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Subject: Re: [virtio-dev] [PATCH] pci: set ISR bit on config change with MSI-X


"Michael S. Tsirkin" <mst@redhat.com> writes:
> config changes are slow path anyway, so we
> can as well set ISR bit to help drivers detect changes.
>
> This allows sharing config interrupts which is what
> issue reporter seems to ask for.

This seems a reasonable compromise.  If the device doesn't want
to read ISR Status, it doesn't have to.

Thanks,
Rusty.

>
> VIRTIO-104
>
> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> ---
>  content.tex | 12 ++++++++++--
>  1 file changed, 10 insertions(+), 2 deletions(-)
>
> diff --git a/content.tex b/content.tex
> index 5936154..7f1eecb 100644
> --- a/content.tex
> +++ b/content.tex
> @@ -1396,6 +1396,14 @@ See sections \ref{sec:Virtio Transport Options / Virtio Over PCI Bus / PCI-speci
>  
>  The device MUST present at least one VIRTIO_PCI_CAP_ISR_CFG capability.  
>  
> +The device MUST set the Device Configuration Interrupt bit
> +in \field{ISR status} before sending a device configuration
> +change notification to the driver.
> +
> +If MSI-X capability is disabled, the device MUST set the Queue
> +Interrupt bit in \field{ISR status} before sending a virtqueue
> +notification to the driver.
> +
>  If MSI-X capability is disabled, the device MUST set the Interrupt Status
>  bit in the PCI Status register in the PCI Configuration Header of
>  the device to the logical OR of all bits in \field{ISR status} of
> @@ -1406,8 +1414,8 @@ The device MUST reset \field{ISR status} to 0 on driver read.
>  
>  \drivernormative{\paragraph}{ISR status capability}{Virtio Transport Options / Virtio Over PCI Bus / PCI Device Layout / ISR status capability}
>  
> -The driver MUST NOT access the ISR field when MSI-X capability
> -is enabled.
> +If MSI-X capability is enabled, the driver SHOULD NOT access
> +\field{ISR status} upon detecting a Queue Interrupt.
>  
>  \subsubsection{Device-specific configuration}\label{sec:Virtio Transport Options / Virtio Over PCI Bus / PCI Device Layout / Device-specific configuration}
>  
> -- 
> MST
>
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