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

Ilpo Järvinen
2024-04-12T10:36:50Z

On Thu, 11 Apr 2024, parker@finest.io wrote:

> 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
> +
> +

Extra new line.

> /*
> * 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;

You could just do:
u8 value;

value = enable ? UART_EXAR_REGB_EECS : 0;

Or even:

exar_write_reg(priv, UART_EXAR_REGB, enable ? UART_EXAR_REGB_EECS : 0);
> +
> + 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

Add missing .

> + *
> + * Return: EEPROM word on success, negative error code on failure

This function does not return any -Exx code as far as I can see??

> + */
> +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;
> +}

--
i.