RE: [PATCH v8 4/6] vfio: Define vfio based vgpu's dma-buf operations

[Chen, Xiaoguang]

>-----Original Message-----
>From: Alex Williamson [mailto:alex.williamson@xxxxxxxxxx]
>Sent: Wednesday, June 14, 2017 5:25 AM
>To: Chen, Xiaoguang <xiaoguang.chen@xxxxxxxxx>
>Cc: kraxel@xxxxxxxxxx; chris@xxxxxxxxxxxxxxxxxx; intel-
>gfx@xxxxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx;
>zhenyuw@xxxxxxxxxxxxxxx; Lv, Zhiyuan <zhiyuan.lv@xxxxxxxxx>; intel-gvt-
>dev@xxxxxxxxxxxxxxxxxxxxx; Wang, Zhi A <zhi.a.wang@xxxxxxxxx>; Tian, Kevin
><kevin.tian@xxxxxxxxx>
>Subject: Re: [PATCH v8 4/6] vfio: Define vfio based vgpu's dma-buf operations
>
>On Fri,  9 Jun 2017 14:50:40 +0800
>Xiaoguang Chen <xiaoguang.chen@xxxxxxxxx> wrote:
>
>> Here we defined a new ioctl to create a fd for a vfio device based on
>> the input type. Now only one type is supported that is a dma-buf
>> management fd.
>> Two ioctls are defined for the dma-buf management fd: query the vfio
>> vgpu's plane information and create a dma-buf for a plane.
>>
>> Signed-off-by: Xiaoguang Chen <xiaoguang.chen@xxxxxxxxx>
>> ---
>>  include/uapi/linux/vfio.h | 58
>> +++++++++++++++++++++++++++++++++++++++++++++++
>>  1 file changed, 58 insertions(+)
>>
>> diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
>> index ae46105..24427b7 100644
>> --- a/include/uapi/linux/vfio.h
>> +++ b/include/uapi/linux/vfio.h
>> @@ -502,6 +502,64 @@ struct vfio_pci_hot_reset {
>>
>>  #define VFIO_DEVICE_PCI_HOT_RESET	_IO(VFIO_TYPE, VFIO_BASE + 13)
>>
>> +/**
>> + * VFIO_DEVICE_GET_FD - _IO(VFIO_TYPE, VFIO_BASE + 14, __u32)
>> + *
>> + * Create a fd for a vfio device based on the input type
>> + * Vendor driver should handle this ioctl to create a fd and manage
>> +the
>> + * life cycle of this fd.
>> + *
>> + * Return: a fd if vendor support that type, -errno if not supported
>> +*/
>> +
>> +#define VFIO_DEVICE_GET_FD	_IO(VFIO_TYPE, VFIO_BASE + 14)
>> +
>> +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;
>> +};
>> +
>> +#define VFIO_DEVICE_DMABUF_MGR_FD	0 /* Supported fd types */
>
>Move this #define up above vfio_vgpu_plane_info to associate it with the
>VFIO_DEVICE_GET_FD ioctl.
OK.

>
>> +
>> +/*
>> + * VFIO_DEVICE_QUERY_PLANE - _IO(VFIO_TYPE, VFIO_BASE + 15,
>> + *						struct vfio_vgpu_query_plane)
>> + * Query plane information
>> + */
>> +struct vfio_vgpu_query_plane {
>> +	__u32 argsz;
>> +	__u32 flags;
>> +	struct vfio_vgpu_plane_info plane_info;
>> +	__u32 plane_id;
>> +	__u32 padding;
>
>This padding doesn't make sense.
This padding is still needed if we do not move the plane_id into vfio_vgpu_plane_info. Right?

>
>> +};
>> +
>> +#define VFIO_DEVICE_QUERY_PLANE _IO(VFIO_TYPE, VFIO_BASE + 15)
>> +
>> +/*
>> + * VFIO_DEVICE_CREATE_DMABUF - _IO(VFIO, VFIO_BASE + 16,
>> + *						struct
>vfio_vgpu_create_dmabuf)
>> + *
>> + * Create a dma-buf for a plane
>> + */
>> +struct vfio_vgpu_create_dmabuf {
>> +	__u32 argsz;
>> +	__u32 flags;
>> +	struct vfio_vgpu_plane_info plane_info;
>> +	__s32 fd;
>> +	__u32 plane_id;
>> +};
>
>Both of these have a plane_id, should plane_id simply replace the padding in
>plane_info?  
Precisely speaking plane_id does not belong to the plane info. All the other information are decoded from plane except plane id.

>If not, let's at least put them in the same order so that plane_id is
>after plane_info for both structs.
Ok. 

>
>> +
>> +#define VFIO_DEVICE_CREATE_DMABUF _IO(VFIO_TYPE, VFIO_BASE + 16)
>
>I don't think these should be named just VFIO_DEVICE_foo, that implies they're
>ioctls on the vfio device fd, they're not.  They need to be associated both in name
>and more complete descriptions as ioctls to the fd returned from a request for a
>VFIO_DEVICE_DMABUF_MGR_FD.  Perhaps VFIO_DMABUF_MGR_QUERY_PLANE
>and VFIO_DMABUF_MGR_CREATE_DMABUF.  I'm also not sure why we're using
>"vgpu" in the structure names here either, the ioctls aren't named after vgpus.
>Aren't these rather generic to graphics dmabufs, not specifically vgpus?  
Make sense. I will change the names.

Thanks,
>
>Alex
>
>> +
>>  /* -------- API for Type1 VFIO IOMMU -------- */
>>
>>  /**