Re: [Qemu-devel] [RfC PATCH 04/15] virtio-pci: make modern bar 64bit prefetchable

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

On Mon, Feb 23, 2015 at 11:23:20AM +0100, Gerd Hoffmann wrote:
> Modern bar is made prefetchable.  In case it is configured to use one of
> the bars 0, 2, or 4 (which by default is the case) it is also configured
> as 64bit region.
> 
> Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

Fine, but I can't apply this without 3/15.

> ---
>  hw/virtio/virtio-pci.c | 12 +++++++++---
>  1 file changed, 9 insertions(+), 3 deletions(-)
> 
> diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c
> index f97baf2..96b3692 100644
> --- a/hw/virtio/virtio-pci.c
> +++ b/hw/virtio/virtio-pci.c
> @@ -1263,7 +1263,8 @@ static void virtio_pci_device_plugged(DeviceState *d)
>          pci_set_word(config + PCI_DEVICE_ID,
>                       0x1040 + virtio_bus_get_vdev_id(bus));
>          pci_config_set_revision(config, 1);
> -        if (proxy->msix_bar == proxy->modern_mem_bar) {
> +        if ((proxy->msix_bar == proxy->modern_mem_bar) ||
> +            (proxy->msix_bar == proxy->modern_mem_bar+1)) {
>              proxy->msix_bar = (proxy->msix_bar + 2) % 6;
>          }
>      }

I'd like to avoid extra (), and see space around +.
E.g.
        if (proxy->msix_bar == proxy->modern_mem_bar ||
            proxy->msix_bar == proxy->modern_mem_bar + 1)

we can generally rely on C to DTRT wrt priority of arithmentic
operations and comparisons.

> @@ -1301,6 +1302,7 @@ static void virtio_pci_device_plugged(DeviceState *d)
>                                        VIRTIO_PCI_QUEUE_MAX),
>              .notify_off_multiplier = cpu_to_le32(QEMU_VIRTIO_PCI_QUEUE_MEM_MULT),
>          };
> +        uint32_t modern_mem_attr;
>  
>          static const MemoryRegionOps common_ops = {
>              .read = virtio_pci_common_read,
> @@ -1374,9 +1376,13 @@ static void virtio_pci_device_plugged(DeviceState *d)
>                                QEMU_VIRTIO_PCI_QUEUE_MEM_MULT *
>                                VIRTIO_PCI_QUEUE_MAX);
>          memory_region_add_subregion(&proxy->modern_bar, 0x3000, &proxy->notify);
> +        modern_mem_attr = (PCI_BASE_ADDRESS_SPACE_MEMORY |
> +                           PCI_BASE_ADDRESS_MEM_PREFETCH);

no need for () to the right of =.

> +        if (!(proxy->modern_mem_bar % 2)) {
> +            modern_mem_attr |= PCI_BASE_ADDRESS_MEM_TYPE_64;
> +        }

That's pretty unexpected.
This kind of hack seems to show why it's not a good idea
to let device play with layouts.

>          pci_register_bar(&proxy->pci_dev, proxy->modern_mem_bar,
> -                         PCI_BASE_ADDRESS_SPACE_MEMORY,
> -                         &proxy->modern_bar);
> +                         modern_mem_attr, &proxy->modern_bar);
>      }
>  
>      if (proxy->nvectors &&
> -- 
> 1.8.3.1