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 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 | 45 +++++++++++++++++++++++++++++++- include/uapi/linux/pci_regs.h | 2 ++ 3 files changed, 47 insertions(+), 1 deletion(-) -- 2.18.1
