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When acpiphp re-enumerates a PCI hierarchy because of an ACPI Notify()
event, we should skip bridges managed by native hotplug (pciehp or shpchp).
We don't want to scan below a native hotplug bridge until the hotplug
controller generates a hot-add event.
A typical scenario is a Root Port leading to a Thunderbolt host router that
remains powered off until something is connected to it. See [1] for the
lspci details.
1. Before something is connected, only the Root Port exists. It has
PCI_EXP_SLTCAP_HPC set and pciehp is responsible for hotplug:
00:1b.0 Root Port (HotPlug+)
2. When a USB-C or Thunderbolt device is connected, the Switch in the
Thunderbolt host router is powered up, the Root Port signals a hotplug
add event and pciehp enumerates the Switch:
01:00.0 Switch Upstream Port to [bus 02-39]
02:00.0 Switch Downstream Port to [bus 03] (HotPlug-, to NHI)
02:01.0 Switch Downstream Port to [bus 04-38] (HotPlug+, to Thunderbolt connector)
02:02.0 Switch Downstream Port to [bus 39] (HotPlug-, to xHCI)
The 02:00.0 and 02:02.0 Ports lead to Endpoints that are not powered
up yet. The Ports have PCI_EXP_SLTCAP_HPC cleared, so pciehp doesn't
handle hotplug for them and we assign minimal resources to them.
The 02:01.0 Port has PCI_EXP_SLTCAP_HPC set, so pciehp handles native
hotplug events for it.
3. The BIOS powers up the xHCI controller. If a Thunderbolt device was
connected (not just a USB-C device), it also powers up the NHI. Then
it sends an ACPI Notify() to the Root Port, and acpiphp enumerates the
new device(s):
03:00.0 Thunderbolt Host Controller (NHI) Endpoint
39:00.0 xHCI Endpoint
4. If a Thunderbolt device was connected, the host router firmware uses
the NHI to set up Thunderbolt tunnels and triggers a native hotplug
event (via 02:01.0 in this example). Then pciehp enumerates the new
Thunderbolt devices:
04:00.0 Switch Upstream Port to [bus 05-38]
05:01.0 Switch Downstream Port to [bus 06-09] (HotPlug-)
05:04.0 Switch Downstream Port to [bus 0a-38] (HotPlug+)
In this example, 05:01.0 leads to another Switch and some NICs. This
subtree is static, so 05:01.0 doesn't support hotplug and has
PCI_EXP_SLTCAP_HPC cleared.
In step 3, acpiphp previously enumerated everything below the Root Port,
including things below the 02:01.0 Port. We don't want that because pciehp
expects to manage hotplug below that Port, and firmware on the host router
may be in the middle of configuring its Link so it may not be ready yet.
To make this work better with the native PCIe (pciehp) and standard PCI
(shpchp) hotplug drivers, we let them handle all slot management and
resource allocation for hotplug bridges and restrict ACPI hotplug to
non-hotplug bridges.
[1] https://bugzilla.kernel.org/show_bug.cgi?id=199581#c5
Link: https://lkml.kernel.org/r/20180529160155.1738-1-mika.westerberg@linux.intel.com
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
[bhelgaas: changelog, use hotplug_is_native() instead of
dev->is_hotplug_bridge]
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
See Documentation/00-INDEX for a list of what is contained in each file.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.