linux-kernel - Re: [PATCH v9 5/7] vfio: Define vfio based dma-buf operations

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Message-ID: <5cf2c46d-3d3b-5b7a-227f-8bb26a6c835a@nvidia.com>
Date:   Tue, 20 Jun 2017 19:05:19 +0530
From:   Kirti Wankhede <kwankhede@...dia.com>
To:     Alex Williamson <alex.williamson@...hat.com>,
        Gerd Hoffmann <kraxel@...hat.com>
CC:     Xiaoguang Chen <xiaoguang.chen@...el.com>,
        <chris@...is-wilson.co.uk>, <intel-gfx@...ts.freedesktop.org>,
        <linux-kernel@...r.kernel.org>, <zhenyuw@...ux.intel.com>,
        <zhiyuan.lv@...el.com>, <intel-gvt-dev@...ts.freedesktop.org>,
        <zhi.a.wang@...el.com>, <kevin.tian@...el.com>
Subject: Re: [PATCH v9 5/7] vfio: Define vfio based dma-buf operations



On 6/19/2017 8:25 PM, Alex Williamson wrote:
> On Mon, 19 Jun 2017 08:38:32 +0200
> Gerd Hoffmann <kraxel@...hat.com> wrote:
> 
>>   Hi,
>>
>>> My suggestion was to use vfio device fd for this ioctl and have
>>> dmabuf
>>> mgr fd as member in above query_plane structure, for region type it
>>> would be set to 0.  
>>
>> Region type should be DRM_PLANE_TYPE_PRIMARY
>>
>>> Can't mmap that page to get surface information. There is no way to
>>> synchronize between QEMU reading this mmapped region and vendor
>>> driver
>>> writing it. There could be race condition in these two operations.
>>> Read
>>> on this page should be trapped and blocking, so that surface in that
>>> region is only updated when its asked for.  
>>
>> Does it make sense to have a "generation" field in the plane_info
>> struct (which gets increased each time the struct changes) ?
> 
> It seems less cumbersome than checking each field to see if it has
> changed.  Thanks,
> 

Looks good. And vendor driver should take care of rounding up the value
when it reaches its max limit.

Thanks,
Kirti


> Alex
>