[PATCH 3/6] dma-buf: Add ioctls to allow userspace to flush

[Hwang, Dongseong]

On Thu, Aug 27, 2015 at 2:29 AM, Tiago Vignatti
<tiago.vignatti at intel.com> wrote:
> From: Daniel Vetter <daniel.vetter at ffwll.ch>
>
> The userspace might need some sort of cache coherency management e.g. when CPU
> and GPU domains are being accessed through dma-buf at the same time. To
> circumvent this problem there are begin/end coherency markers, that forward
> directly to existing dma-buf device drivers vfunc hooks. Userspace can make use
> of those markers through the DMA_BUF_IOCTL_SYNC ioctl. The sequence would be
> used like following:
>      - mmap dma-buf fd
>      - for each drawing/upload cycle in CPU 1. SYNC_START ioctl, 2. read/write
>        to mmap area 3. SYNC_END ioctl. This can be repeated as often as you
>        want (with the new data being consumed by the GPU or say scanout device)
>      - munamp once you don't need the buffer any more
>
> v2 (Tiago): Fix header file type names (u64 -> __u64)
> v3 (Tiago): Add documentation. Use enum dma_buf_sync_flags to the begin/end
> dma-buf functions. Check for overflows in start/length.
> v4 (Tiago): use 2d regions for sync.
> v5 (Tiago): forget about 2d regions (v4); use _IOW in DMA_BUF_IOCTL_SYNC and
> remove range information from struct dma_buf_sync.
>
> Cc: Sumit Semwal <sumit.semwal at linaro.org>
> Signed-off-by: Daniel Vetter <daniel.vetter at intel.com>
> Signed-off-by: Tiago Vignatti <tiago.vignatti at intel.com>
> ---
>  Documentation/dma-buf-sharing.txt | 12 +++++++++++
>  drivers/dma-buf/dma-buf.c         | 43 +++++++++++++++++++++++++++++++++++++++
>  include/uapi/linux/dma-buf.h      | 41 +++++++++++++++++++++++++++++++++++++
>  3 files changed, 96 insertions(+)
>  create mode 100644 include/uapi/linux/dma-buf.h
>
> diff --git a/Documentation/dma-buf-sharing.txt b/Documentation/dma-buf-sharing.txt
> index 4f4a84b..ec0ab1d 100644
> --- a/Documentation/dma-buf-sharing.txt
> +++ b/Documentation/dma-buf-sharing.txt
> @@ -352,6 +352,18 @@ Being able to mmap an export dma-buf buffer object has 2 main use-cases:
>
>     No special interfaces, userspace simply calls mmap on the dma-buf fd.
>
> +   Also, the userspace might need some sort of cache coherency management e.g.
> +   when CPU and GPU domains are being accessed through dma-buf at the same
> +   time. To circumvent this problem there are begin/end coherency markers, that
> +   forward directly to existing dma-buf device drivers vfunc hooks. Userspace
> +   can make use of those markers through the DMA_BUF_IOCTL_SYNC ioctl. The
> +   sequence would be used like following:
> +     - mmap dma-buf fd
> +     - for each drawing/upload cycle in CPU 1. SYNC_START ioctl, 2. read/write
> +       to mmap area 3. SYNC_END ioctl. This can be repeated as often as you
> +       want (with the new data being consumed by the GPU or say scanout device)
> +     - munamp once you don't need the buffer any more
> +
>  2. Supporting existing mmap interfaces in importers
>
>     Similar to the motivation for kernel cpu access it is again important that
> diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
> index b2ac13b..9a298bd 100644
> --- a/drivers/dma-buf/dma-buf.c
> +++ b/drivers/dma-buf/dma-buf.c
> @@ -34,6 +34,8 @@
>  #include <linux/poll.h>
>  #include <linux/reservation.h>
>
> +#include <uapi/linux/dma-buf.h>
> +
>  static inline int is_dma_buf_file(struct file *);
>
>  struct dma_buf_list {
> @@ -251,11 +253,52 @@ out:
>         return events;
>  }
>
> +static long dma_buf_ioctl(struct file *file,
