linux-kernel - RE: [PATCH v3 4/8] pciehp: Don't disable the link permanently, during removal

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Message-ID: <bfe1b6a0b2494c71be43fea45f413575@DM2PR05MB671.namprd05.prod.outlook.com>
Date:	Thu, 9 Jan 2014 20:45:34 +0000
From:	Rajat Jain <rajatjain@...iper.net>
To:	Rajat Jain <rajatjain@...iper.net>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Rajat Jain <rajatxjain@...il.com>
CC:	Rajat Jain <rajatjain.linux@...il.com>,
	Kenji Kaneshige <kaneshige.kenji@...fujitsu.com>,
	Alex Williamson <alex.williamson@...hat.com>,
	Yijing Wang <wangyijing@...wei.com>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Yinghai Lu <yhlu.kernel@...il.com>,
	Guenter Roeck <groeck@...iper.net>,
	Yinghai Lu <yinghai@...nel.org>
Subject: RE: [PATCH v3 4/8] pciehp: Don't disable the link permanently,
 during removal

Hi Bjorn,

> -----Original Message-----
> From: linux-pci-owner@...r.kernel.org [mailto:linux-pci-
> owner@...r.kernel.org] On Behalf Of Rajat Jain
> Sent: Tuesday, January 07, 2014 10:21 AM
> To: Bjorn Helgaas; Rajat Jain
> Cc: Rajat Jain; Kenji Kaneshige; Alex Williamson; Yijing Wang; linux-
> pci@...r.kernel.org; linux-kernel@...r.kernel.org; Yinghai Lu; Guenter
> Roeck; Yinghai Lu
> Subject: RE: [PATCH v3 4/8] pciehp: Don't disable the link permanently,
> during removal
> 
> Hello Bjorn / Yinghai,
> 
> > -----Original Message-----
> > From: Bjorn Helgaas [mailto:bhelgaas@...gle.com]
> > Sent: Monday, January 06, 2014 4:04 PM
> > To: Rajat Jain
> > Cc: Rajat Jain; Kenji Kaneshige; Alex Williamson; Yijing Wang; linux-
> > pci@...r.kernel.org; linux-kernel@...r.kernel.org; Yinghai Lu; Guenter
> > Roeck; Rajat Jain; Yinghai Lu
> > Subject: Re: [PATCH v3 4/8] pciehp: Don't disable the link
> > permanently, during removal
> >
> > On Sun, Jan 5, 2014 at 10:53 AM, Rajat Jain <rajatxjain@...il.com>
> > wrote:
> > > Hello Bjorn,
> > >
> > > Just checking on the fate of this patch set...
> > >
> > > On Tue, Dec 17, 2013 at 5:02 PM, Bjorn Helgaas <bhelgaas@...gle.com>
> > wrote:
> > >> [+cc yinghai@...nel.org (seems to be Yinghai's preferred email]
> > >>
> > >> On Tue, Dec 17, 2013 at 12:06:05PM -0800, Rajat Jain wrote:
> > >>> We need future link up events for hot-add, thus don't disable the
> > >>> link permanently during device removal. Also, remove the static
> > >>> functions that are now left unused.
> > >>
> > >> The changelog should mention that this reverts part of 2debd9289997
> > ("PCI:
> > >> pciehp: Disable/enable link during slot power off/on").
> > >
> > > Sure. Do you want me to submit another patch set (bumping up the
> > > version) with this change log, or you'd want to add this change log
> > > while merging?
> > >
> > >>
> > >> Yinghai, can you tell us whether this is an issue on your systems?
> > >
> > > As Yinghai confirms further down this thread, his issue was
> > > confirmed by Intel to be a bug in the repeater chip.
> > > ----------------------------------
> > > Yinghai writes:
> > >> According to HW guys and Intel, that should be bug of repeater.
> > >>
> > > ---------------------------------
> > >  I don't know about the details of his scenario, except that when
> > > the adapter was disabled the repeater kept on flapping the link up &
> > > down (and hence disabling the link solved the problem then). Yinghai
> > > couldn't test, but I believe with this patch even if we disable
> > > presence detect interrupt, the "adapter present / no present"
> > > messages would (rightly) convert to "Link Up / Link Down" messages
> > > (since the repeater keeps on flapping the link).
> > >
> > > Since it is a platform specific bug, I'm not sure what can be done
> > > to remove those messages except may be reduce the verbosity? If
> > > you'd like I could change all the INFO messages to DBG messages.
> >
> > Even if it's a defect in a particular piece of hardware, I don't want
> > to regress on that hardware, even if the regression is just extra
> > messages that we didn't see before.
> >
> > I think ideally we would add some sort of quirk for that hardware so
> > it works just as well as it does today.  I think extra messages will
> > lead to a bug reports from users.
> 
> Sure, I can do that. I think what the quirk would have to do is that for
> that particular platform, don't enable the link-state based hotplug.
> (Since link-state hotplug will not work if we disable the link
> permanently as we do today on card removal).
> 
> But the question is how to determine that the quirk has to be applied? I
> think the objective is to apply the quirk to the platforms that have a
> "PCIe repeater". Since this does not depend on a PCI device / vendor ID,
> and I think the PCIe repeater is probably not even visible to the pciehp
> or the PCI subsystem, how do I determine that the quirk has to be
> applied?

Any ideas on how do I identify the platforms that may have this problem? 

Thanks,

Rajat


> 
> If (hw_has_pcie_repeater)
> 	Don't use link-state hotplug (and disable link permanently during
> card removal) Else
> 	Use link-state hotplug (and don't disable the link permanently)
> 
> 
> Yinghai: Since I do not have that hardware, I will need some help in
> testing the patch with the quirk. I was wondering if you'd still have
> that hardware around and would be able to help me with testing?
> 
> Thanks,
> 
> Rajat
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