linux-kernel - [PATCH v4 0/3] PCI: pciehp: Do not turn off slot if presence comes up after link

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Date:   Fri, 25 Oct 2019 15:00:44 -0400
From:   Stuart Hayes <stuart.w.hayes@...il.com>
To:     Bjorn Helgaas <bhelgaas@...gle.com>
Cc:     Austin Bolen <austin_bolen@...l.com>, keith.busch@...el.com,
        Alexandru Gagniuc <mr.nuke.me@...il.com>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        "Gustavo A . R . Silva" <gustavo@...eddedor.com>,
        Sinan Kaya <okaya@...nel.org>,
        Oza Pawandeep <poza@...eaurora.org>, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org, lukas@...ner.de,
        Stuart Hayes <stuart.w.hayes@...il.com>
Subject: [PATCH v4 0/3] PCI: pciehp: Do not turn off slot if presence comes up after link

In older PCIe specs, PDS (presence detect) would come up when the
"in-band" presence detect pin connected, and would be up before DLLLA
(link active).

In PCIe 4.0 (as an ECN) and in PCIe 5.0, there is a new bit to show if
in-band presence detection can be disabled for the slot, and another bit
that disables it--and a recommendation that it should be disabled if it
can be. In addition, certain OEMs disable in-band presence detection
without implementing these bits.

This means it is possible to get a "card present" interrupt after the
link is up and the driver is loaded.  This causes an erroneous removal
of the device driver, followed by an immediate re-probing.

This patch set defines these new bits, uses them to disable in-band
presence detection if it can be, waits for PDS to go up if in-band
presence detection is disabled, and adds a DMI table that will let us
know if we should assume in-band presence is disabled on a system.

The first two patches in this set come from a patch set that was
submitted but not accepted many months ago by Alexandru Gagniuc [1].
The first is unmodified, the second has the commit message and timeout 
modified.

[1] https://patchwork.kernel.org/cover/10909167/
    [v3,0/4] PCI: pciehp: Do not turn off slot if presence comes up after link

v2:
- modify loop in pcie_wait_for_presence to do..while

v3:
- remove unused variable declaration
- modify text of warning message

v4:
- remove "!!" boolean conversion in an "if" condition for readability
- add explanation comment in dmi table

Alexandru Gagniuc (2):
  PCI: pciehp: Add support for disabling in-band presence
  PCI: pciehp: Wait for PDS if in-band presence is disabled

Stuart Hayes (1):
  PCI: pciehp: Add dmi table for in-band presence disabled

 drivers/pci/hotplug/pciehp.h     |  1 +
 drivers/pci/hotplug/pciehp_hpc.c | 50 +++++++++++++++++++++++++++++++-
 include/uapi/linux/pci_regs.h    |  2 ++
 3 files changed, 52 insertions(+), 1 deletion(-)

-- 
2.18.1