[PATCH v2 2/7] serial: exar: add support for reading from Exar EEPROM

parker
2024-04-11T20:26:02Z

From: Parker Newman <pnewman@connecttech.com>

- Adds support for reading a word from the Exar EEPROM.
- Adds exar_write_reg/exar_read_reg for reading and writing to the UART's
config registers.

Signed-off-by: Parker Newman <pnewman@connecttech.com>
---
drivers/tty/serial/8250/8250_exar.c | 110 ++++++++++++++++++++++++++++
1 file changed, 110 insertions(+)

diff --git a/drivers/tty/serial/8250/8250_exar.c b/drivers/tty/serial/8250/8250_exar.c
index 4d1e07343d0b..49d690344e65 100644
--- a/drivers/tty/serial/8250/8250_exar.c
+++ b/drivers/tty/serial/8250/8250_exar.c
@@ -128,6 +128,16 @@
#define UART_EXAR_DLD 0x02 /* Divisor Fractional */
#define UART_EXAR_DLD_485_POLARITY 0x80 /* RS-485 Enable Signal Polarity */

+/* EEPROM registers */
+#define UART_EXAR_REGB 0x8e
+#define UART_EXAR_REGB_EECK BIT(4)
+#define UART_EXAR_REGB_EECS BIT(5)
+#define UART_EXAR_REGB_EEDI BIT(6)
+#define UART_EXAR_REGB_EEDO BIT(7)
+#define UART_EXAR_REGB_EE_ADDR_SIZE 6
+#define UART_EXAR_REGB_EE_DATA_SIZE 16
+
+
/*
* IOT2040 MPIO wiring semantics:
*
@@ -195,6 +205,106 @@ struct exar8250 {
int line[];
};

+static inline void exar_write_reg(struct exar8250 *priv,
+ unsigned int reg, uint8_t value)
+{
+ if (!priv || !priv->virt)
+ return;
+
+ writeb(value, priv->virt + reg);
+}
+
+static inline uint8_t exar_read_reg(struct exar8250 *priv, unsigned int reg)
+{
+ if (!priv || !priv->virt)
+ return 0;
+
+ return readb(priv->virt + reg);
+}
+
+static inline void exar_ee_select(struct exar8250 *priv, bool enable)
+{
+ uint8_t value = 0x00;
+
+ if (enable)
+ value |= UART_EXAR_REGB_EECS;
+
+ exar_write_reg(priv, UART_EXAR_REGB, value);
+ udelay(2);
+}
+
+static inline void exar_ee_write_bit(struct exar8250 *priv, int bit)
+{
+ uint8_t value = UART_EXAR_REGB_EECS;
+
+ if (bit)
+ value |= UART_EXAR_REGB_EEDI;
+
+ //Clock out the bit on the i2c interface
+ exar_write_reg(priv, UART_EXAR_REGB, value);
+ udelay(2);
+
+ value |= UART_EXAR_REGB_EECK;
+
+ exar_write_reg(priv, UART_EXAR_REGB, value);
+ udelay(2);
+}
+
+static inline uint8_t exar_ee_read_bit(struct exar8250 *priv)
+{
+ uint8_t regb;
+ uint8_t value = UART_EXAR_REGB_EECS;
+
+ //Clock in the bit on the i2c interface
+ exar_write_reg(priv, UART_EXAR_REGB, value);
+ udelay(2);
+
+ value |= UART_EXAR_REGB_EECK;
+
+ exar_write_reg(priv, UART_EXAR_REGB, value);
+ udelay(2);
+
+ regb = exar_read_reg(priv, UART_EXAR_REGB);
+
+ return (regb & UART_EXAR_REGB_EEDO ? 1 : 0);
+}
+
+/**
+ * exar_ee_read() - Read a word from the EEPROM
+ * @priv: Device's private structure
+ * @ee_addr: Offset of EEPROM to read word from
+ *
+ * Read a single 16bit word from an Exar UART's EEPROM
+ *
+ * Return: EEPROM word on success, negative error code on failure
+ */
+static int exar_ee_read(struct exar8250 *priv, uint8_t ee_addr)
+{
+ int i;
+ int data = 0;
+
+ exar_ee_select(priv, true);
+
+ //Send read command (opcode 110)
+ exar_ee_write_bit(priv, 1);
+ exar_ee_write_bit(priv, 1);
+ exar_ee_write_bit(priv, 0);
+
+ //Send address to read from
+ for (i = 1 << (UART_EXAR_REGB_EE_ADDR_SIZE - 1); i; i >>= 1)
+ exar_ee_write_bit(priv, (ee_addr & i));
+
+ //Read data 1 bit at a time
+ for (i = 0; i <= UART_EXAR_REGB_EE_DATA_SIZE; i++) {
+ data <<= 1;
+ data |= exar_ee_read_bit(priv);
+ }
+
+ exar_ee_select(priv, false);
+
+ return data;
+}
+
static void exar_pm(struct uart_port *port, unsigned int state, unsigned int old)
{
/*
--
2.43.2