drivers/smbus/i2c_smbus_console.c

@@ -3,8 +3,13 @@
 #include <console/i2c_smbus.h>
 #include <device/smbus_host.h>
 #include <southbridge/intel/bd82x6x/pch.h>
+#include "sc16is7xx_init.h"
 
-void i2c_smbus_console_init(void) {}
+void i2c_smbus_console_init(void)
+{
+	if (CONFIG(SC16IS7XX_INIT))
+		sc16is7xx_init();
+}
 
 void i2c_smbus_console_tx_byte(unsigned char c)
 {

src/drivers/smbus/sc16is7xx_init.c

@@ -0,0 +1,62 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+
+#include <console/i2c_smbus.h>
+#include <device/i2c.h>
+#include <device/smbus_host.h>
+#include <southbridge/intel/bd82x6x/pch.h>
+#include "sc16is7xx_init.h"
+
+/*
+ * Datasheet - SC16IS740/750/760, Rev. 7 - 9 June 2011
+ * https://web.archive.org/web/20210612105830/https://www.nxp.com/docs/en/data-sheet/SC16IS740_750_760.pdf
+ */
+
+// Bits [6:3] of the subaddress is to address device internal registers
+#define INTERNAL_REG_SUB_ADDR_SHIFT	3
+
+#define REG_THR 0x00    // Transmit Holding Register
+#define REG_LCR 0x03    // Line Control Register
+
+// Special Register Set is accessible only when LCR[7] is logic 1
+#define REG_DLL 0x00    // divisor latch LSB
+#define REG_DLH 0x01    // divisor latch MSB
+
+#define LCR_WORD_LEN_BIT_0	BIT(0)
+#define LCR_WORD_LEN_BIT_1	BIT(1)
+#define LCR_STOP_BIT		BIT(2)
+#define LCR_PARITY_BIT_0	BIT(3)
+#define LCR_PARITY_BIT_1	BIT(4)
+#define LCR_PARITY_BIT_2	BIT(5)
+#define LCR_BREAK_CTL_BIT	BIT(6)
+#define LCR_SPEC_REG_SET_EN	BIT(7)
+
+#define UART_8_N_1	(LCR_WORD_LEN_BIT_0 | LCR_WORD_LEN_BIT_1)
+
+/*
+ *	UART configuration: 8 bit word length, No parity, 1 stop bit (8-N-1)
+ *	Divisor value set here is calculated for 115200 baud rate
+ *	in 14.7MHz clock input to chip.
+ */
+
+#define BAUD_115200_DLL	0x08
+#define BAUD_115200_DLH	0x00
+
+void sc16is7xx_write_byte(uint8_t reg, unsigned char c)
+{
+	do_smbus_write_byte(CONFIG_FIXED_SMBUS_IO_BASE,
+			CONFIG_CONSOLE_I2C_SMBUS_SLAVE_ADDRESS, reg, c);
+}
+
+void sc16is7xx_init(void)
+{
+	// Configure 8-N-1 and enable special register set
+	sc16is7xx_write_byte(REG_LCR << INTERNAL_REG_SUB_ADDR_SHIFT,
+				(UART_8_N_1 | LCR_SPEC_REG_SET_EN));
+
+	sc16is7xx_write_byte(REG_DLL << INTERNAL_REG_SUB_ADDR_SHIFT, BAUD_115200_DLL);
+	sc16is7xx_write_byte(REG_DLH << INTERNAL_REG_SUB_ADDR_SHIFT, BAUD_115200_DLH);
+
+	// Disable special register set
+	sc16is7xx_write_byte(REG_LCR << INTERNAL_REG_SUB_ADDR_SHIFT,
+				(UART_8_N_1 & ~LCR_SPEC_REG_SET_EN));
+}

src/drivers/smbus/sc16is7xx_init.h

@@ -0,0 +1,11 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+
+#ifndef __DRIVERS_SMBUS_SC16IS7XX_INIT__
+#define __DRIVERS_SMBUS_SC16IS7XX_INIT__
+
+#include <types.h>
+
+void sc16is7xx_write_byte(uint8_t reg, unsigned char c);
+void sc16is7xx_init(void);
+
+#endif /* __DRIVERS_SMBUS_SC16IS7XX_INIT__ */