Re: [PATCH v2 26/30] vfio-pci/zdev: wire up zPCI adapter interrupt forwarding support

[Matthew Rosato]

On 1/19/22 12:10 PM, Pierre Morel wrote:
> On 1/14/22 21:31, Matthew Rosato wrote:
...
> > diff --git a/include/uapi/linux/vfio_zdev.h 
> > b/include/uapi/linux/vfio_zdev.h
> > index 575f0410dc66..c574e23f9385 100644
> > --- a/include/uapi/linux/vfio_zdev.h
> > +++ b/include/uapi/linux/vfio_zdev.h
> > @@ -90,4 +90,24 @@ struct vfio_device_zpci_interp {
> >       __u32 fh;        /* Host device function handle */
> >   };
> > +/**
> > + * VFIO_DEVICE_FEATURE_ZPCI_AIF
> > + *
> > + * This feature is used for enabling forwarding of adapter interrupts 
> > directly
> > + * from firmware to the guest.  When setting this feature, the flags 
> > indicate
> > + * whether to enable/disable the feature and the structure defined 
> > below is
> > + * used to setup the forwarding structures.  When getting this 
> > feature, only
> > + * the flags are used to indicate the current state.
> > + */
> > +struct vfio_device_zpci_aif {
> > +    __u64 flags;
> > +#define VFIO_DEVICE_ZPCI_FLAG_AIF_FLOAT 1
> > +#define VFIO_DEVICE_ZPCI_FLAG_AIF_HOST 2
>
> Generaly it looks good to me but I miss some explanation on these flags.

I can add a small line comment for each, like:

 AIF_FLOAT 1 /* Floating interrupts enabled */
 AIF_HOST 2  /* Host delivery forced */

But here's a bit more detail:

On SET:
AIF_FLOAT = 1 means enable the interrupt forwarding assist for floating 
interrupt delivery
AIF_FLOAT = 0 means to disable it.
AIF_HOST = 1 means the assist will always deliver the interrupt to the 
host and let the host inject it
AIF_HOST = 0 host only gets interrupts when firmware can't deliver

on GET, we just indicate the current settings from the most recent SET, 
meaning:
AIF_FLOAT = 1 interrupt forwarding assist is currently active
AIF_FLOAT = 0 interrupt forwarding assist is not currently active
AIF_HOST = 1 interrupt forwarding will always go through host
AIF_HOST = 0 interrupt forwarding will only go through the host when 
necessary

> Which makes me realize that a more complete documentation under 
> Documentation/S390 for VFIO zPCI as we have for VFIO AP and VFIO CCW 
> would be of great interest.

You're not wrong -- a similar comment came up for QEMU.  I will add this 
to my todo list as a follow-on.