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

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Date:   Tue, 11 Jul 2017 11:15:59 +0200
From:   Daniel Vetter <daniel@...ll.ch>
To:     Tina Zhang <tina.zhang@...el.com>
Cc:     alex.williamson@...hat.com, kraxel@...hat.com,
        chris@...is-wilson.co.uk, zhenyuw@...ux.intel.com,
        zhiyuan.lv@...el.com, zhi.a.wang@...el.com, kevin.tian@...el.com,
        daniel@...ll.ch, kwankhede@...dia.com,
        intel-gfx@...ts.freedesktop.org,
        intel-gvt-dev@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v10] vfio: ABI for mdev display dma-buf operation

On Thu, Jul 06, 2017 at 06:29:55AM +0800, Tina Zhang wrote:
> Add VFIO_DEVICE_QUERY_GFX_PLANE ioctl command to let user mode query and
> get the plan and its related information.
> 
> The dma-buf's life cycle is handled by user mode and tracked by kernel.
> The returned fd in struct vfio_device_query_gfx_plane can be a new
> fd or an old fd of a re-exported dma-buf. Host User mode can check the
> value of fd and to see if it need to creat new resource according to the
> new fd or just use the existed resource related to the old fd.
> 
> Signed-off-by: Tina Zhang <tina.zhang@...el.com>
> 
> diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
> index ae46105..c92bc69 100644
> --- a/include/uapi/linux/vfio.h
> +++ b/include/uapi/linux/vfio.h
> @@ -502,6 +502,36 @@ struct vfio_pci_hot_reset {
>  
>  #define VFIO_DEVICE_PCI_HOT_RESET	_IO(VFIO_TYPE, VFIO_BASE + 13)
>  
> +/**
> + * VFIO_DEVICE_QUERY_GFX_PLANE - _IOW(VFIO_TYPE, VFIO_BASE + 14,
> + *                           struct vfio_device_query_gfx_plane)
> + * Return: 0 on success, -errno on failure.
> + */
> +
> +struct vfio_device_gfx_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;
> +};

Would be good to have a detailed spec of all this stuff, plus what's it
meant to be used for. I assume that e.g. start would be the opaque cookie
thing we've talked about, for dma-buf reuse? Otherwise I'm not sure what
it's good for, since the same gpu vram address can be reused for different
memory objects ...

> +
> +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;
> +};

As mentioned in the other reply already, I'm not sure what plane_type is
for. Otherwise this looks ok-ish, but hard to tell without more detailed
spec.
-Daniel

> +
> +#define VFIO_DEVICE_QUERY_GFX_PLANE _IO(VFIO_TYPE, VFIO_BASE + 14)
> +
> +
>  /* -------- API for Type1 VFIO IOMMU -------- */
>  
>  /**
> -- 
> 2.7.4
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch