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 <[email protected]> > --- > 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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