Cold plugged bridges are not hot unpluggable, even when their hotplug
property (acpi-pci-hotplug-with-bridge-support) is turned off. Please see
the function acpi_pcihp_pc_no_hotplug(). However, with
the current implementaton, Windows would try to hot-unplug a pci bridge when
it's hotplug switch is off. This is regardless of whether there are devices
attached to the bridge. This is because we add ACPI code like _EJ0 etc for the
pci slot where the bridge is cold plugged.

In this fix, we identify a cold plugged bridge and for cold plugged bridges,
we do not add the appropriate ACPI methods that are used by the OS
to identify a hot-pluggable/unpluggable pci device. After this change, Windows
does not detect the cold plugged pci bridge as ejectable.

As a result of the patch, the following are the changes to the DSDT ACPI
table:

@@ -858,38 +858,33 @@
                     Return (Zero)
                 }

                 Method (_S2D, 0, NotSerialized)  // _S2D: S2 Device State
                 {
                     Return (Zero)
                 }

                 Method (_S3D, 0, NotSerialized)  // _S3D: S3 Device State
                 {
                     Return (Zero)
                 }
             }

             Device (S18)
             {
-                Name (_SUN, 0x03)  // _SUN: Slot User Number
                 Name (_ADR, 0x00030000)  // _ADR: Address
-                Method (_EJ0, 1, NotSerialized)  // _EJx: Eject Device
-                {
-                    PCEJ (BSEL, _SUN)
-                }
             }

             Device (S20)
             {
                 Name (_SUN, 0x04)  // _SUN: Slot User Number
                 Name (_ADR, 0x00040000)  // _ADR: Address
                 Method (_EJ0, 1, NotSerialized)  // _EJx: Eject Device
                 {
                     PCEJ (BSEL, _SUN)
                 }
             }

             Device (S28)
             {
                 Name (_SUN, 0x05)  // _SUN: Slot User Number
                 Name (_ADR, 0x00050000)  // _ADR: Address
@@ -1148,37 +1143,32 @@
                     PCEJ (BSEL, _SUN)
                 }
             }

             Device (SF8)
             {
                 Name (_SUN, 0x1F)  // _SUN: Slot User Number
                 Name (_ADR, 0x001F0000)  // _ADR: Address
                 Method (_EJ0, 1, NotSerialized)  // _EJx: Eject Device
                 {
                     PCEJ (BSEL, _SUN)
                 }
             }

             Method (DVNT, 2, NotSerialized)
             {
-                If ((Arg0 & 0x08))
-                {
-                    Notify (S18, Arg1)
-                }
-
                 If ((Arg0 & 0x10))
                 {
                     Notify (S20, Arg1)
                 }

                 If ((Arg0 & 0x20))
                 {
                     Notify (S28, Arg1)
                 }

                 If ((Arg0 & 0x40))
                 {
                     Notify (S30, Arg1)
                 }

                 If ((Arg0 & 0x80))

While at it, I have also updated a stale comment.

Signed-off-by: Ani Sinha <ani@anisinha.ca>
Suggested-by: Julia Suvorova <jusual@redhat.com>
Reviewed-by: Julia Suvorova <jusual@redhat.com>
Reviewed-by: Igor Mammedov <imammedo@redhat.com>
Message-Id: <20200918084111.15339-6-ani@anisinha.ca>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>