Re: [Qemu-devel] [PATCH 3/3] hw/pcie: better hotplug/hotunplug support

["Michael S. Tsirkin" <mst@redhat.com>]

On Sun, Jun 22, 2014 at 02:11:05PM +0300, Marcel Apfelbaum wrote:
> On Sun, 2014-06-22 at 14:03 +0300, Michael S. Tsirkin wrote:
> > On Sun, Jun 22, 2014 at 01:54:06PM +0300, Marcel Apfelbaum wrote:
> > > On Thu, 2014-06-19 at 17:43 +0300, Michael S. Tsirkin wrote:
> > > > On Thu, Jun 19, 2014 at 04:52:21PM +0300, Marcel Apfelbaum wrote:
> > > > > Hotplug triggers both 'present detect change' and
> > > > > 'attention button pressed'.
> > > > > 
> > > > > Hotunplug starts by triggering 'attention button pressed',
> > > > > then waits for the OS to power off the device and only
> > > > > then detaches it.
> > > > > 
> > > > 
> > > > Pls not here that current code is broken: it does surprise removal which
> > > > crashes guests.
> > > I'll add a note, sure.
> > > 
> > > > 
> > > > > Signed-off-by: Marcel Apfelbaum <marcel.a@redhat.com>
> > > > > ---
> > > > >  hw/pci/pcie.c | 20 +++++++++++++++-----
> > > > >  1 file changed, 15 insertions(+), 5 deletions(-)
> > > > > 
> > > > > diff --git a/hw/pci/pcie.c b/hw/pci/pcie.c
> > > > > index f8bf515..9cfd93d 100644
> > > > > --- a/hw/pci/pcie.c
> > > > > +++ b/hw/pci/pcie.c
> > > > > @@ -258,7 +258,8 @@ void pcie_cap_slot_hotplug_cb(HotplugHandler *hotplug_dev, DeviceState *dev,
> > > > >  
> > > > >      pci_word_test_and_set_mask(exp_cap + PCI_EXP_SLTSTA,
> > > > >                                 PCI_EXP_SLTSTA_PDS);
> > > > > -    pcie_cap_slot_event(PCI_DEVICE(hotplug_dev), PCI_EXP_HP_EV_PDC);
> > > > > +    pcie_cap_slot_event(PCI_DEVICE(hotplug_dev),
> > > > > +                        PCI_EXP_HP_EV_PDC | PCI_EXP_HP_EV_ABP);
> > > > >  }
> > > > >  
> > > > >  void pcie_cap_slot_hot_unplug_cb(HotplugHandler *hotplug_dev, DeviceState *dev,
> > > > > @@ -268,10 +269,7 @@ void pcie_cap_slot_hot_unplug_cb(HotplugHandler *hotplug_dev, DeviceState *dev,
> > > > >  
> > > > >      pcie_cap_slot_hotplug_common(PCI_DEVICE(hotplug_dev), dev, &exp_cap, errp);
> > > > >  
> > > > > -    object_unparent(OBJECT(dev));
> > > > > -    pci_word_test_and_clear_mask(exp_cap + PCI_EXP_SLTSTA,
> > > > > -                                 PCI_EXP_SLTSTA_PDS);
> > > > > -    pcie_cap_slot_event(PCI_DEVICE(hotplug_dev), PCI_EXP_HP_EV_PDC);
> > > > > +    pcie_cap_slot_push_attention_button(PCI_DEVICE(hotplug_dev));
> > > > >  }
> > > > >  
> > > > >  /* pci express slot for pci express root/downstream port
> > > > > @@ -389,6 +387,18 @@ void pcie_cap_slot_write_config(PCIDevice *dev,
> > > > >                          sltsta);
> > > > >      }
> > > > >  
> > > > 
> > > > pls add code comments explaining the logic here.
> > > I thought is clear :(
> > > Basically: If the device is present, power indicator off and power
> > > controller off, it is safe to detach the device.
> > 
> > Sure, put this in the comment.
> > 
> > > > 
> > > > > +    if ((sltsta & PCI_EXP_SLTSTA_PDS) && (val & PCI_EXP_SLTCTL_PCC) &&
> > > > > +        ((val & PCI_EXP_SLTCTL_PIC_OFF) == PCI_EXP_SLTCTL_PIC_OFF)) {
> > > > > +        PCIDevice *slot_dev = pci_bridge_get_sec_bus(PCI_BRIDGE(dev))->devices[0];
> > > > > +        if (slot_dev) {
> > > > 
> > > > Here you want to remove all devices behind the bridge?
> > > Yes, but since it is PCIe we only have one device,
> > > but we may have a multi-function device...
> > 
> > Exactly. Up to 256 functions.
> > 
> > > > You need to do this for all functions, not just function 0.
> > > So bus devices are actually functions... OK, I'll run a loop here.
> > > 
> > > > 
> > > > > +            object_unparent(OBJECT(slot_dev));
> > > > > +            pci_word_test_and_clear_mask(exp_cap + PCI_EXP_SLTSTA,
> > > > > +                                         PCI_EXP_SLTSTA_PDS);
> > > > > +            pci_word_test_and_set_mask(exp_cap + PCI_EXP_SLTSTA,
> > > > > +                                       PCI_EXP_SLTSTA_PDC);
> > > > 
> > > > These bits need to be cleared in any case?
> > > No, "PDS on" means the devices is present, so we clear it only after the
> > > OS  powers it off.
> > 
> > So why not clear PDS unconditionally?
> Because we are 'allowed' to remove the device only when the OS tells us
> the power is off. Before that, it can result in data loss,
> since the device driver is not yet unloaded.

Yes. But if (slot_dev) seems not to be needed:
if slot is empty we can clear PDC.



> 
> > > > 
> > > > > +        }
> > > > > +    }
> > > > > +
> > > > >      hotplug_event_notify(dev);
> > > > >  
> > > > >      /* 
> > > > > -- 
> > > > > 1.8.3.1
> > > 
> > > 
> 
>