Re: [PATCH 2/3] drivers/ide/pci/sc1200.c: remove pointless hwif lookup loop

[Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>]

On Thursday 25 October 2007, Jeff Garzik wrote:
> Store our hwif indices at probe time, in order to eliminate a needless
> and ugly loop across all hwifs, searching for our pci device.

It seems that we can simplify it even further and remove knowledge about
hwifs altogether from suspend/resume methods.

> Signed-off-by: Jeff Garzik <jgarzik@redhat.com>
> ---
>  drivers/ide/pci/sc1200.c |   76 +++++++++++++++++++++++++++++++---------------
>  1 files changed, 51 insertions(+), 25 deletions(-)
> 
> diff --git a/drivers/ide/pci/sc1200.c b/drivers/ide/pci/sc1200.c
> index d2c8b55..17e58d6 100644
> --- a/drivers/ide/pci/sc1200.c
> +++ b/drivers/ide/pci/sc1200.c
> @@ -41,6 +41,8 @@
>  #define PCI_CLK_66	0x02
>  #define PCI_CLK_33A	0x03
>  
> +#define SC1200_IFS	4
> +
>  static unsigned short sc1200_get_pci_clock (void)
>  {
>  	unsigned char chip_id, silicon_revision;
> @@ -261,31 +263,32 @@ static void sc1200_set_pio_mode(ide_drive_t *drive, const u8 pio)
>  }
>  
>  #ifdef CONFIG_PM
> -static ide_hwif_t *lookup_pci_dev (ide_hwif_t *prev, struct pci_dev *dev)
> -{
> -	int	h;
> -
> -	for (h = 0; h < MAX_HWIFS; h++) {
> -		ide_hwif_t *hwif = &ide_hwifs[h];
> -		if (prev) {
> -			if (hwif == prev)
> -				prev = NULL;	// found previous, now look for next match
> -		} else {
> -			if (hwif && hwif->pci_dev == dev)
> -				return hwif;	// found next match
> -		}
> -	}
> -	return NULL;	// not found
> -}
> -
>  typedef struct sc1200_saved_state_s {
>  	__u32		regs[4];
>  } sc1200_saved_state_t;
>  
> +static unsigned int pack_hwif_idx(u8 *idx)
> +{
> +	return	(((unsigned int) idx[0]) << 0) |
> +		(((unsigned int) idx[1]) << 8) |
> +		(((unsigned int) idx[2]) << 16) |
> +		(((unsigned int) idx[3]) << 24);
> +}
> +
> +static ide_hwif_t *sc1200_hwif(struct pci_dev *pdev, unsigned int iface)
> +{
> +	unsigned int packed_hwifs, idx;
> +
> +	packed_hwifs = (unsigned long) pci_get_drvdata(pdev);
> +	idx = (packed_hwifs >> (iface * 8)) & 0xff;
> +
> +	return (idx == 0xff) ? NULL : &ide_hwifs[idx];
> +}
>  
>  static int sc1200_suspend (struct pci_dev *dev, pm_message_t state)
>  {
> -	ide_hwif_t		*hwif = NULL;
> +	ide_hwif_t		*hwif;
> +	int			i;
>  
>  	printk("SC1200: suspend(%u)\n", state.event);
>  
> @@ -295,9 +298,14 @@ static int sc1200_suspend (struct pci_dev *dev, pm_message_t state)
>  		//
>  		// Loop over all interfaces that are part of this PCI device:
>  		//
> -		while ((hwif = lookup_pci_dev(hwif, dev)) != NULL) {
> +		for (i = 0; i < SC1200_IFS; i++) {
>  			sc1200_saved_state_t	*ss;
>  			unsigned int		basereg, r;
> +
> +			hwif = sc1200_hwif(dev, i);
> +			if (!hwif)
> +				continue;
> +
>  			//
>  			// allocate a permanent save area, if not already allocated
>  			//
> @@ -310,7 +318,7 @@ static int sc1200_suspend (struct pci_dev *dev, pm_message_t state)
>  			}
>  			ss = (sc1200_saved_state_t *)hwif->config_data;
>  			//
> -			// Save timing registers:  this may be unnecessary if 
> +			// Save timing registers:  this may be unnecessary if
>  			// BIOS also does it
>  			//
>  			basereg = hwif->channel ? 0x50 : 0x40;

