[PATCH 2/4] dma-buf: Add ioctls to allow userspace to flush

[Tiago Vignatti]

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.

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         | 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