From: Daniel Vetter <daniel.vetter@xxxxxxxx>
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.
Cc: Sumit Semwal <sumit.semwal@xxxxxxxxxx>
Signed-off-by: Daniel Vetter <daniel.vetter@xxxxxxxxx>
Signed-off-by: Tiago Vignatti <tiago.vignatti@xxxxxxxxx>
---
Documentation/dma-buf-sharing.txt | 12 ++++++++++
drivers/dma-buf/dma-buf.c | 50 +++++++++++++++++++++++++++++++++++++++
include/uapi/linux/dma-buf.h | 43 +++++++++++++++++++++++++++++++++
3 files changed, 105 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 480c8de..2d8ee3b 100644
--- a/Documentation/dma-buf-sharing.txt
+++ b/Documentation/dma-buf-sharing.txt
@@ -355,6 +355,18 @@ 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 155c146..e628415 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 +253,59 @@ 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;
+
+ /* check for overflowing the buffer's size */
+ if (sync.start > dmabuf->size ||
+ sync.length > dmabuf->size - sync.start)
+ return -EINVAL;
+
+ if (sync.flags & DMA_BUF_SYNC_END)
+ dma_buf_end_cpu_access(dmabuf, sync.start,
+ sync.length, direction);
+ else
+ dma_buf_begin_cpu_access(dmabuf, sync.start,
+ sync.length, 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..902c9f6
--- /dev/null
+++ b/include/uapi/linux/dma-buf.h
@@ -0,0 +1,43 @@
+/*
+ * 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;
+ __u64 start;
+ __u64 length;
+};
+
+#define DMA_BUF_BASE 'b'
+#define DMA_BUF_IOCTL_SYNC _IOWR(DMA_BUF_BASE, 0, struct dma_buf_sync)
+
+#endif
--
2.1.0
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