[RFC 9/9] drm/i915: Add sync framework support to execbuff IOCTL

John.C.Harrison
2015-07-17T14:31:45Z

From: John Harrison <John.C.Harrison@Intel.com>

Various projects desire a mechanism for managing dependencies between
work items asynchronously. This can also include work items across
complete different and independent systems. For example, an
application wants to retreive a frame from a video in device,
using it for rendering on a GPU then send it to the video out device
for display all without having to stall waiting for completion along
the way. The sync framework allows this. It encapsulates
synchronisation events in file descriptors. The application can
request a sync point for the completion of each piece of work. Drivers
should also take sync points in with each new work request and not
schedule the work to start until the sync has been signalled.

This patch adds sync framework support to the exec buffer IOCTL. A
sync point can be passed in to stall execution of the batch buffer
until signalled. And a sync point can be returned after each batch
buffer submission which will be signalled upon that batch buffer's
completion.

At present, the input sync point is simply waited on synchronously
inside the exec buffer IOCTL call. Once the GPU scheduler arrives,
this will be handled asynchronously inside the scheduler and the IOCTL
can return without having to wait.

Note also that the scheduler will re-order the execution of batch
buffers, e.g. because a batch buffer is stalled on a sync point and
cannot be submitted yet but other, independent, batch buffers are
being presented to the driver. This means that the timeline within the
sync points returned cannot be global to the engine. Instead they must
be kept per context per engine (the scheduler may not re-order batches
within a context). Hence the timeline cannot be based on the existing
seqno values but must be a new implementation.

This patch is a port of work by several people that has been pulled
across from Android. It has been updated several times across several
patches. Rather than attempt to port each individual patch, this
version is the finished product as a single patch. The various
contributors/authors along the way (in addition to myself) were:
Satyanantha RamaGopal M <rama.gopal.m.satyanantha@intel.com>
Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Michel Thierry <michel.thierry@intel.com>
Arun Siluvery <arun.siluvery@linux.intel.com>

[new patch in series]

For: VIZ-5190
Signed-off-by: John Harrison <John.C.Harrison@Intel.com>
---
drivers/gpu/drm/i915/i915_drv.h | 6 ++
drivers/gpu/drm/i915/i915_gem.c | 84 ++++++++++++++++++++++++++++
drivers/gpu/drm/i915/i915_gem_execbuffer.c | 90 ++++++++++++++++++++++++++++--
include/uapi/drm/i915_drm.h | 16 +++++-
4 files changed, 188 insertions(+), 8 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index d7f1aa5..cf6b7cd 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -2168,6 +2168,7 @@ struct drm_i915_gem_request {
struct list_head delay_free_list;
bool cancelled;
bool irq_enabled;
+ bool fence_external;

/** On Which ring this request was generated */
struct drm_i915_private *i915;
@@ -2252,6 +2253,11 @@ void i915_gem_request_notify(struct intel_engine_cs *ring);
int i915_create_fence_timeline(struct drm_device *dev,
struct intel_context *ctx,
struct intel_engine_cs *ring);
+#ifdef CONFIG_SYNC
+struct sync_fence;
+int i915_create_sync_fence(struct drm_i915_gem_request *req, int *fence_fd);
+bool i915_safe_to_ignore_fence(struct intel_engine_cs *ring, struct sync_fence *fence);
+#endif

static inline bool i915_gem_request_completed(struct drm_i915_gem_request *req)
{
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 3f20087..de93422 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -37,6 +37,9 @@
#include <linux/swap.h>
#include <linux/pci.h>
#include <linux/dma-buf.h>
+#ifdef CONFIG_SYNC
+#include <../drivers/staging/android/sync.h>
+#endif

#define RQ_BUG_ON(expr)

@@ -2549,6 +2552,15 @@ void __i915_add_request(struct drm_i915_gem_request *request,
*/
i915_gem_request_submit(request);

+ /*
+ * If an external sync point has been requested for this request then
+ * it can be waited on without the driver's knowledge, i.e. without
+ * calling __i915_wait_request(). Thus interrupts must be enabled
+ * from the start rather than only on demand.
+ */
+ if (request->fence_external)
+ i915_gem_request_enable_interrupt(request);
+
if (i915.enable_execlists)
ret = ring->emit_request(request);
else {
@@ -2857,6 +2869,78 @@ static uint32_t i915_fence_timeline_get_next_seqno(struct i915_fence_timeline *t
return seqno;
}

