Re: [PATCH (repost) RFC 2/2] virtio-pci: recall and return msix notifications on ISR read

[Jan Kiszka <jan.kiszka@siemens.com>]

On 2011-11-02 21:11, Michael S. Tsirkin wrote:
> MSIX spec requires that device can be operated with
> all vectors masked, by polling pending bits.
> Add APIs to recall an msix notification, and make polling
> mode possible in virtio-pci by clearing the
> pending bits and setting ISR appropriately on ISR read.
> 
> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> ---
>  hw/msix.c       |   26 ++++++++++++++++++++++++++
>  hw/msix.h       |    3 +++
>  hw/virtio-pci.c |   11 ++++++++++-
>  3 files changed, 39 insertions(+), 1 deletions(-)
> 
> diff --git a/hw/msix.c b/hw/msix.c
> index 63b41b9..fe967c9 100644
> --- a/hw/msix.c
> +++ b/hw/msix.c
> @@ -349,6 +349,32 @@ void msix_notify(PCIDevice *dev, unsigned vector)
>      stl_le_phys(address, data);
>  }
>  
> +/* Recall outstanding MSI-X notifications for a vector, if possible.
> + * Return true if any were outstanding. */
> +bool msix_recall(PCIDevice *dev, unsigned vector)
> +{
> +    bool ret;
> +    if (vector >= dev->msix_entries_nr)
> +        return false;
> +    ret = msix_is_pending(dev, vector);
> +    msix_clr_pending(dev, vector);
> +    return ret;
> +}

I would prefer to have a single API instead to clarify the tight relation:

bool msi[x]_set_notify(PCIDevice *dev, unsigned vector, unsigned level)

Would return true for level=1 if the message was either sent directly or
queued (we could deliver false if it was already queued, but I see no
use case for this yet).

Also, I don't see the generic value of some msix_recall_all. I think
it's better handled in a single loop over all vectors at caller site,
clearing the individual interrupt reason bits on a per-vector basis
there. msix_recall_all is only useful in the virtio case where you have
one vector of reason A and all the rest of B. Once you had multiple
reason C vectors as well, it would not help anymore.

Jan

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