Rajat,
After read almost all the proposed material you mentioned, got
some of my points here for you and other guru's reference.
1. It is not totally out of spec, most of it have been described
in PCIe spec 3.0 section 6.7.3.3. Data Link Layer State Changed
Events.
2. if it works on your hardware, none could stop you, because you
didn't hurt anybody, that is not evil at all !
3. Introduce link status event as replacement to all other
existed machinism is too aggressive that will make us lose some other
features of PCIe hotplug. for example, attention button let system
and user have time to make preparation and undo. presence bit is
confirmation to system etc. someone like me would say no if it would
be replacement while not an additament.
4. Just as Bjorn mentioned, don't break it and 'fix' it, try to
make a complete and well formed , more important --- considered design
for all things, the existing and the one you would like introduce. it
is welcome.
Thanks,
Ethan
On Tue, Dec 10, 2013 at 2:46 AM, Rajat Jain <rajatjain@xxxxxxxxxxx> wrote:
> Hello,
>
>> -----Original Message-----
>> From: linux-pci-owner@xxxxxxxxxxxxxxx [mailto:linux-pci-
>> owner@xxxxxxxxxxxxxxx] On Behalf Of Ethan Zhao
>> Sent: Sunday, December 08, 2013 6:10 PM
>> To: Rajat Jain
>> Cc: Bjorn Helgaas; Yinghai Lu; linux-pci@xxxxxxxxxxxxxxx; Kenji
>> Kaneshige; stable@xxxxxxxxxxxxxxx
>> Subject: Re: [PATCH] PCI, pciehp: Turn on link a while to workaround
>> presense detection
>>
>> Rajat,
>>
>> Do you have a draft to extend the hotplug spec ? seem you wanna
>> introduce link change interrupt to the your chip or just poll the link
>> status register ?
>
> This is for the systems that do not implement elements like attention button:
>
> http://www.spinics.net/lists/hotplug/msg05802.html
> (Inspiration from the thread: http://www.spinics.net/lists/linux-pci/msg05783.html)
>
>
> Here was the proposed minimal patch:
>
> http://marc.info/?l=linux-pci&m=138610993912921&w=2
> http://marc.info/?t=138611014300001&r=1&w=2
>
> Would appreciate any review comments.
>
> Thanks,
>
> Rajat
>
>
>>
>> Thanks,
>> Ethan
>>
>> On Mon, Dec 9, 2013 at 5:29 AM, Rajat Jain <rajatjain@xxxxxxxxxxx>
>> wrote:
>> > Hello,
>> >
>> >> -----Original Message-----
>> >> From: linux-pci-owner@xxxxxxxxxxxxxxx [mailto:linux-pci-
>> >> owner@xxxxxxxxxxxxxxx] On Behalf Of Bjorn Helgaas
>> >> Sent: Saturday, December 07, 2013 10:36 AM
>> >> To: Yinghai Lu
>> >> Cc: linux-pci@xxxxxxxxxxxxxxx; Kenji Kaneshige;
>> >> stable@xxxxxxxxxxxxxxx
>> >> Subject: Re: [PATCH] PCI, pciehp: Turn on link a while to workaround
>> >> presense detection
>> >>
>> >> On Fri, Dec 6, 2013 at 1:22 PM, Yinghai Lu <yinghai@xxxxxxxxxx>
>> wrote:
>> >> > During hotplug test on platform, found slot status register does
>> >> > not report present status correctly. That present bit does not get
>> >> > cleared even after that card is removed.
>> >> >
>> >> > That problem is caused by commit:
>> >> > | commit 2debd9289997fc5d1c0043b41201a8b40d5e11d0
>> >> > |
>> >> > | PCI: pciehp: Disable/enable link during slot power off/on
>> >> >
>> >> > It looks like chipset bug, that PresDet bit is "OR" operation
>> >> > between sideband input from FPGA, and chipset inband detection from
>> pcie link.
>> >>
>> >> This doesn't sound like a chipset bug. It sounds like exactly what
>> >> the spec describes: "Presence Detect State - This bit indicates the
>> >> presence of an adapter in the slot, reflected by the logical "OR" of
>> >> the Physical Layer in-band presence detect mechanism and, if present,
>> >> any out-of-band presence detect mechanism defined for the slot's
>> >> corresponding form factor" (PCIe 3.0, sec 7.8.11).
>> >>
>> >> So I want to fix this pciehp problem, but between 2debd9289997 and
>> >> this patch, pciehp_power_off_slot() is accumulating warts that make
>> >> it look like we're just reacting to things that break rather than
>> >> making a robust design to start with.
>> >
>> > Yes.
>> >
>> > In fact things do get more complicated if we introduce link state
>> based hot-plug, because then that requires that we do NOT disable the
>> link permanently during power off. (Because we would want to receive
>> future hot-plug link-up events).
>> >
>> >>
>> >> > It does not like if we disable pcie link at first and power off
>> >> > other side device, and it has input from inband detection always 1.
>> >> >
>> >> > Workaround: Try turn on link a while after power off.
>> >> >
>> >> > After this patch, PresDet report correct status when removing or
>> >> > adding card later.
>> >> >
>> >> > Signed-off-by: Yinghai Lu <yinghai@xxxxxxxxxx>
>> >> > Cc: Kenji Kaneshige <kaneshige.kenji@xxxxxxxxxxxxxx>
>> >> > Cc: <stable@xxxxxxxxxxxxxxx> 3.4+
>> >> >
>> >> > ---
>> >> > drivers/pci/hotplug/pciehp_hpc.c | 9 +++++++++
>> >> > 1 file changed, 9 insertions(+)
>> >> >
>> >> > Index: linux-2.6/drivers/pci/hotplug/pciehp_hpc.c
>> >> > ===================================================================
>> >> > --- linux-2.6.orig/drivers/pci/hotplug/pciehp_hpc.c
>> >> > +++ linux-2.6/drivers/pci/hotplug/pciehp_hpc.c
>> >> > @@ -637,6 +637,15 @@ int pciehp_power_off_slot(struct slot *
>> >> > }
>> >> > ctrl_dbg(ctrl, "%s: SLOTCTRL %x write cmd %x\n", __func__,
>> >> > pci_pcie_cap(ctrl->pcie->port) + PCI_EXP_SLTCTL,
>> >> > slot_cmd);
>> >> > +
>> >> > + /*
>> >> > + * Enable link for a while so chipset could settle down
>> >> > + * inband presence detection logic
>> >> > + */
>> >> > + pciehp_link_enable(ctrl);
>> >> > + msleep(20);
>> >> > + pciehp_link_disable(ctrl);
>> >> > +
>> >> > return 0;
>> >> > }
>> >> >
>> >> --
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>> >>
>> >
>> >
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