i965/sync: Implement fences based on Linux sync_file

This patch implements a new type of struct brw_fence, one that is based
struct sync_file.

This completes support for EGL_ANDROID_native_fence_sync.

* Background

  Linux 4.7 added a new file type, struct sync_file. See

    commit 460bfc41fd52959311ed0328163f785e023857af
    Author:  Gustavo Padovan <gustavo.padovan@collabora.co.uk>
    Date:    Thu Apr 28 10:46:57 2016 -0300
    Subject: dma-buf/sync_file: de-stage sync_file headers

  A sync file is a cross-driver explicit synchronization primitive. In a
  sense, sync_file's relation to synchronization is similar to dma_buf's
  relation to memory: both are primitives that can be imported and
  exported across drivers (at least in theory).

Reviewed-by: Rafael Antognolli <rafael.antognolli@intel.com>
Tested-by: Rafael Antognolli <rafael.antognolli@intel.com>
Acked-by: Kenneth Graunke <kenneth@whitecape.org>

src/mesa/drivers/dri/i965/brw_sync.c

@@ -38,6 +38,8 @@
  * performance bottleneck, though.
  */
 
+#include <libsync.h> /* Requires Android or libdrm-2.4.72 */
+
 #include "main/imports.h"
 
 #include "brw_context.h"
@@ -47,12 +49,20 @@ struct brw_fence {
    struct brw_context *brw;
 
    enum brw_fence_type {
+      /** The fence waits for completion of brw_fence::batch_bo. */
       BRW_FENCE_TYPE_BO_WAIT,
+
+      /** The fence waits for brw_fence::sync_fd to signal. */
+      BRW_FENCE_TYPE_SYNC_FD,
    } type;
 
-   /** The fence waits for completion of this batch. */
+   union {
       drm_intel_bo *batch_bo;
 
+      /* This struct owns the fd. */
+      int sync_fd;
+   };
+
    mtx_t mutex;
    bool signalled;
 };
@@ -74,6 +84,9 @@ brw_fence_init(struct brw_context *brw, struct brw_fence *fence,
    case BRW_FENCE_TYPE_BO_WAIT:
       fence->batch_bo = NULL;
       break;
+    case BRW_FENCE_TYPE_SYNC_FD:
+      fence->sync_fd = -1;
+      break;
    }
 }
 
@@ -85,6 +98,10 @@ brw_fence_finish(struct brw_fence *fence)
       if (fence->batch_bo)
          drm_intel_bo_unreference(fence->batch_bo);
       break;
+   case BRW_FENCE_TYPE_SYNC_FD:
+      if (fence->sync_fd != -1)
+         close(fence->sync_fd);
+      break;
    }
 
    mtx_destroy(&fence->mutex);
@@ -109,11 +126,46 @@ brw_fence_insert_locked(struct brw_context *brw, struct brw_fence *fence)
          return false;
       }
       break;
+   case BRW_FENCE_TYPE_SYNC_FD:
+      assert(!fence->signalled);
+
+      if (fence->sync_fd == -1) {
+         /* Create an out-fence that signals after all pending commands
+          * complete.
+          */
+         if (intel_batchbuffer_flush_fence(brw, -1, &fence->sync_fd) < 0)
+            return false;
+         assert(fence->sync_fd != -1);
+      } else {
+         /* Wait on the in-fence before executing any subsequently submitted
+          * commands.
+          */
+         if (intel_batchbuffer_flush(brw) < 0)
+            return false;
+
+         /* Emit a dummy batch just for the fence. */
+         brw_emit_mi_flush(brw);
+         if (intel_batchbuffer_flush_fence(brw, fence->sync_fd, NULL) < 0)
+            return false;
+      }
+      break;
    }
 
    return true;
 }
 
+static bool MUST_CHECK
+brw_fence_insert(struct brw_context *brw, struct brw_fence *fence)
+{
+   bool ret;
+
+   mtx_lock(&fence->mutex);
+   ret = brw_fence_insert_locked(brw, fence);
+   mtx_unlock(&fence->mutex);
+
+   return ret;
+}
+
 static bool
 brw_fence_has_completed_locked(struct brw_fence *fence)
 {
@@ -134,6 +186,16 @@ brw_fence_has_completed_locked(struct brw_fence *fence)
       fence->batch_bo = NULL;
       fence->signalled = true;
 
+      return true;
+
+   case BRW_FENCE_TYPE_SYNC_FD:
+      assert(fence->sync_fd != -1);
+
+      if (sync_wait(fence->sync_fd, 0) == -1)
+         return false;
+
+      fence->signalled = true;
+
       return true;
    }
 
@@ -156,6 +218,8 @@ static bool
 brw_fence_client_wait_locked(struct brw_context *brw, struct brw_fence *fence,
                              uint64_t timeout)
 {
+   int32_t timeout_i32;
+
    if (fence->signalled)
       return true;
 
@@ -181,6 +245,20 @@ brw_fence_client_wait_locked(struct brw_context *brw, struct brw_fence *fence,
       drm_intel_bo_unreference(fence->batch_bo);
       fence->batch_bo = NULL;
 
+      return true;
+   case BRW_FENCE_TYPE_SYNC_FD:
+      if (fence->sync_fd == -1)
+         return false;
+
+      if (timeout > INT32_MAX)
+         timeout_i32 = -1;
+      else
+         timeout_i32 = timeout;
+
+      if (sync_wait(fence->sync_fd, timeout_i32) == -1)
+         return false;
+
+      fence->signalled = true;
       return true;
    }
 
@@ -216,6 +294,16 @@ brw_fence_server_wait(struct brw_context *brw, struct brw_fence *fence)
        * the previous one is done.
        */
       break;
+   case BRW_FENCE_TYPE_SYNC_FD:
+      assert(fence->sync_fd != -1);
+
+      /* The user wants explicit synchronization, so give them what they want. */
+      if (!brw_fence_insert(brw, fence)) {
+         /* FIXME: There exists no way yet to report an error here. If an error
+          * occurs, continue silently and hope for the best.
+          */
+      }
+      break;
    }
 }
 
@@ -350,12 +438,80 @@ brw_dri_server_wait_sync(__DRIcontext *ctx, void *_fence, unsigned flags)
    brw_fence_server_wait(fence->brw, fence);
 }
 
+static unsigned
+brw_dri_get_capabilities(__DRIscreen *dri_screen)
+{
+   struct intel_screen *screen = dri_screen->driverPrivate;
+   unsigned caps = 0;
+
+   if (screen->has_exec_fence)
+      caps |=  __DRI_FENCE_CAP_NATIVE_FD;
+
+   return caps;
+}
+
+static void *
+brw_dri_create_fence_fd(__DRIcontext *dri_ctx, int fd)
+{
+   struct brw_context *brw = dri_ctx->driverPrivate;
+   struct brw_fence *fence;
+
+   assert(brw->screen->has_exec_fence);
+
+   fence = calloc(1, sizeof(*fence));
+   if (!fence)
+      return NULL;
+
+   brw_fence_init(brw, fence, BRW_FENCE_TYPE_SYNC_FD);
+
+   if (fd == -1) {
+      /* Create an out-fence fd */
+      if (!brw_fence_insert_locked(brw, fence))
+         goto fail;
+   } else {
+      /* Import the sync fd as an in-fence. */
+      fence->sync_fd = fd;
+   }
+
+   assert(fence->sync_fd != -1);
+
+   return fence;
+
+fail:
+   brw_fence_finish(fence);
+   free(fence);
+   return NULL;
+}
+
+static int
+brw_dri_get_fence_fd_locked(struct brw_fence *fence)
+{
+   assert(fence->type == BRW_FENCE_TYPE_SYNC_FD);
+   return dup(fence->sync_fd);
+}
+
+static int
+brw_dri_get_fence_fd(__DRIscreen *dri_screen, void *_fence)
+{
+   struct brw_fence *fence = _fence;
+   int fd;
+
+   mtx_lock(&fence->mutex);
+   fd = brw_dri_get_fence_fd_locked(fence);
+   mtx_unlock(&fence->mutex);
+
+   return fd;
+}
+
 const __DRI2fenceExtension intelFenceExtension = {
-   .base = { __DRI2_FENCE, 1 },
+   .base = { __DRI2_FENCE, 2 },
 
    .create_fence = brw_dri_create_fence,
    .destroy_fence = brw_dri_destroy_fence,
    .client_wait_sync = brw_dri_client_wait_sync,
    .server_wait_sync = brw_dri_server_wait_sync,
    .get_fence_from_cl_event = NULL,
+   .get_capabilities = brw_dri_get_capabilities,
+   .create_fence_fd = brw_dri_create_fence_fd,
+   .get_fence_fd = brw_dri_get_fence_fd,
 };