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Date: Wed, 07 Oct 2009 10:20:19 +0200
From: Avi Kivity <avi@redhat.com>
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Subject: [Qemu-devel] Re: [Qemu-commits] [COMMIT c0b1905] qemu/pci: reset
 device registers on	bus reset
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To: Anthony Liguori <aliguori@us.ibm.com>, "Michael S. Tsirkin" <mst@redhat.com>
Cc: "qemu-devel@nongnu.org" <qemu-devel@nongnu.org>, kvm-devel <kvm@vger.kernel.org>

On 10/05/2009 04:53 PM, Anthony Liguori wrote:
> From: Michael S. Tsirkin<mst@redhat.com>
>
> Reset BARs and a couple of other registers on bus reset, as per PCI
> spec.
>    

This commit breaks Windows XP restart.  After a restart Windows switches 
from 800x600 cirrus logic vga to 640x480 standard vga.  My guess is that 
this is due to two mutually-cancelling bugs:

- the bios fails to initialize one of the registers touched below
- qemu sets up that register in the state the Windows expects the bios 
to leave it in instead of the on-reset state

Once we perform the reset the register reverts to its correct reset 
state, the bios fails to initialize it, and Windows ignores the device.

I reverted this commit from qemu-kvm.git.

> diff --git a/hw/pci.c b/hw/pci.c
> index 2dd7213..e2f88ff 100644
> --- a/hw/pci.c
> +++ b/hw/pci.c
> @@ -92,7 +92,20 @@ static inline int pci_bar(int reg)
>
>   static void pci_device_reset(PCIDevice *dev)
>   {
> +    int r;
> +
>       memset(dev->irq_state, 0, sizeof dev->irq_state);
> +    dev->config[PCI_COMMAND]&= ~(PCI_COMMAND_IO | PCI_COMMAND_MEMORY |
> +                                  PCI_COMMAND_MASTER);
> +    dev->config[PCI_CACHE_LINE_SIZE] = 0x0;
> +    dev->config[PCI_INTERRUPT_LINE] = 0x0;
> +    for (r = 0; r<  PCI_NUM_REGIONS; ++r) {
> +        if (!dev->io_regions[r].size) {
> +            continue;
> +        }
> +        pci_set_long(dev->config + pci_bar(r), dev->io_regions[r].type);
> +    }
> +    pci_update_mappings(dev);
>   }
>
>   static void pci_bus_reset(void *opaque)
>
>
>    


-- 
Do not meddle in the internals of kernels, for they are subtle and quick to panic.