linux-kernel - Re: [PATCH v17 5/6] vfio: ABI for mdev display dma-buf operation

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Message-ID: <20171109135457.4f7514d3@t450s.home>
Date:   Thu, 9 Nov 2017 13:54:57 -0700
From:   Alex Williamson <alex.williamson@...hat.com>
To:     Gerd Hoffmann <kraxel@...hat.com>
Cc:     Tina Zhang <tina.zhang@...el.com>, chris@...is-wilson.co.uk,
        joonas.lahtinen@...ux.intel.com, zhenyuw@...ux.intel.com,
        zhiyuan.lv@...el.com, zhi.a.wang@...el.com, kevin.tian@...el.com,
        daniel@...ll.ch, kwankhede@...dia.com, hang.yuan@...el.com,
        intel-gfx@...ts.freedesktop.org,
        intel-gvt-dev@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        Daniel Vetter <daniel.vetter@...ll.ch>
Subject: Re: [PATCH v17 5/6] vfio: ABI for mdev display dma-buf operation

On Thu, 9 Nov 2017 19:35:14 +0100
Gerd Hoffmann <kraxel@...hat.com> wrote:

>   Hi,
> 
> > struct vfio_device_gfx_plane_info lacks the head field we've been
> > discussing.  Thanks,  
> 
> Adding multihead support turned out to not be that easy.  There are
> corner cases like a single framebuffer spawning both heads.  Also it
> would be useful to somehow hint to the guest which heads it should use.
> 
> In short:  Proper multihead support is more complex than just adding a
> head field for later use.  So in a short private discussion with Tina we
> came to the conclusion that it will be better add multihead support to
> the API when the first driver wants use it, so we can actually test the
> interface and make sure we didn't miss anything.  Adding a incomplete
> multihead API now doesn't help anybody.

Do you think we can enable multi-head and preserve backwards
compatibility within this API proposed here?  Thanks,

Alex