dma-buf: Add ioctls to allow userspace to flush
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. v7 (Tiago): Alex' nit on flags definition and being even more wording in the doc about sync usage. v9 (Tiago): remove useless is_dma_buf_file check. Fix sync.flags conditionals and its mask order check. Add <linux/types.h> include in dma-buf.h. Cc: Ville Syrjälä <ville.syrjala@linux.intel.com> Cc: David Herrmann <dh.herrmann@gmail.com> Cc: Sumit Semwal <sumit.semwal@linaro.org> Reviewed-by: Stéphane Marchesin <marcheu@chromium.org> Signed-off-by: Daniel Vetter <daniel.vetter@intel.com> Signed-off-by: Tiago Vignatti <tiago.vignatti@intel.com> Reviewed-by: David Herrmann <dh.herrmann@gmail.com> Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch> Link: http://patchwork.freedesktop.org/patch/msgid/1455228291-29640-1-git-send-email-tiago.vignatti@intel.comhifive-unleashed-5.1
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@ -350,7 +350,26 @@ Being able to mmap an export dma-buf buffer object has 2 main use-cases:
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handles, too). So it's beneficial to support this in a similar fashion on
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handles, too). So it's beneficial to support this in a similar fashion on
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dma-buf to have a good transition path for existing Android userspace.
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dma-buf to have a good transition path for existing Android userspace.
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No special interfaces, userspace simply calls mmap on the dma-buf fd.
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No special interfaces, userspace simply calls mmap on the dma-buf fd, making
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sure that the cache synchronization ioctl (DMA_BUF_IOCTL_SYNC) is *always*
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used when the access happens. This is discussed next paragraphs.
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Some systems might need some sort of cache coherency management e.g. when
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CPU and GPU domains are being accessed through dma-buf at the same time. To
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circumvent this problem there are begin/end coherency markers, that forward
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directly to existing dma-buf device drivers vfunc hooks. Userspace can make
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use of those markers through the DMA_BUF_IOCTL_SYNC ioctl. The sequence
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would be used like following:
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- mmap dma-buf fd
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- for each drawing/upload cycle in CPU 1. SYNC_START ioctl, 2. read/write
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to mmap area 3. SYNC_END ioctl. This can be repeated as often as you
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want (with the new data being consumed by the GPU or say scanout device)
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- munmap once you don't need the buffer any more
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Therefore, for correctness and optimal performance, systems with the memory
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cache shared by the GPU and CPU i.e. the "coherent" and also the
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"incoherent" are always required to use SYNC_START and SYNC_END before and
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after, respectively, when accessing the mapped address.
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2. Supporting existing mmap interfaces in importers
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2. Supporting existing mmap interfaces in importers
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@ -34,6 +34,8 @@
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#include <linux/poll.h>
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#include <linux/poll.h>
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#include <linux/reservation.h>
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#include <linux/reservation.h>
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#include <uapi/linux/dma-buf.h>
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static inline int is_dma_buf_file(struct file *);
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static inline int is_dma_buf_file(struct file *);
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struct dma_buf_list {
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struct dma_buf_list {
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@ -251,11 +253,54 @@ out:
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return events;
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return events;
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}
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}
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static long dma_buf_ioctl(struct file *file,
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unsigned int cmd, unsigned long arg)
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{
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struct dma_buf *dmabuf;
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struct dma_buf_sync sync;
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enum dma_data_direction direction;
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dmabuf = file->private_data;
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switch (cmd) {
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case DMA_BUF_IOCTL_SYNC:
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if (copy_from_user(&sync, (void __user *) arg, sizeof(sync)))
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return -EFAULT;
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if (sync.flags & ~DMA_BUF_SYNC_VALID_FLAGS_MASK)
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return -EINVAL;
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switch (sync.flags & DMA_BUF_SYNC_RW) {
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case DMA_BUF_SYNC_READ:
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direction = DMA_FROM_DEVICE;
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break;
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case DMA_BUF_SYNC_WRITE:
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direction = DMA_TO_DEVICE;
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break;
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case DMA_BUF_SYNC_RW:
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direction = DMA_BIDIRECTIONAL;
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break;
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default:
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return -EINVAL;
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}
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if (sync.flags & DMA_BUF_SYNC_END)
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dma_buf_end_cpu_access(dmabuf, direction);
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else
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dma_buf_begin_cpu_access(dmabuf, direction);
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return 0;
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default:
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return -ENOTTY;
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}
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}
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static const struct file_operations dma_buf_fops = {
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static const struct file_operations dma_buf_fops = {
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.release = dma_buf_release,
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.release = dma_buf_release,
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.mmap = dma_buf_mmap_internal,
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.mmap = dma_buf_mmap_internal,
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.llseek = dma_buf_llseek,
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.llseek = dma_buf_llseek,
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.poll = dma_buf_poll,
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.poll = dma_buf_poll,
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.unlocked_ioctl = dma_buf_ioctl,
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};
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};
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/*
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/*
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@ -0,0 +1,40 @@
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/*
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* Framework for buffer objects that can be shared across devices/subsystems.
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*
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* Copyright(C) 2015 Intel Ltd
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*
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* This program is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License version 2 as published by
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* the Free Software Foundation.
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*
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* This program is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
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* more details.
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*
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* You should have received a copy of the GNU General Public License along with
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* this program. If not, see <http://www.gnu.org/licenses/>.
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*/
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#ifndef _DMA_BUF_UAPI_H_
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#define _DMA_BUF_UAPI_H_
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#include <linux/types.h>
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/* begin/end dma-buf functions used for userspace mmap. */
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struct dma_buf_sync {
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__u64 flags;
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};
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#define DMA_BUF_SYNC_READ (1 << 0)
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#define DMA_BUF_SYNC_WRITE (2 << 0)
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#define DMA_BUF_SYNC_RW (DMA_BUF_SYNC_READ | DMA_BUF_SYNC_WRITE)
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#define DMA_BUF_SYNC_START (0 << 2)
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#define DMA_BUF_SYNC_END (1 << 2)
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#define DMA_BUF_SYNC_VALID_FLAGS_MASK \
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(DMA_BUF_SYNC_RW | DMA_BUF_SYNC_END)
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#define DMA_BUF_BASE 'b'
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#define DMA_BUF_IOCTL_SYNC _IOW(DMA_BUF_BASE, 0, struct dma_buf_sync)
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#endif
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Reference in New Issue