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

[Jeff Garzik]

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 <[EMAIL PROTECTED]>
---
 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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