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

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Date:	Wed, 23 Jan 2008 10:26:28 -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 Wed, Jan 23, 2008 at 10:20:54AM +0800, Shaohua Li wrote:
> 
> On Tue, 2008-01-22 at 14:58 -0800, Greg KH wrote:
> > 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.
> The structure is just for internal use of ASPM, just don't want make it
> global.

Yes, you don't need to expose the structure type, just name it, and then
define it in the code itself.

But using a void pointer as you have here, allows you to assign two
different types of structures to this pointer.  Are you sure that you
always get this right?  :)

Please, let's try to inforce type-saftey and set this to be a specific
type of pointer to a structure.  That will require you to possibly merge
the two structures, which will require some code changes.

thanks,

greg k-h
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