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 09:06:54 -0400
From: Parker Newman <parker@...est.io>
To: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
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 Fri, 12 Apr 2024 13:36:42 +0300 (EEST)
Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com> wrote:

> 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 will fix all of these. 
Thanks,
-Parker