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

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Date: Fri, 12 Apr 2024 13:36:42 +0300 (EEST)
From: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
To: parker@...est.io
cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>, 
    Jiri Slaby <jirislaby@...nel.org>, linux-kernel@...r.kernel.org, 
    linux-serial@...r.kernel.org, Parker Newman <pnewman@...necttech.com>
Subject: Re: [PATCH v2 2/7] serial: exar: add support for reading from Exar
 EEPROM

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

> From: Parker Newman <pnewman@...necttech.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@...necttech.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.