+#ifdef CONFIG_SYNC
+int i915_create_sync_fence(struct drm_i915_gem_request *req, int *fence_fd)
+{
+ char ring_name[] = "i915_ring0";
+ struct sync_fence *sync_fence;
+ int fd;
+
+ fd = get_unused_fd_flags(O_CLOEXEC);
+ if (fd < 0) {
+ DRM_DEBUG("No available file descriptors!\n");
+ *fence_fd = -1;
+ return fd;
+ }
+
+ ring_name[9] += req->ring->id;
+ sync_fence = sync_fence_create_dma(ring_name, &req->fence);
+ if (!sync_fence) {
+ put_unused_fd(fd);
+ *fence_fd = -1;
+ return -ENOMEM;
+ }
+
+ sync_fence_install(sync_fence, fd);
+ *fence_fd = fd;
+
+ // Necessary??? Who does the put???
+ fence_get(&req->fence);
+
+ req->fence_external = true;
+
+ return 0;
+}
+
+bool i915_safe_to_ignore_fence(struct intel_engine_cs *ring, struct sync_fence *sync_fence)
+{
+ struct fence *dma_fence;
+ struct drm_i915_gem_request *req;
+ bool ignore;
+ int i;
+
+ if (atomic_read(&sync_fence->status) != 0)
+ return true;
+
+ ignore = true;
+ for(i = 0; i < sync_fence->num_fences; i++) {
+ dma_fence = sync_fence->cbs[i].sync_pt;
+
+ /* No need to worry about dead points: */
+ if (fence_is_signaled(dma_fence))
+ continue;
+
+ /* Can't ignore other people's points: */
+ if(dma_fence->ops != &i915_gem_request_fops) {
+ ignore = false;
+ break;
+ }
+
+ req = container_of(dma_fence, typeof(*req), fence);
+
+ /* Can't ignore points on other rings: */
+ if (req->ring != ring) {
+ ignore = false;
+ break;
+ }
+
+ /* Same ring means guaranteed to be in order so ignore it. */
+ }
+
+ return ignore;
+}
+#endif
+
int i915_gem_request_alloc(struct intel_engine_cs *ring,
struct intel_context *ctx,
struct drm_i915_gem_request **req_out)
diff --git a/drivers/gpu/drm/i915/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
index 923a3c4..b1a1659 100644
--- a/drivers/gpu/drm/i915/i915_gem_execbuffer.c
+++ b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
@@ -26,6 +26,7 @@
*
*/

+#include <linux/syscalls.h>
#include <drm/drmP.h>
#include <drm/i915_drm.h>
#include "i915_drv.h"
@@ -33,6 +34,9 @@
#include "intel_drv.h"
#include <linux/dma_remapping.h>
#include <linux/uaccess.h>
+#ifdef CONFIG_SYNC
+#include <../drivers/staging/android/sync.h>
+#endif

#define __EXEC_OBJECT_HAS_PIN (1<<31)
#define __EXEC_OBJECT_HAS_FENCE (1<<30)
@@ -1403,6 +1407,35 @@ eb_get_batch(struct eb_vmas *eb)
return vma->obj;
}

+#ifdef CONFIG_SYNC
+static int i915_early_fence_wait(struct intel_engine_cs *ring, int fence_fd)
+{
+ struct sync_fence *fence;
+ int ret = 0;
+
+ if (fence_fd < 0) {
+ DRM_ERROR("Invalid wait fence fd %d on ring %d\n", fence_fd,
+ (int) ring->id);
+ return 1;
+ }
+
+ fence = sync_fence_fdget(fence_fd);
+ if (fence == NULL) {
+ DRM_ERROR("Invalid wait fence %d on ring %d\n", fence_fd,
+ (int) ring->id);
+ return 1;
+ }
+
+ if (atomic_read(&fence->status) == 0) {
+ if (!i915_safe_to_ignore_fence(ring, fence))
+ ret = sync_fence_wait(fence, 1000);
+ }
+
+ sync_fence_put(fence);
+ return ret;
+}
+#endif
+
static int
i915_gem_do_execbuffer(struct drm_device *dev, void *data,
struct drm_file *file,
@@ -1422,6 +1455,18 @@ i915_gem_do_execbuffer(struct drm_device *dev, void *data,
u32 dispatch_flags;
int ret;
bool need_relocs;
+ int fd_fence_complete = -1;
+#ifdef CONFIG_SYNC
+ int fd_fence_wait = lower_32_bits(args->rsvd2);
+#endif
+
+ /*
+ * Make sure an broken fence handle is not returned no matter
+ * how early an error might be hit. Note that rsvd2 has to be
+ * saved away first because it is also an input parameter!
+ */
+ if (args->flags & I915_EXEC_CREATE_FENCE)
+ args->rsvd2 = (__u64) -1;

if (!i915_gem_check_execbuffer(args))
return -EINVAL;
@@ -1505,6 +1550,19 @@ i915_gem_do_execbuffer(struct drm_device *dev, void *data,
dispatch_flags |= I915_DISPATCH_RS;
}

+#ifdef CONFIG_SYNC
+ /*
+ * Without a GPU scheduler, any fence waits must be done up front.
+ */
+ if (args->flags & I915_EXEC_WAIT_FENCE) {
+ ret = i915_early_fence_wait(ring, fd_fence_wait);
+ if (ret < 0)
+ return ret;
+
+ args->flags &= ~I915_EXEC_WAIT_FENCE;
+ }
+#endif
+
intel_runtime_pm_get(dev_priv);

ret = i915_mutex_lock_interruptible(dev);
@@ -1652,6 +1710,27 @@ i915_gem_do_execbuffer(struct drm_device *dev, void *data,
params->batch_obj = batch_obj;
params->ctx = ctx;

