From: Daniel Vetter daniel.vetter@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) - munmap 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. v6 (Tiago): use __u64 structured padded flags instead enum. Adjust documentation about the recommendation on using sync ioctls.
Cc: Sumit Semwal sumit.semwal@linaro.org Signed-off-by: Daniel Vetter daniel.vetter@intel.com Signed-off-by: Tiago Vignatti tiago.vignatti@intel.com --- Documentation/dma-buf-sharing.txt | 22 +++++++++++++++++++- drivers/dma-buf/dma-buf.c | 43 +++++++++++++++++++++++++++++++++++++++ include/uapi/linux/dma-buf.h | 38 ++++++++++++++++++++++++++++++++++ 3 files changed, 102 insertions(+), 1 deletion(-) 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..2ddd4b2 100644 --- a/Documentation/dma-buf-sharing.txt +++ b/Documentation/dma-buf-sharing.txt @@ -350,7 +350,27 @@ Being able to mmap an export dma-buf buffer object has 2 main use-cases: handles, too). So it's beneficial to support this in a similar fashion on dma-buf to have a good transition path for existing Android userspace.
- No special interfaces, userspace simply calls mmap on the dma-buf fd. + No special interfaces, userspace simply calls mmap on the dma-buf fd. Very + important to note though is that, even if it is not mandatory, the userspace + is strongly recommended to always use the cache synchronization ioctl + (DMA_BUF_IOCTL_SYNC) discussed next. + + Some systems 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) + - munmap once you don't need the buffer any more + + In principle systems with the memory cache shared by the GPU and CPU may + not need SYNC_START and SYNC_END but still, userspace is always encouraged + to use these ioctls before and after, respectively, when accessing the + mapped address.
2. Supporting existing mmap interfaces in importers
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..bd195f2 --- /dev/null +++ b/include/uapi/linux/dma-buf.h @@ -0,0 +1,38 @@ +/* + * 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_ + +/* begin/end dma-buf functions used for userspace mmap. */ +struct dma_buf_sync { + __u64 flags; +}; + +#define DMA_BUF_SYNC_READ (1 << 0) +#define DMA_BUF_SYNC_WRITE (2 << 0) +#define DMA_BUF_SYNC_RW (3 << 0) +#define DMA_BUF_SYNC_START (0 << 2) +#define DMA_BUF_SYNC_END (1 << 2) +#define DMA_BUF_SYNC_VALID_FLAGS_MASK \ + (DMA_BUF_SYNC_RW | DMA_BUF_SYNC_END) + +#define DMA_BUF_BASE 'b' +#define DMA_BUF_IOCTL_SYNC _IOW(DMA_BUF_BASE, 0, struct dma_buf_sync) + +#endif