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    SubjectRe: [PATCH v2 0/8] PCI: Improvements for native PCIe hotplug
    On Fri, Oct 13, 2017 at 09:35:40PM +0300, Mika Westerberg wrote:
    > Currently when plugging PCIe device using native PCIe hotplug Linux PCI
    > core tries to allocate bus space and resources so that the newly enumerated
    > topology barely fits there. Now, if the PCIe topology that was just plugged
    > in has more PCIe hotplug ports we will run out of bus space and resources
    > pretty quickly. There is a workaround for this by passing pci=hpbussize=N
    > in the kernel command line but it runs to the same situation after next
    > hotplug.
    >
    > A good example where this is a problem is Thunderbolt where each
    > Thunderbolt device includes PCIe switch and the topology can be extended up
    > to 6 chained devices.
    >
    > Future platforms will move from BIOS assisted (ACPI) hotplug from native
    > PCIe hotplug because then it is possible to power down PCIe hotplug ports
    > without confusing the SMI handler which is not necessary when native PCIe
    > hotplug is used. Also Apple Macs have been using native PCIe hotplug from
    > the beginning. Windows already knows how to handle these complex PCIe
    > topologies and we will reuse the same knowledge in Linux with this patch
    > series.
    >
    > The idea is to distribute available bus space and resources to hotplug PCIe
    > downstream ports so that the PCIe chain can be extended from those points.
    > The initial available space is configured by the BIOS to the root port in
    > question.
    >
    > This series first teaches the Linux PCI core to distribute available bus
    > space and resources if PCIe hotplug is used. Then following are fixes for
    > issues found while testing.
    >
    > With this series applied I can connect the maximum length Thunderbolt PCIe
    > chain (6 devices) to a Macbook Pro as can be seen from the 'lspci -t'
    > output below:
    >
    > -[0000:00]-+-00.0
    > +-02.0
    > +-14.0
    > +-16.0
    > +-19.0
    > +-1c.0-[01]----00.0
    > +-1c.4-[03-78]----00.0-[04-78]--+-00.0-[05]----00.0
    > | +-01.0-[07-3f]----00.0-[08-3f]--+-01.0-[09]----00.0
    > | | \-04.0-[0a-3f]----00.0-[0b-3f]--+-01.0-[0c]----00.0
    > | | \-04.0-[0d-3f]----00.0-[0e-3f]--+-01.0-[0f]--
    > | | \-04.0-[10-3f]----00.0-[11-3f]--+-01.0-[12]----00.0
    > | | \-04.0-[13-3f]----00.0-[14-3f]--+-01.0-[15]----00.0
    > | | \-04.0-[16-3f]----00.0-[17-3f]----00.0-[18-3f]----00.0
    > | +-02.0-[06]----00.0
    > | \-04.0-[40-78]--
    > +-1d.0-[79-ee]----00.0-[7a-ee]--+-00.0-[7b]----00.0
    > | +-01.0-[7d-b5]--
    > | +-02.0-[7c]----00.0
    > | \-04.0-[b6-ee]--
    > +-1d.3-[02]----00.0
    > +-1e.0
    > +-1e.1
    > +-1e.3
    > +-1f.0
    > +-1f.2
    > +-1f.3
    > \-1f.4
    >
    > The previous version (v1) of the patch series can be found here:
    >
    > https://www.spinics.net/lists/linux-pci/msg64841.html
    >
    > Changes from v1:
    >
    > * Rebase on top of Andy's for_each_pci_bridge() patch
    > * Move pci_hp_add_bridge() to drivers/pci/probe.c
    > * Split open-coding of the two pass scan loop into a separate patch
    > * Drop [PATCH 2/7] PCI: Introduce pcie_upstream_port()
    > * Keep pci_scan_bridge_extend() and pci_scan_child_bus_extend() internal
    > to drivers/pci/probe.c
    > * Add another separate loop to count number of hotplug and normal bridges
    > * Reword comment about two scans
    > * Generalize patches 4 and 5 so that they could work also on conventional
    > PCI by dropping tests for PCIe.
    >
    > Mika Westerberg (8):
    > PCI: Move pci_hp_add_bridge() to drivers/pci/probe.c
    > PCI: Open-code the two pass loop when scanning bridges
    > PCI: Do not allocate more buses than available in parent
    > PCI: Distribute available buses to hotplug capable bridges
    > PCI: Distribute available resources to hotplug capable bridges
    > PCI: pciehp: Fix race condition handling surprise link down
    > PCI: pciehp: Do not clear Presence Detect Changed during initialization
    > PCI: pciehp: Check that the device is really present before touching it
    >
    > drivers/pci/Makefile | 3 -
    > drivers/pci/hotplug-pci.c | 29 ------
    > drivers/pci/hotplug/pciehp_ctrl.c | 7 +-
    > drivers/pci/hotplug/pciehp_hpc.c | 13 ++-
    > drivers/pci/hotplug/pciehp_pci.c | 18 +++-
    > drivers/pci/probe.c | 188 +++++++++++++++++++++++++++++++++++---
    > drivers/pci/setup-bus.c | 177 +++++++++++++++++++++++++++++++++++
    > 7 files changed, 379 insertions(+), 56 deletions(-)
    > delete mode 100644 drivers/pci/hotplug-pci.c

    Looks very nice!

    I applied all but the last patch ("Check that the device is really
    present") on pci/hotplug for v4.15, thanks!

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