[PATCH v2] hw/ide/piix: properly initialize the BMIBA register

[Olaf Hering]

According to the 82371FB documentation (82371FB.pdf, 2.3.9. BMIBA—BUS
MASTER INTERFACE BASE ADDRESS REGISTER, April 1997), the register is
32bit wide. To properly reset it to default values, all 32bit need to be
cleared. Bit #0 "Resource Type Indicator (RTE)" needs to be enabled.

The initial change wrote just the lower 8 bit, leaving parts of the "Bus
Master Interface Base Address" address at bit 15:4 unchanged.

This bug went unnoticed until commit ee358e919e38 ("hw/ide/piix: Convert
reset handler to DeviceReset"). After this change, piix_ide_reset is
exercised after the "unplug" command from a Xen HVM domU, which was not
the case prior that commit. This function resets the command register.
As a result the ata_piix driver inside the domU will see a disabled PCI
device. The generic PCI code will reenable the PCI device. On the qemu
side, this runs pci_default_write_config/pci_update_mappings. Here a
changed address is returned by pci_bar_address, this is the address
which was truncated in piix_ide_reset. In case of a Xen HVM domU, the
address changes from 0xc120 to 0xc100.

While the unplug is supposed to hide the IDE disks, the changed BMIBA
address breaks the UHCI device. In case the domU has an USB tablet
configured, to recive absolute pointer coordinates for the GUI, it will
cause a hang during device discovery of the partly discovered USB hid
device. Reading the USBSTS word size register will fail. The access ends
up in the QEMU piix-bmdma device, instead of the expected uhci device.
Here a byte size request is expected, and a value of ~0 is returned. As
a result the UCHI driver sees an error state in the register, and turns
off the UHCI controller.

Fixes: e6a71ae327 ("Add support for 82371FB (Step A1) and Improved support for 
82371SB (Function 1)")

Signed-off-by: Olaf Hering <olaf@aepfle.de>
---
 hw/ide/piix.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/hw/ide/piix.c b/hw/ide/piix.c
index 41d60921e3..1e346b1b1d 100644
--- a/hw/ide/piix.c
+++ b/hw/ide/piix.c
@@ -118,7 +118,7 @@ static void piix_ide_reset(DeviceState *dev)
     pci_set_word(pci_conf + PCI_COMMAND, 0x0000);
     pci_set_word(pci_conf + PCI_STATUS,
                  PCI_STATUS_DEVSEL_MEDIUM | PCI_STATUS_FAST_BACK);
-    pci_set_byte(pci_conf + 0x20, 0x01);  /* BMIBA: 20-23h */
+    pci_set_long(pci_conf + 0x20, 0x01);  /* BMIBA: 20-23h */
 }
 
 static bool pci_piix_init_bus(PCIIDEState *d, unsigned i, Error **errp)

base-commit: d145c0da22cde391d8c6672d33146ce306e8bf75