Please take a close look at the line above and the next three lines:

for (r = 0; r < 4; ++r) {
	pci_read_config_dword (hwif->pci_dev, basereg + (r<<2), &ss->regs[r]);
}

It is highly obfuscated but the sc1200_suspend() reads 16 bytes from
the offset 0x40 (for the primary port) and puts them in the corresponding
struct sc1200_saved_state_s buffer, then it reads another 16 bytes from the
offset 0x50 (for the secondary port) and puts it in the another buffer.

In summary sc1200_suspend() reads 32 continuous bytes from offset 0x40
and the exactly reverse operation happens in sc1200_resume().

Given that and the fact that struct sc1200_save_state_s buffers are used
_only_ by sc1200_{suspend,resume}() we may safely convert the code to use
one buffer for both ports (the whole PCI device).  We just need to bump
the size of struct sc1200_saved_state_s (from 4 to 8 double-words) and use
pci_{get,set}_drvdata() instead of hwif->config_data.  Then we can remove
looping over interfaces completely from sc1200_{suspend,resume}()! :)

> @@ -320,7 +328,7 @@ static int sc1200_suspend (struct pci_dev *dev, pm_message_t state)
>  		}
>  	}
>  
> -	/* You don't need to iterate over disks -- sysfs should have done that for you already */ 
> +	/* You don't need to iterate over disks -- sysfs should have done that for you already */
>  
>  	pci_disable_device(dev);
>  	pci_set_power_state(dev, pci_choose_state(dev, state));
> @@ -330,7 +338,8 @@ static int sc1200_suspend (struct pci_dev *dev, pm_message_t state)
>  
>  static int sc1200_resume (struct pci_dev *dev)
>  {
> -	ide_hwif_t	*hwif = NULL;
> +	ide_hwif_t		*hwif;
> +	int			i;
>  
>  	pci_set_power_state(dev, PCI_D0);	// bring chip back from sleep state
>  	dev->current_state = PM_EVENT_ON;
> @@ -338,9 +347,15 @@ static int sc1200_resume (struct pci_dev *dev)
>  	//
>  	// loop over all interfaces that are part of this pci device:
>  	//
> -	while ((hwif = lookup_pci_dev(hwif, dev)) != NULL) {
> +	for (i = 0; i < SC1200_IFS; i++) {
>  		unsigned int		basereg, r;
> -		sc1200_saved_state_t	*ss = (sc1200_saved_state_t *)hwif->config_data;
> +		sc1200_saved_state_t	*ss;
> +
> +		hwif = sc1200_hwif(dev, i);
> +		if (!hwif)
> +			continue;
> +
> +		ss = (sc1200_saved_state_t *)hwif->config_data;
>  
>  		//
>  		// Restore timing registers:  this may be unnecessary if BIOS also does it
> @@ -386,7 +401,18 @@ static const struct ide_port_info sc1200_chipset __devinitdata = {
>  
>  static int __devinit sc1200_init_one(struct pci_dev *dev, const struct pci_device_id *id)
>  {
> -	return ide_setup_pci_device(dev, &sc1200_chipset);
> +	unsigned int packed_hwifs;
> +	int rc;
> +	u8 idx[4] = { 0xff, 0xff, 0xff, 0xff };
> +
> +	rc = __ide_setup_pci_device(dev, &sc1200_chipset, &idx[0]);
> +	if (rc)
> +		return rc;
> +	
> +	packed_hwifs = pack_hwif_idx(&idx[0]);
> +
> +	pci_set_drvdata(dev, (void *)(unsigned long) packed_hwifs);
> +	return 0;
>  }
>  
>  static const struct pci_device_id sc1200_pci_tbl[] = {