> +                         unsigned int cmd, unsigned long arg)
> +{
> +       struct dma_buf *dmabuf;
> +       struct dma_buf_sync sync;
> +       enum dma_data_direction direction;
> +
> +       dmabuf = file->private_data;
> +
> +       if (!is_dma_buf_file(file))
> +               return -EINVAL;
> +
> +       switch (cmd) {
> +       case DMA_BUF_IOCTL_SYNC:
> +               if (copy_from_user(&sync, (void __user *) arg, sizeof(sync)))
> +                       return -EFAULT;
> +
> +               if (sync.flags & DMA_BUF_SYNC_RW)
> +                       direction = DMA_BIDIRECTIONAL;
> +               else if (sync.flags & DMA_BUF_SYNC_READ)
> +                       direction = DMA_FROM_DEVICE;
> +               else if (sync.flags & DMA_BUF_SYNC_WRITE)
> +                       direction = DMA_TO_DEVICE;
> +               else
> +                       return -EINVAL;
> +
> +               if (sync.flags & ~DMA_BUF_SYNC_VALID_FLAGS_MASK)
> +                       return -EINVAL;
> +
> +               if (sync.flags & DMA_BUF_SYNC_END)
> +                       dma_buf_end_cpu_access(dmabuf, direction);
> +               else
> +                       dma_buf_begin_cpu_access(dmabuf, direction);
> +
> +               return 0;
> +       default:
> +               return -ENOTTY;
> +       }
> +}
> +
>  static const struct file_operations dma_buf_fops = {
>         .release        = dma_buf_release,
>         .mmap           = dma_buf_mmap_internal,
>         .llseek         = dma_buf_llseek,
>         .poll           = dma_buf_poll,
> +       .unlocked_ioctl = dma_buf_ioctl,
>  };
>
>  /*
> diff --git a/include/uapi/linux/dma-buf.h b/include/uapi/linux/dma-buf.h
> new file mode 100644
> index 0000000..262f7a7
> --- /dev/null
> +++ b/include/uapi/linux/dma-buf.h
> @@ -0,0 +1,41 @@
> +/*
> + * Framework for buffer objects that can be shared across devices/subsystems.
> + *
> + * Copyright(C) 2015 Intel Ltd
> + *
> + * This program is free software; you can redistribute it and/or modify it
> + * under the terms of the GNU General Public License version 2 as published by
> + * the Free Software Foundation.
> + *
> + * This program is distributed in the hope that it will be useful, but WITHOUT
> + * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
> + * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
> + * more details.
> + *
> + * You should have received a copy of the GNU General Public License along with
> + * this program.  If not, see <http://www.gnu.org/licenses/>.
> + */
> +
> +#ifndef _DMA_BUF_UAPI_H_
> +#define _DMA_BUF_UAPI_H_
> +
> +enum dma_buf_sync_flags {
> +       DMA_BUF_SYNC_READ = (1 << 0),
> +       DMA_BUF_SYNC_WRITE = (2 << 0),
> +       DMA_BUF_SYNC_RW = (3 << 0),
> +       DMA_BUF_SYNC_START = (0 << 2),
> +       DMA_BUF_SYNC_END = (1 << 2),
> +
> +       DMA_BUF_SYNC_VALID_FLAGS_MASK = DMA_BUF_SYNC_RW |
> +               DMA_BUF_SYNC_END
> +};
> +
> +/* begin/end dma-buf functions used for userspace mmap. */
> +struct dma_buf_sync {
> +       enum dma_buf_sync_flags flags;
> +};
> +
> +#define DMA_BUF_BASE           'b'

'b' is occupied by vme and qat driver;
https://github.com/torvalds/linux/blob/master/Documentation/ioctl/ioctl-number.txt#L201

is it bad idea for drm.h to include these definition?
http://lxr.free-electrons.com/source/include/uapi/drm/drm.h#L684

Br, DS

> +#define DMA_BUF_IOCTL_SYNC     _IOW(DMA_BUF_BASE, 0, struct dma_buf_sync)
> +
> +#endif
> --
> 2.1.0
>
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