Re: AHCI power saving (was Re: Ten hours on X60s)

Pavel Machek
2006-11-13T22:17:05Z

Hi!

> >--- a/drivers/ata/ahci.c
> >+++ b/drivers/ata/ahci.c
> >@@ -148,6 +148,8 @@ enum {
> > PORT_IRQ_PIOS_FIS | PORT_IRQ_D2H_REG_FIS,
> >
> > /* PORT_CMD bits */
> >+ PORT_CMD_ALPE = (1 << 27), /* Aggressive Link Power
> >Management Enable */
> >+ PORT_CMD_ASP = (1 << 26), /* Aggressive entrance to
> >Slumber or Partial power management states */
> > PORT_CMD_ATAPI = (1 << 24), /* Device is ATAPI */
> > PORT_CMD_LIST_ON = (1 << 15), /* cmd list DMA engine running
> > */
> > PORT_CMD_FIS_ON = (1 << 14), /* FIS DMA engine running */
> >@@ -486,7 +488,7 @@ static void ahci_power_up(void __iomem *
> > }
> >
> > /* wake up link */
> >- writel(cmd | PORT_CMD_ICC_ACTIVE, port_mmio + PORT_CMD);
> >+ writel(cmd | PORT_CMD_ICC_ACTIVE | PORT_CMD_ALPE | PORT_CMD_ASP,
> >port_mmio + PORT_CMD);
>
>
> Therein lies a key problem. Turning on all of AHCI's aggressive power
> management features DOES save a lot of power. But at the same time, it
> shortens the life of your hard drive, particularly hard drives that are
> really PATA, but have a PATA<->SATA bridge glued on the drive to enable
> connection to SATA controllers.

Well, it would be useful to do on notebooks. I believe notebook hard
drives are okay with this kind of use... Heck, I've seen notebooks
with 5 seconds of spindown time.

Anyway, I tried stopping the DMA engine when no requests are
processed. I expected to see that 1W power saving, but nothing.

ahci_stop_engine does ...

tmp = readl(port_mmio + PORT_CMD);

/* check if the HBA is idle */
if ((tmp & (PORT_CMD_START | PORT_CMD_LIST_ON)) == 0)
return 0;

/* setting HBA to idle */
tmp &= ~PORT_CMD_START;
writel(tmp, port_mmio + PORT_CMD);
printk("Stopping engine\n");

... is PORT_CMD_START that bit that was expected to save 1W?

Pavel

diff --git a/drivers/ata/ahci.c b/drivers/ata/ahci.c
index cef2e70..060d4c9 100644
--- a/drivers/ata/ahci.c
+++ b/drivers/ata/ahci.c
@@ -50,6 +50,7 @@ #include <asm/io.h>
#define DRV_NAME "ahci"
#define DRV_VERSION "2.0"

+#define POWER_SAVE

enum {
AHCI_PCI_BAR = 5,
@@ -148,6 +149,8 @@ enum {
PORT_IRQ_PIOS_FIS | PORT_IRQ_D2H_REG_FIS,

/* PORT_CMD bits */
+ PORT_CMD_ALPE = (1 << 27), /* Aggressive Link Power Management Enable */
+ PORT_CMD_ASP = (1 << 26), /* Aggressive entrance to Slumber or Partial power management states */
PORT_CMD_ATAPI = (1 << 24), /* Device is ATAPI */
PORT_CMD_LIST_ON = (1 << 15), /* cmd list DMA engine running */
PORT_CMD_FIS_ON = (1 << 14), /* FIS DMA engine running */
@@ -422,6 +425,7 @@ static int ahci_stop_engine(void __iomem
/* setting HBA to idle */
tmp &= ~PORT_CMD_START;
writel(tmp, port_mmio + PORT_CMD);
+ printk("Stopping engine\n");

/* wait for engine to stop. This could be as long as 500 msec */
tmp = ata_wait_register(port_mmio + PORT_CMD,
@@ -486,7 +490,7 @@ static void ahci_power_up(void __iomem *
}

/* wake up link */
- writel(cmd | PORT_CMD_ICC_ACTIVE, port_mmio + PORT_CMD);
+ writel(cmd | PORT_CMD_ICC_ACTIVE | PORT_CMD_ALPE | PORT_CMD_ASP, port_mmio + PORT_CMD);
}

static void ahci_power_down(void __iomem *port_mmio, u32 cap)
@@ -917,6 +921,13 @@ static void ahci_qc_prep(struct ata_queu
const u32 cmd_fis_len = 5; /* five dwords */
unsigned int n_elem;

+#ifdef POWER_SAVE
+ void __iomem *mmio = ap->host->mmio_base;
+ void __iomem *port_mmio = ahci_port_base(mmio, ap->port_no);
+
+ ahci_start_engine(port_mmio);
+#endif
+
/*
* Fill in command table information. First, the header,
* a SATA Register - Host to Device command FIS.
@@ -1029,8 +1040,15 @@ static void ahci_host_intr(struct ata_po
qc_active = readl(port_mmio + PORT_CMD_ISSUE);

rc = ata_qc_complete_multiple(ap, qc_active, NULL);
- if (rc > 0)
+ if (rc > 0) {
+#ifdef POWER_SAVE
+ void __iomem *mmio = ap->host->mmio_base;
+ void __iomem *port_mmio = ahci_port_base(mmio, ap->port_no);
+
+ ahci_stop_engine(port_mmio);
+#endif
return;
+ }
if (rc < 0) {
ehi->err_mask |= AC_ERR_HSM;
ehi->action |= ATA_EH_SOFTRESET;

--
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html