Re: [PATCH] pci/shpc: don't push attention button when ejecting powered-off device

[Roman Kagan <rvkagan@yandex-team.ru>]

On Mon, Nov 02, 2020 at 08:37:50AM +0300, Roman Kagan wrote:
> When the slot is in steady powered-off state and the device is being
> removed, there's no need to press the attention button.  Nor is it
> mandated by the Standard Hot-Plug Controller Specification, Rev. 1.0.
> 
> Moreover it confuses the guest, Linux in particular, as it assumes that
> the attention button pressed in this state indicates that the device has
> been inserted and will need to be powered on.  Therefore it transitions
> the slot into BLINKING_ON state for 5 seconds, and discovers at the end
> that no device is actually inserted:
> 
> ... unplug request
> [12685.451329] shpchp 0000:01:00.0: Button pressed on Slot(2)
> [12685.455478] shpchp 0000:01:00.0: PCI slot #2 - powering off due to button press
> ... in 5 seconds OS powers off the slot, QEMU ejects the device
> [12690.632282] shpchp 0000:01:00.0: Latch open on Slot(2)
> ... excessive button press in steady powered-off state
> [12690.634267] shpchp 0000:01:00.0: Button pressed on Slot(2)
> [12690.636256] shpchp 0000:01:00.0: Card not present on Slot(2)
> ... the last button press spawns powering on the slot
> [12690.638909] shpchp 0000:01:00.0: PCI slot #2 - powering on due to button press
> ... in 5 more seconds attempt to power on discovers empty slot
> [12695.735986] shpchp 0000:01:00.0: No adapter on slot(2)
> 
> Worse, if the real device insertion happens within 5 seconds from the
> apparent completion of the previous device removal (signaled via
> DEVICE_DELETED event), the new button press will be interpreted as the
> cancellation of that misguided powering on:
> 
> [13448.965295] shpchp 0000:01:00.0: Button pressed on Slot(2)
> [13448.969430] shpchp 0000:01:00.0: PCI slot #2 - powering off due to button press
> [13454.025107] shpchp 0000:01:00.0: Latch open on Slot(2)
> [13454.027101] shpchp 0000:01:00.0: Button pressed on Slot(2)
> [13454.029165] shpchp 0000:01:00.0: Card not present on Slot(2)
> ... the excessive button press spawns powering on the slot
> ... device has already been ejected by QEMU
> [13454.031949] shpchp 0000:01:00.0: PCI slot #2 - powering on due to button press
> ... new device is inserted in the slot
> [13456.861545] shpchp 0000:01:00.0: Latch close on Slot(2)
> ... valid button press arrives before 5 s since the wrong one
> [13456.864894] shpchp 0000:01:00.0: Button pressed on Slot(2)
> [13456.869211] shpchp 0000:01:00.0: Card present on Slot(2)
> ... the valid button press is counted as cancellation of the wrong one
> [13456.873173] shpchp 0000:01:00.0: Button cancel on Slot(2)
> [13456.877101] shpchp 0000:01:00.0: PCI slot #2 - action canceled due to button press
> 
> As a result, the newly inserted device isn't brought up by the guest.
> 
> Avoid this situation by not pushing the attention button when the device
> in the slot is in powered-off state and is being ejected.
> 
> FWIW pcie implementation doesn't suffer from this problem.
> 
> Signed-off-by: Roman Kagan <rvkagan@yandex-team.ru>
> ---
>  hw/pci/shpc.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/hw/pci/shpc.c b/hw/pci/shpc.c
> index b00dce629c..837159c5bd 100644
> --- a/hw/pci/shpc.c
> +++ b/hw/pci/shpc.c
> @@ -300,7 +300,6 @@ static void shpc_slot_command(SHPCDevice *shpc, uint8_t target,
>              shpc_set_status(shpc, slot, SHPC_SLOT_STATUS_PRSNT_EMPTY,
>                              SHPC_SLOT_STATUS_PRSNT_MASK);
>              shpc->config[SHPC_SLOT_EVENT_LATCH(slot)] |=
> -                SHPC_SLOT_EVENT_BUTTON |
>                  SHPC_SLOT_EVENT_MRL |
>                  SHPC_SLOT_EVENT_PRESENCE;
>          }
> @@ -566,7 +565,6 @@ void shpc_device_unplug_request_cb(HotplugHandler *hotplug_dev,
>          return;
>      }
>  
> -    shpc->config[SHPC_SLOT_EVENT_LATCH(slot)] |= SHPC_SLOT_EVENT_BUTTON;
>      state = shpc_get_status(shpc, slot, SHPC_SLOT_STATE_MASK);
>      led = shpc_get_status(shpc, slot, SHPC_SLOT_PWR_LED_MASK);
>      if (state == SHPC_STATE_DISABLED && led == SHPC_LED_OFF) {
> @@ -577,6 +575,8 @@ void shpc_device_unplug_request_cb(HotplugHandler *hotplug_dev,
>          shpc->config[SHPC_SLOT_EVENT_LATCH(slot)] |=
>              SHPC_SLOT_EVENT_MRL |
>              SHPC_SLOT_EVENT_PRESENCE;
> +    } else {
> +        shpc->config[SHPC_SLOT_EVENT_LATCH(slot)] |= SHPC_SLOT_EVENT_BUTTON;
>      }
>      shpc_set_status(shpc, slot, 0, SHPC_SLOT_STATUS_66);
>      shpc_interrupt_update(pci_hotplug_dev);
> -- 
> 2.28.0
> 

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