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Date: Thu, 25 Oct 2007 22:01:58 +0200
From: Bartlomiej Zolnierkiewicz <bzolnier@...il.com>
To: Jeff Garzik <jeff@...zik.org>
Cc: LKML <linux-kernel@...r.kernel.org>, linux-ide@...r.kernel.org,
akpm@...ux-foundation.org
Subject: Re: [PATCH 2/3] drivers/ide/pci/sc1200.c: remove pointless hwif lookup loop
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@...hat.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[] = {
-
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