On Wed, Apr 10, 2013 at 10:34 AM, Takashi Iwai <tiwai@xxxxxxx> wrote: > Hi Bjorn, > > sorry for the late follow up as I was on vacation and has been busy > for other tasks. Since this topic went to nirvana, I try to whip > again... > > At Mon, 25 Mar 2013 10:58:40 -0600, > Bjorn Helgaas wrote: >> >> On Wed, Mar 20, 2013 at 8:02 AM, Takashi Iwai <tiwai@xxxxxxx> wrote: >> > We encountered a problem that on some HP machines the Realtek PCI-e >> > card reader device appears only when you inserted a card before the >> > cold boot. While debugging, it turned out that the device is actually >> > handled via PCI-e hotplug in some level. The device sends a presence >> > change notification, and pciehp receives it, but it's ignored because >> > of lack of the hotplug surprise (PCI_EXP_SLTCAP_HPS) capability bit. >> > Once when this check passes, everything starts working -- the device >> > appears upon plugging the card properly. >> > >> > There are a few other bug reports indicating the similar problems >> > (e.g. on recent Dell laptops), and I guess the culprit is same. >> >> Can you point us at these bug reports, e.g., with URLs? Hopefully >> they will contain complete dmesg logs and "lspci -vv" outputs so we >> can debug this a bit more. > > The machine isn't in market yet, so we cannot expose all things, but I > attach the lspci snippet of the relevant parts, pci-e ports and the > card reader, at least. If you need anything else, let me know. > > As Oliver and Michal already replied, Windows (both 7/8) identifies > the device without modification. This implies that Windows handles > the hotplug no matter whether the surprise bit is set or not, either > globally or device-specifically. But, since this is pretty new > hardware, we highly doubt it's done in a white-list basis. > >> I'm strongly opposed to adding a module option to work around this >> issue because the user experience is unacceptable. We can't expect >> users to debug the problem and discover the option. >> >> I'm also opposed to a DMI quirk system because I think it's very >> likely that this device works correctly under Windows, and I doubt >> very much that Windows has to include the equivalent of DMI quirks. >> So we should, at least in principle, be able to figure out how to make >> it work, too. > > In order to get things a bit straight, let me list up the things we > found again: > > - The Realtek card reader devices doesn't appear in lspci at the > fresh boot in multiple kernel versions from 3.0 to 3.9. > > - Once when the card is inserted, it issues the hotplug IRQ event. > > - pciehp receives and handles the event but it doesn't add/remove the > device actually because the corresponding controller has no surprise > bit. > > When forcibly enabling the hotplug device addition by my patch, it > starts working. The device is added at card insert. The removal > doesn't trigger on our system, but the event itself seems > generated. > > - The surprise bit can't be changed as it's supposed to be read-only > register bits. Thus no PCI quirk seems possible, and it has to be > fixed in pciehp. > > - Another way to detect the PCI card reader device is to perform > echo 1 > /sys/bus/pci/rescan > with a memory card inserted. It doesn't work without the card, > and it is less sophisticated than pciehp, of course. > > Right now, we applied a patch for pciehp to ignore the surprise bit > per basis of DMI string match. This works, but doesn't scale; if the > same problem happens on a similar model, the driver must be compiled > again. A module option would be really convenient for that, although > I understand your concern, too. > > Of course, an alternative (and more radical) solution is to remove the > surprise bit check completely from pciehp, as Matthew suggested in the > thread. What risk would it bring? I think we need to ignore the surprise bit as Matthew suggested. Alex raised an issue with this (secondary bus reset causes a device remove followed by device add), so we'd have to work through that somehow. I think doing the remove/add would actually be more correct because we would be doing the whole device initialization after the reset. We currently save/restore some device state around the reset, but that's a piecemeal approach that is certain to miss internal hidden state. But I don't know how to deal with the KVM implications of remove/add. Bjorn -- 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
