Re: [PATCH 2/5] i2c-i801: Move hostcfg set/reset to i801_access()

[Jean Delvare <jdelvare@suse.de>]

On Tue, 19 Jan 2016 11:09:34 -0600, minyard@acm.org wrote:
> From: Corey Minyard <cminyard@mvista.com>
> 
> The HSTCFG register save/restore was done in i2c_block_transaction,
> but all the checks were already done in i801_access, so move it into
> those checks.
> 
> Signed-off-by: Corey Minyard <cminyard@mvista.com>
> ---
>  drivers/i2c/busses/i2c-i801.c | 33 ++++++++++++++-------------------
>  1 file changed, 14 insertions(+), 19 deletions(-)

Did you test this patch?

> diff --git a/drivers/i2c/busses/i2c-i801.c b/drivers/i2c/busses/i2c-i801.c
> index 62cf1e5..9143fcf 100644
> --- a/drivers/i2c/busses/i2c-i801.c
> +++ b/drivers/i2c/busses/i2c-i801.c
> @@ -652,20 +652,6 @@ static int i801_block_transaction(struct i801_priv *priv,
>  				  int command, int hwpec)
>  {
>  	int result = 0;
> -	unsigned char hostc;
> -
> -	if (command == I2C_SMBUS_I2C_BLOCK_DATA) {
> -		if (read_write == I2C_SMBUS_WRITE) {

This is the write case...

> -			/* set I2C_EN bit in configuration register */
> -			pci_read_config_byte(priv->pci_dev, SMBHSTCFG, &hostc);
> -			pci_write_config_byte(priv->pci_dev, SMBHSTCFG,
> -					      hostc | SMBHSTCFG_I2C_EN);
> -		} else if (!(priv->features & FEATURE_I2C_BLOCK_READ)) {

... and this is the read case.

> -			dev_err(&priv->pci_dev->dev,
> -				"I2C block read is unsupported!\n");
> -			return -EOPNOTSUPP;
> -		}
> -	}
>  
>  	if (read_write == I2C_SMBUS_WRITE
>  	 || command == I2C_SMBUS_I2C_BLOCK_DATA) {
> @@ -692,11 +678,6 @@ static int i801_block_transaction(struct i801_priv *priv,
>  							     read_write,
>  							     command);
>  
> -	if (command == I2C_SMBUS_I2C_BLOCK_DATA
> -	 && read_write == I2C_SMBUS_WRITE) {
> -		/* restore saved configuration register value */
> -		pci_write_config_byte(priv->pci_dev, SMBHSTCFG, hostc);
> -	}
>  	return result;
>  }
>  
> @@ -710,6 +691,7 @@ static s32 i801_access(struct i2c_adapter *adap, u16 addr,
>  	int ret, xact = 0;
>  	struct i801_priv *priv = i2c_get_adapdata(adap);
>  	int result;
> +	int hostc = -1;
>  
>  	hwpec = (priv->features & FEATURE_SMBUS_PEC) && (flags & I2C_CLIENT_PEC)
>  		&& size != I2C_SMBUS_QUICK
> @@ -757,9 +739,19 @@ static s32 i801_access(struct i2c_adapter *adap, u16 addr,
>  		 * bit should be cleared here, even when reading */
>  		outb_p((addr & 0x7f) << 1, SMBHSTADD(priv));
>  		if (read_write == I2C_SMBUS_READ) {

However after your changes, this is the READ case...

> +			unsigned char thostc;
>  			/* NB: page 240 of ICH5 datasheet also shows
>  			 * that DATA1 is the cmd field when reading */
>  			outb_p(command, SMBHSTDAT1(priv));
> +			/* set I2C_EN bit in configuration register */
> +			pci_read_config_byte(priv->pci_dev, SMBHSTCFG, &thostc);
> +			pci_write_config_byte(priv->pci_dev, SMBHSTCFG,
> +					      thostc | SMBHSTCFG_I2C_EN);
> +			hostc = thostc;
> +		} else if (!(priv->features & FEATURE_I2C_BLOCK_READ)) {

... and this is the WRITE case. Looks very wrong.

> +			dev_err(&priv->pci_dev->dev,
> +				"I2C block read is unsupported!\n");
> +			return -EOPNOTSUPP;
>  		} else
>  			outb_p(command, SMBHSTCMD(priv));
>  		block = 1;
> @@ -795,6 +787,9 @@ static s32 i801_access(struct i2c_adapter *adap, u16 addr,
>  		outb_p(inb_p(SMBAUXCTL(priv)) &
>  		       ~(SMBAUXCTL_CRC | SMBAUXCTL_E32B), SMBAUXCTL(priv));
>  
> +	if (hostc >= 0)
> +		pci_write_config_byte(priv->pci_dev, SMBHSTCFG, hostc);
> +
>  	if (block)
>  		return ret;
>  	if (ret)

More generally, I'm only half convinced that the change is beneficial.
Yes, you avoid duplicate tests in the block case. However this is at
the expense of an initialization and a test in the common path.

I do agree that testing for unsupported functionality should be moved
back into i801_access() for consistency, as this is where the general
test for unsupported transaction types is.

-- 
Jean Delvare
SUSE L3 Support