Re: [PATCH 6/8] i2c: i801: add i801_single_transaction(), complementing i801_block_transaction()

[Jean Delvare <jdelvare@suse.de>]

Hi Heiner,

On Fri, 15 Apr 2022 18:58:03 +0200, Heiner Kallweit wrote:
> This patch factors out non-block pre/post processing to a new function
> i801_single_transaction(), complementing existing function
> i801_block_transaction(). This makes i801_access() better readable.

I like the idea, but I have objections about some implementation
details, see below.

> Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
> ---
>  drivers/i2c/busses/i2c-i801.c | 95 +++++++++++++++++++++--------------
>  1 file changed, 58 insertions(+), 37 deletions(-)
> 
> diff --git a/drivers/i2c/busses/i2c-i801.c b/drivers/i2c/busses/i2c-i801.c
> index bf77f8640..8c2245f38 100644
> --- a/drivers/i2c/busses/i2c-i801.c
> +++ b/drivers/i2c/busses/i2c-i801.c
> @@ -771,6 +771,62 @@ static int i801_block_transaction(struct i801_priv *priv, union i2c_smbus_data *
>  	return result;
>  }
>  
> +/* Single transaction function */

The term "single transaction" is a bit misleading. Block transactions
are also single transactions, in the sense that there's one start
condition at the beginning and one stop condition at the end. I'd
rather call non-block transactions "single value transactions" or
"simple transactions".

> +static int i801_single_transaction(struct i801_priv *priv, union i2c_smbus_data *data,
> +				   char read_write, int command)
> +{
> +	int xact, ret;
> +
> +	switch (command) {
> +	case I2C_SMBUS_QUICK:
> +		xact = I801_QUICK;
> +		break;
> +	case I2C_SMBUS_BYTE:
> +                xact = I801_BYTE;
> +                break;

Previous 2 lines are indented with spaces instead of tabs.

> +	case I2C_SMBUS_BYTE_DATA:
> +		if (read_write == I2C_SMBUS_WRITE)
> +			outb_p(data->byte, SMBHSTDAT0(priv));
> +		xact = I801_BYTE_DATA;
> +		break;
> +	case I2C_SMBUS_WORD_DATA:
> +		if (read_write == I2C_SMBUS_WRITE) {
> +			outb_p(data->word & 0xff, SMBHSTDAT0(priv));
> +			outb_p((data->word & 0xff00) >> 8, SMBHSTDAT1(priv));
> +		}
> +		xact = I801_WORD_DATA;
> +		break;
> +	case I2C_SMBUS_PROC_CALL:
> +		outb_p(data->word & 0xff, SMBHSTDAT0(priv));
> +		outb_p((data->word & 0xff00) >> 8, SMBHSTDAT1(priv));
> +		xact = I801_PROC_CALL;
> +		break;
> +	default:
> +		return -EOPNOTSUPP;

That's never going to happen.

Generally speaking, I'm worried about having the same switch/case
construct here that we already have in i801_access. Looks to me like we
are doing half of the work here and the other half there and I fail to
see the rationale for splitting the work like that. I mean, I see how
it solves the asymmetry between the block and non-block code paths, but
the result doesn't look appealing. From a performance perspective it's
questionable too.

What prevents us from doing all the work on either side? Maybe we
should move more code into i801_single_transaction (possibly in a
subsequent patch)?

> +	}
> +
> +	ret = i801_transaction(priv, xact);
> +

Traditionally no blank line here.

> +	if (ret || read_write == I2C_SMBUS_WRITE)
> +		return ret;
> +
> +	switch (command) {
> +	case I2C_SMBUS_BYTE:
> +	case I2C_SMBUS_BYTE_DATA:
> +		data->byte = inb_p(SMBHSTDAT0(priv));
> +		break;
> +	case I2C_SMBUS_WORD_DATA:
> +	case I2C_SMBUS_PROC_CALL:
> +		data->word = inb_p(SMBHSTDAT0(priv)) +
> +			     (inb_p(SMBHSTDAT1(priv)) << 8);
> +		break;
> +	default:
> +		break;

Default case is not needed.

