Re: [PATCH v2 3/5] i2c-piix4: Request base address index region once for SB800

[Mika Westerberg <mika.westerberg@linux.intel.com>]

On Sun, Nov 01, 2015 at 05:32:07PM +0100, Christian Fetzer wrote:
> Request the SMBus base address index region once in piix4_probe. This
> is particularly useful when using the multiplexed adapter in SB800 as
> it avoids requesting and releasing the region on every transfer.
> 
> Signed-off-by: Christian Fetzer <fetzer.ch@gmail.com>
> ---
>  drivers/i2c/busses/i2c-piix4.c | 35 ++++++++++++++++++++++-------------
>  1 file changed, 22 insertions(+), 13 deletions(-)
> 
> diff --git a/drivers/i2c/busses/i2c-piix4.c b/drivers/i2c/busses/i2c-piix4.c
> index 35eeb0d..d866b58 100644
> --- a/drivers/i2c/busses/i2c-piix4.c
> +++ b/drivers/i2c/busses/i2c-piix4.c
> @@ -125,6 +125,9 @@ static const struct dmi_system_id piix4_dmi_ibm[] = {
>  	{ },
>  };
>  
> +/* SB800 globals */
> +static unsigned short piix4_smb_idx_sb800;
> +
>  struct i2c_piix4_adapdata {
>  	unsigned short smba;
>  };
> @@ -232,7 +235,6 @@ static int piix4_setup_sb800(struct pci_dev *PIIX4_dev,
>  			     const struct pci_device_id *id, u8 aux)
>  {
>  	unsigned short piix4_smba;
> -	unsigned short smba_idx = 0xcd6;
>  	u8 smba_en_lo, smba_en_hi, smb_en, smb_en_status;
>  	u8 i2ccfg, i2ccfg_offset = 0x10;
>  
> @@ -254,16 +256,10 @@ static int piix4_setup_sb800(struct pci_dev *PIIX4_dev,
>  	else
>  		smb_en = (aux) ? 0x28 : 0x2c;
>  
> -	if (!request_region(smba_idx, 2, "smba_idx")) {
> -		dev_err(&PIIX4_dev->dev, "SMBus base address index region "
> -			"0x%x already in use!\n", smba_idx);
> -		return -EBUSY;
> -	}
> -	outb_p(smb_en, smba_idx);
> -	smba_en_lo = inb_p(smba_idx + 1);
> -	outb_p(smb_en + 1, smba_idx);
> -	smba_en_hi = inb_p(smba_idx + 1);
> -	release_region(smba_idx, 2);
> +	outb_p(smb_en, piix4_smb_idx_sb800);
> +	smba_en_lo = inb_p(piix4_smb_idx_sb800 + 1);
> +	outb_p(smb_en + 1, piix4_smb_idx_sb800);
> +	smba_en_hi = inb_p(piix4_smb_idx_sb800 + 1);
>  
>  	if (!smb_en) {
>  		smb_en_status = smba_en_lo & 0x10;
> @@ -616,16 +612,26 @@ static int piix4_add_adapter(struct pci_dev *dev, unsigned short smba,
>  
>  static int piix4_probe(struct pci_dev *dev, const struct pci_device_id *id)
>  {
> +	unsigned short smba_idx = 0xcd6;
>  	int retval;
>  
>  	if ((dev->vendor == PCI_VENDOR_ID_ATI &&
>  	     dev->device == PCI_DEVICE_ID_ATI_SBX00_SMBUS &&
>  	     dev->revision >= 0x40) ||
> -	    dev->vendor == PCI_VENDOR_ID_AMD)
> +	    dev->vendor == PCI_VENDOR_ID_AMD) {
> +
> +		if (!request_region(smba_idx, 2, "smba_idx")) {
> +			dev_err(&dev->dev, "SMBus base address index region "
> +				"0x%x already in use!\n", smba_idx);
> +			return -EBUSY;
> +		}
> +		piix4_smb_idx_sb800 = smba_idx;

If I read this right, piix4_smb_idx_sb800 will always be 0xcd6. Why do
you need the global variable at all then? Why not have constant like
below?

#define	SB800_PIIX4_SMB_IDX 0xcd6