Re: [PATCH v10] vfio: ABI for mdev display dma-buf operation

[Kirti Wankhede]

On 7/14/2017 7:00 AM, Zhang, Tina wrote:
> 
> 
>> -----Original Message-----
>> From: intel-gvt-dev [mailto:intel-gvt-dev-bounces@xxxxxxxxxxxxxxxxxxxxx] On
>> Behalf Of Kirti Wankhede
>> Sent: Wednesday, July 12, 2017 8:45 PM
>> To: Zhang, Tina <tina.zhang@xxxxxxxxx>; Gerd Hoffmann
>> <kraxel@xxxxxxxxxx>; Tian, Kevin <kevin.tian@xxxxxxxxx>; linux-
>> kernel@xxxxxxxxxxxxxxx; intel-gfx@xxxxxxxxxxxxxxxxxxxxx;
>> alex.williamson@xxxxxxxxxx; zhenyuw@xxxxxxxxxxxxxxx; chris@chris-
>> wilson.co.uk; Lv, Zhiyuan <zhiyuan.lv@xxxxxxxxx>; intel-gvt-
>> dev@xxxxxxxxxxxxxxxxxxxxx; Wang, Zhi A <zhi.a.wang@xxxxxxxxx>
>> Subject: Re: [PATCH v10] vfio: ABI for mdev display dma-buf operation
>>
>>
>>
>> On 7/12/2017 1:10 PM, Daniel Vetter wrote:
>>> On Wed, Jul 12, 2017 at 02:31:40AM +0000, Zhang, Tina wrote:
>>>>
>>>>
>>>>> -----Original Message-----
>>>>> From: intel-gvt-dev
>>>>> [mailto:intel-gvt-dev-bounces@xxxxxxxxxxxxxxxxxxxxx] On Behalf Of
>>>>> Daniel Vetter
>>>>> Sent: Tuesday, July 11, 2017 5:13 PM
>>>>> To: Gerd Hoffmann <kraxel@xxxxxxxxxx>
>>>>> Cc: Tian, Kevin <kevin.tian@xxxxxxxxx>;
>>>>> linux-kernel@xxxxxxxxxxxxxxx; intel- gfx@xxxxxxxxxxxxxxxxxxxxx;
>>>>> alex.williamson@xxxxxxxxxx; zhenyuw@xxxxxxxxxxxxxxx;
>>>>> chris@xxxxxxxxxxxxxxxxxx; Kirti Wankhede <kwankhede@xxxxxxxxxx>; Lv,
>>>>> Zhiyuan <zhiyuan.lv@xxxxxxxxx>; daniel@xxxxxxxx; Zhang, Tina
>>>>> <tina.zhang@xxxxxxxxx>; intel-gvt- dev@xxxxxxxxxxxxxxxxxxxxx; Wang,
>>>>> Zhi A <zhi.a.wang@xxxxxxxxx>
>>>>> Subject: Re: [PATCH v10] vfio: ABI for mdev display dma-buf
>>>>> operation
>>>>>
>>>>> On Tue, Jul 11, 2017 at 08:14:08AM +0200, Gerd Hoffmann wrote:
>>>>>>   Hi,
>>>>>>
>>>>>>>> +struct vfio_device_query_gfx_plane {
>>>>>>>> +	__u32 argsz;
>>>>>>>> +	__u32 flags;
>>>>>>>> +	struct vfio_device_gfx_plane_info plane_info;
>>>>>>>> +	__u32 plane_type;
>>>>>>>> +	__s32 fd; /* dma-buf fd */
>>>>>>>> +	__u32 plane_id;
>>>>>>>> +};
>>>>>>>> +
>>>>>>>
>>>>>>> It would be better to have comment here about what are expected
>>>>>>> values for plane_type and plane_id.
>>>>>>
>>>>>> plane_type is DRM_PLANE_TYPE_*.
>>>>>>
>>>>>> yes, a comment saying so would be good, same for drm_format which
>>>>>> is DRM_FORMAT_*.  While looking at these two: renaming plane_type
>>>>>> to drm_plane_type (for consistency) is probably a good idea too.
>>>>>>
>>>>>> plane_id needs a specification.
>>>>>
>>>>> Why do you need plane_type? With universal planes the plane_id along
>>>>> is sufficient to identify a plane on a given drm device instance. I'd just
>> remove it.
>>>>> -Daniel
>>>> The plane_type here, is to ask the mdev vendor driver to return the
>> information according to the value in field plane_type. So, it's a input field.
>>>> The values in plane_type field is the same of drm_plane_type. And yes, it's
>> better to use drm_plane_type instead of plane_id.
>>>
>>> I have no idea what you mean here, I guess that just shows that
>>> discussing an ioctl struct without solid definitions of what field
>>> does what and why is not all that useful. What exactly it plane_id for then?
>>>
>>
>> plane type could be DRM_PLANE_TYPE_PRIMARY or
>> DRM_PLANE_TYPE_CURSOR.
>>
>> In case when VFIO region is used to provide surface to QEMU, plane_id would
>> be region index, for example region 10 could be used for primary surface and
>> region 11 could be used for cursor surface. So in that case, mdev vendor driver
>> should return plane_type and its corresponding plane_id.

> Thanks, Kirti, do you mean there will be multiple DRM_PLANE_TYPE_PRIMARY and multiple DRM_PLANE_TYPE_CURSOR planes existing in the same time and region usage needs to use plane_id to distinguish among them? Is it for the multiple output or that's the typical way of region usage? Thanks.

There could be only two planes, one DRM_PLANE_TYPE_PRIMARY and one
DRM_PLANE_TYPE_CURSOR.
Steps from gfx_update for region case would be:
- VFIO_DEVICE_QUERY_GFX_PLANE with plane_type = DRM_PLANE_TYPE_PRIMARY
- if vfio_device_gfx_plane_info.size > 0, read region for primary
surface and update console surface
- VFIO_DEVICE_QUERY_GFX_PLANE with plane_type = DRM_PLANE_TYPE_CURSOR
- if vfio_device_gfx_plane_info.size > 0, read region for cursor surface
update cursor on surface.

Thanks,
Kirti


> 
> Tina
> 
>>
>> Thanks,
>> Kirti
>>
>>> This just confused me more ...
>>> -Daniel
>>>
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