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

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Date:	Mon, 13 Nov 2006 15:22:19 +0100
From:	Pavel Machek <pavel@....cz>
To:	John Fremlin <not@...t.any.name>
Cc:	kernel list <linux-kernel@...r.kernel.org>, htejun@...il.com,
	jim.kardach@...el.com, ak@...e.de
Subject: AHCI power saving (was Re: Ten hours on X60s)

Hi!

> There are a couple of bits for turning on the hardware's
> power-saving. It makes me think it might save me about a watt, but the
> effect could be entirely psychological.

No, I did not mean _those_ bits. This made little or difference for
me... (100mW or so, definitely not watt).

doing ahci_pci_device_{suspend,resume} should definitely do the trick,
and ahci_{start,stop}_engine might be enough.

> Here is the patch. It is not correct and ready for general use,
> because you are supposed to check whether the AHCI chipset supports
> the feature.

> So there is no example code for sending the AHCI chipset to S3 and
> bringing it back? I thought you said there was before, but I can't
> find it!

ahci_pci_device_{suspend,resume} seems to be the code...

Here's the port of your patch to recent -git.
								Pavel

diff --git a/drivers/ata/ahci.c b/drivers/ata/ahci.c
index cef2e70..82a8a44 100644
--- 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);
 }
 
 static void ahci_power_down(void __iomem *port_mmio, u32 cap)

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