linux-kernel - Re: [PATCH v6 4/6] vfio: Define vfio based vgpu's dma-buf operations

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Date:   Fri, 2 Jun 2017 00:16:42 +0530
From:   Kirti Wankhede <kwankhede@...dia.com>
To:     Alex Williamson <alex.williamson@...hat.com>,
        "Chen, Xiaoguang" <xiaoguang.chen@...el.com>
CC:     Gerd Hoffmann <kraxel@...hat.com>,
        "chris@...is-wilson.co.uk" <chris@...is-wilson.co.uk>,
        "intel-gfx@...ts.freedesktop.org" <intel-gfx@...ts.freedesktop.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "zhenyuw@...ux.intel.com" <zhenyuw@...ux.intel.com>,
        "Lv, Zhiyuan" <zhiyuan.lv@...el.com>,
        "intel-gvt-dev@...ts.freedesktop.org" 
        <intel-gvt-dev@...ts.freedesktop.org>,
        "Wang, Zhi A" <zhi.a.wang@...el.com>,
        "Tian, Kevin" <kevin.tian@...el.com>
Subject: Re: [PATCH v6 4/6] vfio: Define vfio based vgpu's dma-buf operations



On 6/1/2017 10:08 PM, Alex Williamson wrote:
> On Thu, 1 Jun 2017 03:01:28 +0000
> "Chen, Xiaoguang" <xiaoguang.chen@...el.com> wrote:
> 
>> Hi Kirti,
>>
>>> -----Original Message-----
>>> From: Kirti Wankhede [mailto:kwankhede@...dia.com]
>>> Sent: Thursday, June 01, 2017 1:23 AM
>>> To: Chen, Xiaoguang <xiaoguang.chen@...el.com>; Gerd Hoffmann
>>> <kraxel@...hat.com>; alex.williamson@...hat.com; chris@...is-wilson.co.uk;
>>> intel-gfx@...ts.freedesktop.org; linux-kernel@...r.kernel.org;
>>> zhenyuw@...ux.intel.com; Lv, Zhiyuan <zhiyuan.lv@...el.com>; intel-gvt-
>>> dev@...ts.freedesktop.org; Wang, Zhi A <zhi.a.wang@...el.com>; Tian, Kevin
>>> <kevin.tian@...el.com>
>>> Subject: Re: [PATCH v6 4/6] vfio: Define vfio based vgpu's dma-buf operations
>>>
>>>
>>>
>>> On 5/31/2017 11:48 AM, Chen, Xiaoguang wrote:  
>>>> Hi,
>>>>  
>>>>> -----Original Message-----
>>>>> From: Gerd Hoffmann [mailto:kraxel@...hat.com]
>>>>> Sent: Monday, May 29, 2017 3:20 PM
>>>>> To: Chen, Xiaoguang <xiaoguang.chen@...el.com>;
>>>>> alex.williamson@...hat.com; chris@...is-wilson.co.uk; intel-
>>>>> gfx@...ts.freedesktop.org; linux-kernel@...r.kernel.org;
>>>>> zhenyuw@...ux.intel.com; Lv, Zhiyuan <zhiyuan.lv@...el.com>;
>>>>> intel-gvt- dev@...ts.freedesktop.org; Wang, Zhi A
>>>>> <zhi.a.wang@...el.com>; Tian, Kevin <kevin.tian@...el.com>
>>>>> Subject: Re: [PATCH v6 4/6] vfio: Define vfio based vgpu's dma-buf
>>>>> operations
>>>>>  
>>>>>> +struct vfio_vgpu_dmabuf_info {
>>>>>> +	__u32 argsz;
>>>>>> +	__u32 flags;
>>>>>> +	struct vfio_vgpu_plane_info plane_info;
>>>>>> +	__s32 fd;
>>>>>> +	__u32 pad;
>>>>>> +};  
>>>>>
>>>>> Hmm, now you have argsz and flags twice in vfio_vgpu_dmabuf_info ...
>>>>>
>>>>> I think we should have something like this:
>>>>>
>>>>> struct vfio_vgpu_plane_info {
>>>>>         __u64 start;
>>>>>         __u64 drm_format_mod;
>>>>>         __u32 drm_format;
>>>>>         __u32 width;
>>>>>         __u32 height;
>>>>>         __u32 stride;
>>>>>         __u32 size;
>>>>>         __u32 x_pos;
>>>>>         __u32 y_pos;
>>>>>        __u32 padding;
>>>>> };
>>>>>
>>>>> struct vfio_vgpu_query_plane {
>>>>> 	__u32 argsz;
>>>>> 	__u32 flags;
>>>>> 	struct vfio_vgpu_plane_info plane_info;
>>>>>        __u32 plane_id;
>>>>>        __u32 padding;
>>>>> };
>>>>>
>>>>> struct vfio_vgpu_create_dmabuf {
>>>>> 	__u32 argsz;
>>>>> 	__u32 flags;
>>>>> 	struct vfio_vgpu_plane_info plane_info;
>>>>>        __u32 plane_id;
>>>>>        __s32 fd;
>>>>> };  
>>>> Good suggestion will apply in the next version.
>>>> Thanks for review :)
>>>>  
>>>
>>> Can you define what are the expected values of 'flags' would be?  
>> Flags is not used in this case.  It is defined to follow the rules of vfio ioctls.
> 
> An important note about flags, the vendor driver must validate it.  If
> they don't and the user passes an arbitrary value there, then we have a
> backwards compatibility issue with ever attempting to use the flags
> field.  The user passing in a flag unknown to the vendor driver should
> return an -EINVAL response.  In this case, we haven't defined any
> flags, so the vendor driver needs to force the user to pass zero.

There are two ways QEMU can get surface for console:
1. adding a region using region capability
2. dmabuf

In both the above case surface parameters need to be queried from vendor
driver are same. The structure would be :

struct vfio_vgpu_surface_info {
        __u64 start;
        __u32 width;
        __u32 height;
        __u32 stride;
        __u32 size;
        __u32 x_pos;
        __u32 y_pos;
        __u32 padding;
        /* Only used when VFIO_VGPU_SURFACE_DMABUF_* flags set */
        __u64 drm_format_mod;
        __u32 drm_format;
};

We can use one ioctl to query surface information from vendor driver,
structure would look like:

struct vfio_vgpu_get_surface_info{
	__u32 argsz;
	__u32 flags;
#define VFIO_VGPU_SURFACE_DMABUF_CREATE	(1 << 0) /* Create dmabuf */
#define VFIO_VGPU_SURFACE_DMABUF_QUERY	(1 << 1) /* Query surface info
for dmabuf */
#define VFIO_VGPU_SURFACE_REGION_QUERY	(1 << 2) /* Query surface info
for REGION type  */
	struct vfio_vgpu_surface_info surface;
        __u32 plane_id;
        __s32 fd;
};

#define VFIO_DEVICE_SURFACE_INFO _IO(VFIO_TYPE, VFIO_BASE + 15)

Vendor driver should return -EINVAL, if that type of query is not
supported.

I would like to design this interface to support both type, region cap
and dmabuf.

Thanks,
Kirti