linux-kernel - Re: [RFC v2 3/5] PCIe, Add runtime PM support to PCIe port

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Date:	Fri, 4 May 2012 22:55:13 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Bjorn Helgaas <bhelgaas@...gle.com>
Cc:	Huang Ying <ying.huang@...el.com>, ming.m.lin@...el.com,
	linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
	Zheng Yan <zheng.z.yan@...el.com>
Subject: Re: [RFC v2 3/5] PCIe, Add runtime PM support to PCIe port

On Friday, May 04, 2012, Bjorn Helgaas wrote:
> On Fri, May 4, 2012 at 2:13 AM, Huang Ying <ying.huang@...el.com> wrote:
> > From: Zheng Yan <zheng.z.yan@...el.com>
> >
> > This patch adds runtime PM support to PCIe port.  This is needed by
> > PCIe D3cold support, where PCIe device in slot may be powered on/off
> > by PCIe port.
> 
> I assume this works for integrated PCIe devices as well as those that
> are plugged into a slot and can be physically removed -- maybe the
> text "in slot" is superfluous?
> 
> > Because runtime suspend is broken for some chipset, a white list is
> > used to enable runtime PM support for only chipset known to work.
> 
> A whitelist requires perpetual maintenance.  Every time a new working
> chipset comes out, you have to update the whitelist.  That doesn't
> seem right.

Well, we can't possibly enable the feature for all PCIe ports in existence
either, because some of them will not work with it (almost surely).

Thanks,
Rafael
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