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

[Jeff Garzik <jeff@garzik.org>]

Bartlomiej Zolnierkiewicz wrote:
> 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}()! :)

May I assume you'll handle that task?  :)  It sounds like you have a far 
better idea than mine, and my main goal -- fixing bugs and warning -- is 
accomplished anyway with the merging of patch #3.

	Jeff



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