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

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Message-ID: <20171109183514.w3tbqumovglr4sri@sirius.home.kraxel.org>
Date:   Thu, 9 Nov 2017 19:35:14 +0100
From:   Gerd Hoffmann <kraxel@...hat.com>
To:     Alex Williamson <alex.williamson@...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

  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.

cheers,
  Gerd