Re: [RFC PATCH v4 2/6] vfio: Introduce vGPU display irq type

[Alex Williamson <alex.williamson@redhat.com>]

On Mon, 22 Jul 2019 05:28:35 +0000
"Lu, Kechen" <kechen.lu@intel.com> wrote:

> Hi, 
> 
> > -----Original Message-----
> > From: Alex Williamson [mailto:alex.williamson@redhat.com]
> > Sent: Saturday, July 20, 2019 12:25 AM
> > To: Lu, Kechen <kechen.lu@intel.com>
> > Cc: intel-gvt-dev@lists.freedesktop.org; kvm@vger.kernel.org; linux-
> > kernel@vger.kernel.org; Zhang, Tina <tina.zhang@intel.com>;
> > kraxel@redhat.com; zhenyuw@linux.intel.com; Lv, Zhiyuan
> > <zhiyuan.lv@intel.com>; Wang, Zhi A <zhi.a.wang@intel.com>; Tian, Kevin
> > <kevin.tian@intel.com>; Yuan, Hang <hang.yuan@intel.com>
> > Subject: Re: [RFC PATCH v4 2/6] vfio: Introduce vGPU display irq type
> > 
> > On Thu, 18 Jul 2019 23:56:36 +0800
> > Kechen Lu <kechen.lu@intel.com> wrote:
> >   
> > > From: Tina Zhang <tina.zhang@intel.com>
> > >
> > > Introduce vGPU specific irq type VFIO_IRQ_TYPE_GFX, and
> > > VFIO_IRQ_SUBTYPE_GFX_DISPLAY_IRQ as the subtype for vGPU display
> > >
> > > Signed-off-by: Tina Zhang <tina.zhang@intel.com>
> > > ---
> > >  include/uapi/linux/vfio.h | 3 +++
> > >  1 file changed, 3 insertions(+)
> > >
> > > diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
> > > index be6adab4f759..df28b17a6e2e 100644
> > > --- a/include/uapi/linux/vfio.h
> > > +++ b/include/uapi/linux/vfio.h
> > > @@ -469,6 +469,9 @@ struct vfio_irq_info_cap_type {
> > >  	__u32 subtype;  /* type specific */
> > >  };
> > >
> > > +#define VFIO_IRQ_TYPE_GFX				(1)
> > > +#define VFIO_IRQ_SUBTYPE_GFX_DISPLAY_IRQ		(1)
> > > +  
> > 
> > Please include a description defining exactly what this IRQ is intended to signal.
> > For instance, if another vGPU vendor wanted to implement this in their driver
> > and didn't have the QEMU code for reference to what it does with the IRQ, what
> > would they need to know?  Thanks,
> > 
> > Alex
> >   
> 
> Yes, that makes more sense. I'll add the description for it at next version patch.
> 
> BTW, may I have one more question? In the current design ideas, we partitioned 
> the vGPU display eventfd counted 8-byte value into at most 8 events to deliver 
> multiple display events, so we need different increasement counter value to 
> differentiate the events. As this is the exposed thing the QEMU has to know, we
> plan adds a macro here VFIO_IRQ_SUBTYPE_GFX_DISPLAY_EVENTFD_BASE_SHIFT to
> make sure the partitions shift in 1 byte, does it make sense putting here? Looking  
> forward to your and Gerd's comments. Thanks!

Couldn't you expose this as another capability within the IRQ_INFO
return data?  If you were to define it as a macro, I assume that means
it would be hard coded, in which case this probably becomes an Intel
specific IRQ, rather than what appears to be framed as a generic
graphics IRQ extension.  A new capability could instead allow the
vendor to specify their own value, where we could define how userspace
should interpret and make use of this value.  Thanks,

Alex