> +	}
> +
> +	return 0;
> +}
> +
>  static void i801_set_hstadd(struct i801_priv *priv, u8 addr, char read_write)
>  {
>  	addr <<= 1;
> @@ -784,9 +840,7 @@ static s32 i801_access(struct i2c_adapter *adap, u16 addr,
>  		       unsigned short flags, char read_write, u8 command,
>  		       int size, union i2c_smbus_data *data)
>  {
> -	int hwpec;
> -	int block = 0;
> -	int ret, xact;
> +	int hwpec, ret, block = 0;
>  	struct i801_priv *priv = i2c_get_adapdata(adap);
>  
>  	mutex_lock(&priv->acpi_lock);
> @@ -804,36 +858,23 @@ static s32 i801_access(struct i2c_adapter *adap, u16 addr,
>  	switch (size) {
>  	case I2C_SMBUS_QUICK:
>  		i801_set_hstadd(priv, addr, read_write);
> -		xact = I801_QUICK;
>  		break;
>  	case I2C_SMBUS_BYTE:
>  		i801_set_hstadd(priv, addr, read_write);
>  		if (read_write == I2C_SMBUS_WRITE)
>  			outb_p(command, SMBHSTCMD(priv));
> -		xact = I801_BYTE;
>  		break;
>  	case I2C_SMBUS_BYTE_DATA:
>  		i801_set_hstadd(priv, addr, read_write);
>  		outb_p(command, SMBHSTCMD(priv));
> -		if (read_write == I2C_SMBUS_WRITE)
> -			outb_p(data->byte, SMBHSTDAT0(priv));
> -		xact = I801_BYTE_DATA;
>  		break;
>  	case I2C_SMBUS_WORD_DATA:
>  		i801_set_hstadd(priv, addr, read_write);
>  		outb_p(command, SMBHSTCMD(priv));
> -		if (read_write == I2C_SMBUS_WRITE) {
> -			outb_p(data->word & 0xff, SMBHSTDAT0(priv));
> -			outb_p((data->word & 0xff00) >> 8, SMBHSTDAT1(priv));
> -		}
> -		xact = I801_WORD_DATA;
>  		break;
>  	case I2C_SMBUS_PROC_CALL:
>  		i801_set_hstadd(priv, addr, I2C_SMBUS_WRITE);
>  		outb_p(command, SMBHSTCMD(priv));
> -		outb_p(data->word & 0xff, SMBHSTDAT0(priv));
> -		outb_p((data->word & 0xff00) >> 8, SMBHSTDAT1(priv));
> -		xact = I801_PROC_CALL;
>  		read_write = I2C_SMBUS_READ;
>  		break;
>  	case I2C_SMBUS_BLOCK_DATA:
> @@ -883,7 +924,7 @@ static s32 i801_access(struct i2c_adapter *adap, u16 addr,
>  	if (block)
>  		ret = i801_block_transaction(priv, data, read_write, size);
>  	else
> -		ret = i801_transaction(priv, xact);
> +		ret = i801_single_transaction(priv, data, read_write, size);
>  
>  	/* Some BIOSes don't like it when PEC is enabled at reboot or resume
>  	   time, so we forcibly disable it after every transaction. Turn off
> @@ -891,26 +932,6 @@ static s32 i801_access(struct i2c_adapter *adap, u16 addr,
>  	if (hwpec || block)
>  		outb_p(inb_p(SMBAUXCTL(priv)) &
>  		       ~(SMBAUXCTL_CRC | SMBAUXCTL_E32B), SMBAUXCTL(priv));
> -
> -	if (block)
> -		goto out;
> -	if (ret)
> -		goto out;
> -	if ((read_write == I2C_SMBUS_WRITE) || (xact == I801_QUICK))
> -		goto out;
> -
> -	switch (xact) {
> -	case I801_BYTE:	/* Result put in SMBHSTDAT0 */
> -	case I801_BYTE_DATA:
> -		data->byte = inb_p(SMBHSTDAT0(priv));
> -		break;
> -	case I801_WORD_DATA:
> -	case I801_PROC_CALL:
> -		data->word = inb_p(SMBHSTDAT0(priv)) +
> -			     (inb_p(SMBHSTDAT1(priv)) << 8);
> -		break;
> -	}
> -
>  out:
>  	/*
>  	 * Unlock the SMBus device for use by BIOS/ACPI,


-- 
Jean Delvare
SUSE L3 Support