On Wed, Jul 11, 2012 at 2:28 PM, Yinghai Lu <yinghai@xxxxxxxxxx> wrote: > On Wed, Jul 11, 2012 at 12:56 PM, Bjorn Helgaas <bhelgaas@xxxxxxxxxx> wrote: >> On Wed, Jul 11, 2012 at 12:49 PM, Yinghai Lu <yinghai@xxxxxxxxxx> wrote: >>> On Wed, Jul 11, 2012 at 11:15 AM, Bjorn Helgaas <bhelgaas@xxxxxxxxxx> wrote: >>>> >>>> What's the connection with HP_SUPR_RM()? Is it just a coincidence >>>> that chipsets that set the "Hot-Plug Surprise" bit don't have this >>>> problem with the Presence Detect State bit? >>>> >>>> Using HP_SUPR_RM() seems like a totally bogus way to work around a >>>> presence detect issue. >>> >>> then we should blame the spec. >> >> What specifically are you referring to? I see this Presence Detect State text: >> >> 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. Note that the in-band presence >> detect mechanism requires that power be applied to an adapter >> for its presence to be detected. Consequently, form factors that >> require a power controller for hot-plug must implement a >> physical pin presence detect mechanism. >> >> But I don't yet see the connection with the Hot-Plug Surprise bit. > > Spec does not mention about surprise add clearly. No, in fact the Hot-Plug Surprise description mentions *removal* twice and doesn't mention *add* at all. >>> and if you do the above changing, when plug the card into system, >>> kernel will bring that card online automatically without press >>> attention button. >>> that will be big change. >> >> I don't want to make a fundamental change in behavior like that. I'm >> just trying to understand why we should handle Presence Detect >> differently based on the Hot-Plug Surprise bit. > > When hotplug surprise is supported, attention button may not there. > So have to use present bit to trigger the sequence online work, and > offline clean up work. Well, there is an "Attention Button Present" bit. Why wouldn't we use that instead of trying to infer the button's presence from Hot-Plug Surprise? > When hotplug surprise is not there, why should we handle Presence Bit change? > >> >> The attention button is optional. What happens today when you plug a >> card into a slot with no attention button? > if the slot support hotplug surprise, that card will be online automatically. > if the slot does not support hotplug surprise, but that slot have > power control, then could use need sw interface /sys/..../power to > turn on the power and bring that card online. > > > Yinghai -- 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
