Re: [Qemu-devel] [PATCH 2/5] acpi_piix4: Only allow writes to PCI hotplug eject register

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

On Thu, Apr 05, 2012 at 10:21:18AM +0200, Igor Mammedov wrote:
> On 04/05/2012 07:51 AM, Alex Williamson wrote:
> >This is never read.  We can also derive bus from the write handler,
> >making this more inline with the other callbacks.  Note that
> >pciej_write was actually called with (PCIBus *)dev->bus, which is
> >cast as a void* allowing us to pretend it's a BusState*.  Fix this
> >so we don't depend on the BusState location within PCIBus.
> >
> >Signed-off-by: Alex Williamson<alex.williamson@redhat.com>
> >---
> >
> >  docs/specs/acpi_pci_hotplug.txt |    2 +-
> >  hw/acpi_piix4.c                 |   14 ++++----------
> >  2 files changed, 5 insertions(+), 11 deletions(-)
> >
> >diff --git a/docs/specs/acpi_pci_hotplug.txt b/docs/specs/acpi_pci_hotplug.txt
> >index 1e2c8a2..1e61d19 100644
> >--- a/docs/specs/acpi_pci_hotplug.txt
> >+++ b/docs/specs/acpi_pci_hotplug.txt
> >@@ -28,7 +28,7 @@ PCI device eject (IO port 0xae08-0xae0b, 4-byte access):
> >  ----------------------------------------
> >
> >  Used by ACPI BIOS _EJ0 method to request device removal. One bit per slot.
> >-Reads return 0.
> >+Read-only.
> Write-only perhaps?

Yes, let's also specify what happens in practice.
I think it is 'Guest should never read this register, in practice
0 is returned'.

> >
> >  PCI removability status (IO port 0xae0c-0xae0f, 4-byte access):
> >  -----------------------------------------------
> >diff --git a/hw/acpi_piix4.c b/hw/acpi_piix4.c
> >index 44d1423..6ee832a 100644
> >--- a/hw/acpi_piix4.c
> >+++ b/hw/acpi_piix4.c
> >@@ -487,15 +487,11 @@ static uint32_t pci_down_read(void *opaque, uint32_t addr)
> >      return val;
> >  }
> >
> >-static uint32_t pciej_read(void *opaque, uint32_t addr)
> >-{
> >-    PIIX4_DPRINTF("pciej read %x\n", addr);
> >-    return 0;
> >-}
> >-
> what will happen if bios tries to read from reg?

I think it currently gets 0.

> >  static void pciej_write(void *opaque, uint32_t addr, uint32_t val)
> >  {
> >-    BusState *bus = opaque;
> >+    PIIX4PMState *s = opaque;
> >+    PCIDevice *dev =&s->dev;
> >+    BusState *bus = qdev_get_parent_bus(&dev->qdev);
> >      DeviceState *qdev, *next;
> >      int slot = ffs(val) - 1;
> >
> >@@ -507,7 +503,6 @@ static void pciej_write(void *opaque, uint32_t addr, uint32_t val)
> >          }
> >      }
> >
> >-
> >      PIIX4_DPRINTF("pciej write %x<== %d\n", addr, val);
> >  }
> >
> >@@ -547,8 +542,7 @@ static void piix4_acpi_system_hot_add_init(PCIBus *bus, PIIX4PMState *s)
> >      register_ioport_read(PCI_UP_BASE, 4, 4, pci_up_read, s);
> >      register_ioport_read(PCI_DOWN_BASE, 4, 4, pci_down_read, s);
> >
> >-    register_ioport_write(PCI_EJ_BASE, 4, 4, pciej_write, bus);
> >-    register_ioport_read(PCI_EJ_BASE, 4, 4,  pciej_read, bus);
> >+    register_ioport_write(PCI_EJ_BASE, 4, 4, pciej_write, s);
> >
> >      register_ioport_write(PCI_RMV_BASE, 4, 4, pcirmv_write, s);
> >      register_ioport_read(PCI_RMV_BASE, 4, 4,  pcirmv_read, s);
> >
> 
> -- 
> -----
>  Igor