linux-kernel - Re: [PATCH v6] Add udmabuf misc device

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Date:   Wed, 4 Jul 2018 09:26:39 +0200
From:   Tomeu Vizoso <tomeu.vizoso@...labora.com>
To:     Gerd Hoffmann <kraxel@...hat.com>, dri-devel@...ts.freedesktop.org,
        David Airlie <airlied@...ux.ie>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Jonathan Corbet <corbet@....net>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        Shuah Khan <shuah@...nel.org>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        "open list:DMA BUFFER SHARING FRAMEWORK" 
        <linux-media@...r.kernel.org>,
        "moderated list:DMA BUFFER SHARING FRAMEWORK" 
        <linaro-mm-sig@...ts.linaro.org>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>, Zach Reizner <zachr@...gle.com>,
        Daniel Stone <daniels@...labora.com>
Subject: Re: [PATCH v6] Add udmabuf misc device

On 07/04/2018 07:53 AM, Gerd Hoffmann wrote:
> On Tue, Jul 03, 2018 at 10:37:57AM +0200, Daniel Vetter wrote:
>> On Tue, Jul 03, 2018 at 09:53:58AM +0200, Gerd Hoffmann wrote:
>>> A driver to let userspace turn memfd regions into dma-bufs.
>>>
>>> Use case:  Allows qemu create dmabufs for the vga framebuffer or
>>> virtio-gpu ressources.  Then they can be passed around to display
>>> those guest things on the host.  To spice client for classic full
>>> framebuffer display, and hopefully some day to wayland server for
>>> seamless guest window display.
>>>
>>> qemu test branch:
>>>    https://git.kraxel.org/cgit/qemu/log/?h=sirius/udmabuf
>>>
>>> Cc: David Airlie <airlied@...ux.ie>
>>> Cc: Tomeu Vizoso <tomeu.vizoso@...labora.com>
>>> Cc: Laurent Pinchart <laurent.pinchart@...asonboard.com>
>>> Cc: Daniel Vetter <daniel@...ll.ch>
>>> Signed-off-by: Gerd Hoffmann <kraxel@...hat.com>
>>
>> I think some ack for a 2nd use-case, like virtio-wl or whatever would be
>> really cool. To give us some assurance that this is generically useful.
> 
> Tomeu?  Laurent?

Sorry, but I think I will need some help to understand how this could 
help in the virtio-wl case [adding Zach Reizner to CC].

Any graphics buffers that are allocated with memfd will be shared with 
the compositor via wl_shm, without need for dmabufs.

Daniel Stone [added to CC] commented though that this could be useful for 
browsers that composite pages with a nested Wayland compositor, to avoid 
having to blit each layer so that the EGL platform notifies the 
compositor of new contents.

Cheers,

Tomeu

>> Plus an ack from dma-buf folks (nag them on irc, you don't have them on Cc
>> here).
> 
> Hmm, does MAINTAINERS need an update then?  Maintainer and mailing lists
> listed in the "DMA BUFFER SHARING FRAMEWORK" entry are on Cc.
> 
> Who should be Cc'ed?
> 
>> Then this is imo good to go.
>>
>> I assume you'll push it to drm-misc, like all the other dma-buf stuff?
> 
> Can do that, sure, after collecting the acks ...
> 
> thanks,
>    Gerd
>