linux-kernel - Re: [RFC] PCIE ASPM support

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Date:	Tue, 08 Jan 2008 09:02:35 +1100
From:	Michael Ellerman <michael@...erman.id.au>
To:	Shaohua Li <shaohua.li@...el.com>
Cc:	lkml <linux-kernel@...r.kernel.org>,
	linux-pci <linux-pci@...ey.karlin.mff.cuni.cz>,
	Greg KH <greg@...ah.com>,
	"Pallipadi, Venkatesh" <venkatesh.pallipadi@...el.com>
Subject: Re: [RFC] PCIE ASPM support

On Thu, 2008-01-03 at 14:15 +0800, Shaohua Li wrote:
> PCI Express ASPM defines a protocol for PCI Express components in the D0
> state to reduce Link power by placing their Links into a low power state
> and instructing the other end of the Link to do likewise. This
> capability allows hardware-autonomous, dynamic Link power reduction
> beyond what is achievable by software-only controlled power management.
> However, The device should be configured by software appropriately.
> Enabling ASPM will save power, but will introduce device latency.
> 
> This patch adds ASPM support in Linux. It introduces a global policy for
> ASPM, a sysfs file /sys/module/pcie_aspm/parameters/policy can control
> it. The interface can be used as a boot option too. Currently we have
> below setting:
> 	-default, BIOS default setting
> 	-powersave, highest power saving mode, enable all available ASPM state
> and clock power management
> 	-performance, highest performance, disable ASPM and clock power
> management
> By default, the 'default' policy is used currently.
> 
> In my test, power difference between powersave mode and performance mode
> is about 1.3w in a system with 3 PCIE links.
> 
> please review, any comments will be appreciated.
> 
> Signed-off-by: Shaohua Li <shaohua.li@...el.com>

Minor nit, but you do a lot of these:

+	return ((struct link_state *)pdev->link_state)->bios_aspm_state;
+	return ((struct link_state *)pdev->link_state)->bios_clk_state;
+	((struct link_state*)pdev->link_state)->clk_pm_enabled = !!enable;
+	((struct link_state*)pdev->link_state)->clk_pm_capable = capable;
+	((struct link_state*)pdev->link_state)->clk_pm_enabled = enabled;
+	((struct link_state*)pdev->link_state)->bios_clk_state = enabled;
+	((struct link_state *)pdev->link_state)->enabled_state = state;
+	if (((struct link_state *)pdev->link_state)->support_state == 0)
+	if (((struct link_state *)pdev->link_state)->enabled_state == state)
+	((struct link_state *)pdev->link_state)->enabled_state);

Which is a little hard on the eye.

cheers

-- 
Michael Ellerman
OzLabs, IBM Australia Development Lab

wwweb: http://michael.ellerman.id.au
phone: +61 2 6212 1183 (tie line 70 21183)

We do not inherit the earth from our ancestors,
we borrow it from our children. - S.M.A.R.T Person

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