Re: [PATCH 2/5] pciehp: Don't enable presence notification while surprise removal is not supported.

[Bjorn Helgaas <bhelgaas@google.com>]

On Wed, Jul 11, 2012 at 12:49 PM, Yinghai Lu <yinghai@kernel.org> wrote:
> On Wed, Jul 11, 2012 at 11:15 AM, Bjorn Helgaas <bhelgaas@google.com> 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.

> 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.

The attention button is optional.  What happens today when you plug a
card into a slot with no attention button?