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

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Date:	Tue, 22 Jan 2008 14:58:06 -0800
From:	Greg KH <greg@...ah.com>
To:	Shaohua Li <shaohua.li@...el.com>
Cc:	lkml <linux-kernel@...r.kernel.org>,
	linux-pci <linux-pci@...ey.karlin.mff.cuni.cz>,
	"Pallipadi, Venkatesh" <venkatesh.pallipadi@...el.com>,
	"Kok, Auke" <auke-jan.h.kok@...el.com>,
	Matthew Wilcox <matthew@....cx>
Subject: Re: [PATCH]PCIE ASPM support - takes 3

On Fri, Jan 18, 2008 at 09:56:28AM +0800, Shaohua Li wrote:
> v3->v2, fixed the issues Matthew Wilcox raised.
> 
> 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.

Can you please fix up all of the warnings that checkpatch.pl and sparse
produce from this patch?

Also, one small thing:

> --- linux.orig/include/linux/pci.h	2008-01-16 15:59:42.000000000 +0800
> +++ linux/include/linux/pci.h	2008-01-18 09:41:20.000000000 +0800
> @@ -164,6 +164,10 @@ struct pci_dev {
>  					   this is D0-D3, D0 being fully functional,
>  					   and D3 being off. */
>  
> +#ifdef CONFIG_PCIEASPM
> +	void		*link_state;	/* ASPM link state. */
> +#endif

Can we make this a "real" pointer to a structure?  I note that you use
two different structures here in this pointer, should you really do
that?  It's good to get type-checks whereever possible.

thanks,

greg k-h
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