linux-kernel - Re: [PATCH 1/2] vfio: ABI for setting mdev display flip eventfd

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Message-ID: <20190527122237.uhd7qm62h6wfv5w7@sirius.home.kraxel.org>
Date:   Mon, 27 May 2019 14:22:37 +0200
From:   Gerd Hoffmann <kraxel@...hat.com>
To:     Zhenyu Wang <zhenyuw@...ux.intel.com>
Cc:     Tina Zhang <tina.zhang@...el.com>,
        intel-gvt-dev@...ts.freedesktop.org, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, alex.williamson@...hat.com,
        hang.yuan@...el.com, zhiyuan.lv@...el.com
Subject: Re: [PATCH 1/2] vfio: ABI for setting mdev display flip eventfd

On Mon, May 27, 2019 at 05:07:41PM +0800, Zhenyu Wang wrote:
> On 2019.05.27 16:43:11 +0800, Tina Zhang wrote:
> > Add VFIO_DEVICE_SET_GFX_FLIP_EVENTFD ioctl command to set eventfd
> > based signaling mechanism to deliver vGPU framebuffer page flip
> > event to userspace.
> 
> Should we add probe to see if driver can support gfx flip event?

Userspace can simply call VFIO_DEVICE_SET_GFX_FLIP_EVENTFD and see if it
worked.  If so -> use the eventfd.  Otherwise take the fallback path
(timer based polling).  I can't see any advantage a separate feature
probe steps adds.

cheers,
  Gerd