If a PCIe hotplug slot has an Attention Button, the normal hot-add flow is:

  - Slot is empty and slot power is off
  - User inserts card in slot and presses Attention Button
  - OS blinks Power Indicator for 5 seconds
  - After 5 seconds, OS turns on Power Indicator, turns on slot power, and
    enumerates the device

Previously, if a user pressed the Attention Button on an *empty* slot,
pciehp logged the following messages and blinked the Power Indicator
until a second button press:

  [0.000] pciehp: Button press: will power on in 5 sec
  [0.001] # Power Indicator starts blinking
  [5.001] # 5 second timeout; slot is empty, so we should cancel the
            request to power on and turn off Power Indicator

  [7.000] # Power Indicator still blinking
  [8.000] # possible card insertion
  [9.000] pciehp: Button press: canceling request to power on

The first button press incorrectly left the slot in BLINKINGON_STATE, so
the second was interpreted as a "cancel power on" event regardless of
whether a card was present.

If the slot is empty, turn off the Power Indicator and return from
BLINKINGON_STATE to OFF_STATE after 5 seconds, effectively canceling the
request to power on.  Putting the slot in OFF_STATE also means the second
button press will correctly request a slot power on if the slot is
occupied.

[bhelgaas: commit log]
Link: https://lore.kernel.org/r/20230512021518.336460-1-clementwei90@163.com
Fixes: d331710e ("PCI: pciehp: Become resilient to missed events")
Suggested-by: Lukas Wunner <lukas@wunner.de>
Signed-off-by: Rongguang Wei <weirongguang@kylinos.cn>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Lukas Wunner <lukas@wunner.de>