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Date: Sat, 31 Mar 2018 13:37:23 +0300
From: Mika Westerberg <mika.westerberg@linux.intel.com>
To: Lukas Wunner <lukas@wunner.de>
Cc: Bjorn Helgaas <helgaas@kernel.org>, Bjorn Helgaas <bhelgaas@google.com>,
	"Rafael J. Wysocki" <rjw@rjwysocki.net>,
	Len Brown <lenb@kernel.org>, Mario.Limonciello@dell.com,
	Michael Jamet <michael.jamet@intel.com>,
	Yehezkel Bernat <yehezkel.bernat@intel.com>,
	Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
	linux-pci@vger.kernel.org, linux-acpi@vger.kernel.org
Subject: Re: [PATCH v3 1/5] PCI: Make sure all bridges reserve at least one
 bus number
Message-ID: <20180331103723.GX2703@lahna.fi.intel.com>
References: <20180328114346.GZ2703@lahna.fi.intel.com>
 <20180328180906.GI7759@bhelgaas-glaptop.roam.corp.google.com>
 <20180329115911.GN2703@lahna.fi.intel.com>
 <20180331082903.GA21051@wunner.de>
 <20180331085852.GQ2703@lahna.fi.intel.com>
 <20180331091245.GA10720@wunner.de>
 <20180331092017.GS2703@lahna.fi.intel.com>
 <20180331093017.GB10720@wunner.de>
 <20180331095804.GU2703@lahna.fi.intel.com>
 <20180331101816.GA18877@wunner.de>
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In-Reply-To: <20180331101816.GA18877@wunner.de>
List-ID: <linux-pci.vger.kernel.org>

On Sat, Mar 31, 2018 at 12:18:16PM +0200, Lukas Wunner wrote:
> On Sat, Mar 31, 2018 at 12:58:04PM +0300, Mika Westerberg wrote:
> > On Sat, Mar 31, 2018 at 11:30:17AM +0200, Lukas Wunner wrote:
> > > > The whole point here is that those are *not* hotplug slots just regular
> > > > downstream ports.
> > > 
> > > Okay, understood.  Is this about the NHI or XHCI?  Because at least
> > > on Alpine Ridge (C step), the bridge above the XHCI *is* a hotplug
> > > bridge.  Only the bridge above the NHI is not.
> > 
> > Yes, exactly. I tried to clarify this mechanism a bit better in the
> > other email I just sent.
> 
> But in the e-mail you just sent, the bridge above the XHCI is not a
> hotplug bridge and according to the lspci output of a MacBookPro13,3
> I have here, it *is* a hotplug bridge on Alpine Ridge (C step).

They are different because on Apple systems the Thunderbolt host router
(switch + xHCI + NHI) are always there and thus configured by the boot
firmware initially. So there is no need for this ACPI Notify() mechanism
at all, so the downstream port leading to xHCI can be marked as
hotplug capable (even though not needed actually).

The systems I'm refering are in "native" mode which means that they use
native PCIe hotplug also for the Thunderbolt host router and thus it is
up to the OS to configure everything. The reason those two ports are not
marked as hotplug is that then the OS does not try to distribute all
remaining resources to them which leaves more space to the extension
hotplug port.