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

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Date:	Mon, 13 Nov 2006 10:32:24 -0500
From:	Jeff Garzik <jeff@...zik.org>
To:	Pavel Machek <pavel@....cz>
CC:	John Fremlin <not@...t.any.name>,
	kernel list <linux-kernel@...r.kernel.org>, htejun@...il.com,
	jim.kardach@...el.com, ak@...e.de
Subject: Re: AHCI power saving (was Re: Ten hours on X60s)

Pavel Machek wrote:
> --- 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.

	Jeff


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