Hello, > -----Original Message----- > From: Ethan Zhao [mailto:ethan.kernel@xxxxxxxxx] > Sent: Monday, December 09, 2013 8:08 PM > To: Rajat Jain > Cc: Bjorn Helgaas; Yinghai Lu; linux-pci@xxxxxxxxxxxxxxx; Kenji > Kaneshige; stable@xxxxxxxxxxxxxxx; Guenter Roeck > Subject: Re: [PATCH] PCI, pciehp: Turn on link a while to workaround > presense detection > > Rajat, > After read almost all the proposed material you mentioned, Thanks a bunch for putting in efforts, I appreciate. > 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. Yes. That is what I had based my patch on. > > 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. I totally agree. My proposal was to add link state event * in addition to * other already existing mechanisms. That should (atleast in principle) not disturb existing mechanisms. In fact, originally I proposed introducing a module parameter for enabling use of link events for hotplug. But later after discussion with Bjorn, I changed it to always enable. > 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. Yes, I understand. In fact I had discussed with Bjorn how the behavior might change and atleast my impression was that he seemed to be okay with it: http://marc.info/?t=138513966800006&r=1&w=2 > > 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. Sure, I understand and would fully comply. I'm have reasonable level of confidence that my patch addresses a problem that is Faced by many products that do not support traditional HP elements. Thus to that Extent, I wanted my work to be useful to the community. As far as I could think of, I had submitted my patch with the hope that some one will take a look and point out any foreseen Issues, but unfortunately could not get a lot of attention. Not sure what should be the next step :-( Actually the reason I spoke up in this thread was that I wanted to make aware that I am proposing that the link not be permanently left disabled at the time of power off, and discuss any related issues thereof. Thanks & best Regards, Rajat > > 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; > >> >> > } > >> >> > > >> >> -- > >> >> To unsubscribe from this list: send the line "unsubscribe linux- > pci" > >> >> in the body of a message to majordomo@xxxxxxxxxxxxxxx More > >> >> majordomo info at http://vger.kernel.org/majordomo-info.html > >> >> > >> > > >> > > >> > -- > >> > To unsubscribe from this list: send the line "unsubscribe linux- > pci" > >> > in the body of a message to majordomo@xxxxxxxxxxxxxxx More > >> > majordomo info at http://vger.kernel.org/majordomo-info.html > >> -- > >> To unsubscribe from this list: send the line "unsubscribe linux-pci" > >> in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo > >> info at http://vger.kernel.org/majordomo-info.html > >> > > > > > -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
