From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-lb0-f174.google.com ([209.85.217.174]:43340 "EHLO mail-lb0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932444Ab2GKT5Q convert rfc822-to-8bit (ORCPT ); Wed, 11 Jul 2012 15:57:16 -0400 Received: by lbbgm6 with SMTP id gm6so2921965lbb.19 for ; Wed, 11 Jul 2012 12:57:15 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: References: <1340437325-29282-1-git-send-email-yinghai@kernel.org> <1340437325-29282-3-git-send-email-yinghai@kernel.org> <20120711162120.GA17988@google.com> From: Bjorn Helgaas Date: Wed, 11 Jul 2012 13:56:55 -0600 Message-ID: Subject: Re: [PATCH 2/5] pciehp: Don't enable presence notification while surprise removal is not supported. To: Yinghai Lu Cc: linux-pci@vger.kernel.org, Kenji Kaneshige Content-Type: text/plain; charset=windows-1252 Sender: linux-pci-owner@vger.kernel.org List-ID: On Wed, Jul 11, 2012 at 12:49 PM, Yinghai Lu wrote: > On Wed, Jul 11, 2012 at 11:15 AM, Bjorn Helgaas 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?