linux-kernel - Re: [PATCH v10] vfio: ABI for mdev display dma-buf operation

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Date:   Wed, 19 Jul 2017 08:25:00 +0200
From:   Gerd Hoffmann <kraxel@...hat.com>
To:     "Zhang, Tina" <tina.zhang@...el.com>,
        Kirti Wankhede <kwankhede@...dia.com>,
        "Tian, Kevin" <kevin.tian@...el.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "intel-gfx@...ts.freedesktop.org" <intel-gfx@...ts.freedesktop.org>,
        "alex.williamson@...hat.com" <alex.williamson@...hat.com>,
        "zhenyuw@...ux.intel.com" <zhenyuw@...ux.intel.com>,
        "chris@...is-wilson.co.uk" <chris@...is-wilson.co.uk>,
        "Lv, Zhiyuan" <zhiyuan.lv@...el.com>,
        "intel-gvt-dev@...ts.freedesktop.org" 
        <intel-gvt-dev@...ts.freedesktop.org>,
        "Wang, Zhi A" <zhi.a.wang@...el.com>
Subject: Re: [PATCH v10] vfio: ABI for mdev display dma-buf operation

On Wed, 2017-07-19 at 00:16 +0000, Zhang, Tina wrote:
> > -----Original Message-----
> > From: Gerd Hoffmann [mailto:kraxel@...hat.com]
> > Sent: Monday, July 17, 2017 7:03 PM
> > To: Kirti Wankhede <kwankhede@...dia.com>; Zhang, Tina
> > <tina.zhang@...el.com>; Tian, Kevin <kevin.tian@...el.com>; linux-
> > kernel@...r.kernel.org; intel-gfx@...ts.freedesktop.org;
> > alex.williamson@...hat.com; zhenyuw@...ux.intel.com; chris@...is-
> > wilson.co.uk; Lv, Zhiyuan <zhiyuan.lv@...el.com>; intel-gvt-
> > dev@...ts.freedesktop.org; Wang, Zhi A <zhi.a.wang@...el.com>
> > Subject: Re: [PATCH v10] vfio: ABI for mdev display dma-buf
> > operation
> > 
> >   Hi,
> > 
> > > No need of flag here. If vGPU driver is not loaded in the guest,
> > > there
> > > is no surface being managed by vGPU, in that case this size will
> > > be
> > > zero.
> > 
> > Ok, we certainly have the same situation with intel.  When the
> > guest driver is not
> > loaded (yet) there is no valid surface.
> > 
> > We should cleanly define what the ioctl should do in that case, so
> > all drivers
> > behave the same way.
> > 
> > I'd suggest that all fields defining the surface (drm_format,
> > width, height, stride,
> > size) should be set to zero in that case.
> 
> Yeah, it's reasonable. How about the return value? Currently, the
> ioctl also returns "-ENODEV" in that situation.

I think it should not return an error.  Querying the plane parameters
worked fine.

cheers,
  Gerd