+#ifdef CONFIG_SYNC
+ if (args->flags & I915_EXEC_CREATE_FENCE) {
+ /*
+ * Caller has requested a sync fence.
+ * User interrupts will be enabled to make sure that
+ * the timeline is signalled on completion.
+ */
+ ret = i915_create_sync_fence(params->request,
+ &fd_fence_complete);
+ if (ret) {
+ DRM_ERROR("Fence creation failed for ring %d, ctx %p\n",
+ ring->id, ctx);
+ args->rsvd2 = (__u64) -1;
+ goto err;
+ }
+
+ /* Return the fence through the rsvd2 field */
+ args->rsvd2 = (__u64) fd_fence_complete;
+ }
+#endif
+
ret = dev_priv->gt.execbuf_submit(params, args, &eb->vmas);

err_batch_unpin:
@@ -1683,6 +1762,12 @@ pre_mutex_err:
/* intel_gpu_busy should also get a ref, so it will free when the device
* is really idle. */
intel_runtime_pm_put(dev_priv);
+
+ if (fd_fence_complete != -1) {
+ sys_close(fd_fence_complete);
+ args->rsvd2 = (__u64) -1;
+ }
+
return ret;
}

@@ -1788,11 +1873,6 @@ i915_gem_execbuffer2(struct drm_device *dev, void *data,
return -EINVAL;
}

- if (args->rsvd2 != 0) {
- DRM_DEBUG("dirty rvsd2 field\n");
- return -EINVAL;
- }
-
exec2_list = kmalloc(sizeof(*exec2_list)*args->buffer_count,
GFP_TEMPORARY | __GFP_NOWARN | __GFP_NORETRY);
if (exec2_list == NULL)
diff --git a/include/uapi/drm/i915_drm.h b/include/uapi/drm/i915_drm.h
index 192027b..9dbf67e 100644
--- a/include/uapi/drm/i915_drm.h
+++ b/include/uapi/drm/i915_drm.h
@@ -250,7 +250,7 @@ typedef struct _drm_i915_sarea {
#define DRM_IOCTL_I915_HWS_ADDR DRM_IOW(DRM_COMMAND_BASE + DRM_I915_HWS_ADDR, struct drm_i915_gem_init)
#define DRM_IOCTL_I915_GEM_INIT DRM_IOW(DRM_COMMAND_BASE + DRM_I915_GEM_INIT, struct drm_i915_gem_init)
#define DRM_IOCTL_I915_GEM_EXECBUFFER DRM_IOW(DRM_COMMAND_BASE + DRM_I915_GEM_EXECBUFFER, struct drm_i915_gem_execbuffer)
-#define DRM_IOCTL_I915_GEM_EXECBUFFER2 DRM_IOW(DRM_COMMAND_BASE + DRM_I915_GEM_EXECBUFFER2, struct drm_i915_gem_execbuffer2)
+#define DRM_IOCTL_I915_GEM_EXECBUFFER2 DRM_IOWR(DRM_COMMAND_BASE + DRM_I915_GEM_EXECBUFFER2, struct drm_i915_gem_execbuffer2)
#define DRM_IOCTL_I915_GEM_PIN DRM_IOWR(DRM_COMMAND_BASE + DRM_I915_GEM_PIN, struct drm_i915_gem_pin)
#define DRM_IOCTL_I915_GEM_UNPIN DRM_IOW(DRM_COMMAND_BASE + DRM_I915_GEM_UNPIN, struct drm_i915_gem_unpin)
#define DRM_IOCTL_I915_GEM_BUSY DRM_IOWR(DRM_COMMAND_BASE + DRM_I915_GEM_BUSY, struct drm_i915_gem_busy)
@@ -694,7 +694,7 @@ struct drm_i915_gem_exec_object2 {
__u64 flags;

__u64 rsvd1;
- __u64 rsvd2;
+ __u64 rsvd2; /* Used for fence fd */
};

struct drm_i915_gem_execbuffer2 {
@@ -775,7 +775,17 @@ struct drm_i915_gem_execbuffer2 {
*/
#define I915_EXEC_RESOURCE_STREAMER (1<<15)

-#define __I915_EXEC_UNKNOWN_FLAGS -(I915_EXEC_RESOURCE_STREAMER<<1)
+/** Caller supplies a sync fence fd in the rsvd2 field.
+ * Wait for it to be signalled before starting the work
+ */
+#define I915_EXEC_WAIT_FENCE (1<<16)
+
+/** Caller wants a sync fence fd for this execbuffer.
+ * It will be returned in rsvd2
+ */
+#define I915_EXEC_CREATE_FENCE (1<<17)
+
+#define __I915_EXEC_UNKNOWN_FLAGS -(I915_EXEC_CREATE_FENCE<<1)

#define I915_EXEC_CONTEXT_ID_MASK (0xffffffff)
#define i915_execbuffer2_set_context_id(eb2, context) \
--
1.9.1