[RFC PATCH 02/29] dma-fence: Add dma_fence_user_fence

[Matthew Brost]

Normalize user fence attachment to a DMA fence. A user fence is a simple
seqno write to memory, implemented by attaching a DMA fence callback
that writes out the seqno. Intended use case is importing a dma-fence
into kernel and exporting a user fence.

Helpers added to allocate, attach, and free a dma_fence_user_fence.

Cc: Dave Airlie <airlied at redhat.com>
Cc: Simona Vetter <simona.vetter at ffwll.ch>
Cc: Christian Koenig <christian.koenig at amd.com>
Signed-off-by: Matthew Brost <matthew.brost at intel.com>
---
 drivers/dma-buf/Makefile               |  2 +-
 drivers/dma-buf/dma-fence-user-fence.c | 73 ++++++++++++++++++++++++++
 include/linux/dma-fence-user-fence.h   | 31 +++++++++++
 3 files changed, 105 insertions(+), 1 deletion(-)
 create mode 100644 drivers/dma-buf/dma-fence-user-fence.c
 create mode 100644 include/linux/dma-fence-user-fence.h

diff --git a/drivers/dma-buf/Makefile b/drivers/dma-buf/Makefile
index c25500bb38b5..ba9ba339319e 100644
--- a/drivers/dma-buf/Makefile
+++ b/drivers/dma-buf/Makefile
@@ -1,6 +1,6 @@
 # SPDX-License-Identifier: GPL-2.0-only
 obj-y := dma-buf.o dma-fence.o dma-fence-array.o dma-fence-chain.o \
-	 dma-fence-preempt.o dma-fence-unwrap.o dma-resv.o
+	 dma-fence-preempt.o dma-fence-unwrap.o dma-fence-user-fence.o dma-resv.o
 obj-$(CONFIG_DMABUF_HEAPS)	+= dma-heap.o
 obj-$(CONFIG_DMABUF_HEAPS)	+= heaps/
 obj-$(CONFIG_SYNC_FILE)		+= sync_file.o
diff --git a/drivers/dma-buf/dma-fence-user-fence.c b/drivers/dma-buf/dma-fence-user-fence.c
new file mode 100644
index 000000000000..5a4b289bacb8
--- /dev/null
+++ b/drivers/dma-buf/dma-fence-user-fence.c
@@ -0,0 +1,73 @@
+// SPDX-License-Identifier: MIT
+/*
+ * Copyright © 2024 Intel Corporation
+ */
+
+#include <linux/dma-fence-user-fence.h>
+#include <linux/slab.h>
+
+static void user_fence_cb(struct dma_fence *fence, struct dma_fence_cb *cb)
+{
+	struct dma_fence_user_fence *user_fence =
+		container_of(cb, struct dma_fence_user_fence, cb);
+
+	if (user_fence->map.is_iomem)
+		writeq(user_fence->seqno, user_fence->map.vaddr_iomem);
+	else
+		*(u64 *)user_fence->map.vaddr = user_fence->seqno;
+
+	dma_fence_user_fence_free(user_fence);
+}
+
+/**
+ * dma_fence_user_fence_alloc() - Allocate user fence
+ *
+ * Return: Allocated struct dma_fence_user_fence on Success, NULL on failure
+ */
+struct dma_fence_user_fence *dma_fence_user_fence_alloc(void)
+{
+	return kmalloc(sizeof(struct dma_fence_user_fence), GFP_KERNEL);
+}
+EXPORT_SYMBOL(dma_fence_user_fence_alloc);
+
+/**
+ * dma_fence_user_fence_free() - Free user fence
+ *
+ * Free user fence. Should only be called on a user fence if
+ * dma_fence_user_fence_attach is not called to cleanup original allocation from
+ * dma_fence_user_fence_alloc.
+ */
+void dma_fence_user_fence_free(struct dma_fence_user_fence *user_fence)
+{
+	kfree(user_fence);
+}
+EXPORT_SYMBOL(dma_fence_user_fence_free);
+
+/**
+ * dma_fence_user_fence_attach() - Attach user fence to dma-fence
+ *
+ * @fence: fence
+ * @user_fence user fence
+ * @map: IOSYS map to write seqno to
+ * @seqno: seqno to write to IOSYS map
+ *
+ * Attach a user fence, which is a seqno write to an IOSYS map, to a DMA fence.
+ * The caller must guarantee that the memory in the IOSYS map doesn't move
+ * before the fence signals. This is typically done by installing the DMA fence
+ * into the BO's DMA reservation bookkeeping slot from which the IOSYS was
+ * derived.
+ */
+void dma_fence_user_fence_attach(struct dma_fence *fence,
+				 struct dma_fence_user_fence *user_fence,
+				 struct iosys_map *map, u64 seqno)
+{
+	int err;
+
+	user_fence->map = *map;
+	user_fence->seqno = seqno;
+
+	err = dma_fence_add_callback(fence, &user_fence->cb, user_fence_cb);
+	if (err == -ENOENT)
+		user_fence_cb(NULL, &user_fence->cb);
+}
+EXPORT_SYMBOL(dma_fence_user_fence_attach);
diff --git a/include/linux/dma-fence-user-fence.h b/include/linux/dma-fence-user-fence.h
new file mode 100644
index 000000000000..8678129c7d56
--- /dev/null
+++ b/include/linux/dma-fence-user-fence.h
@@ -0,0 +1,31 @@
+/* SPDX-License-Identifier: MIT */
+/*
+ * Copyright © 2024 Intel Corporation
+ */
+
+#ifndef __LINUX_DMA_FENCE_USER_FENCE_H
+#define __LINUX_DMA_FENCE_USER_FENCE_H
+
+#include <linux/dma-fence.h>
+#include <linux/iosys-map.h>
+
+/** struct dma_fence_user_fence - User fence */
+struct dma_fence_user_fence {
+	/** @cb: dma-fence callback used to attach user fence to dma-fence */
+	struct dma_fence_cb cb;
+	/** @map: IOSYS map to write seqno to */
+	struct iosys_map map;
+	/** @seqno: seqno to write to IOSYS map */
+	u64 seqno;
+};
+
+struct dma_fence_user_fence *dma_fence_user_fence_alloc(void);
+
+void dma_fence_user_fence_free(struct dma_fence_user_fence *user_fence);
+
+void dma_fence_user_fence_attach(struct dma_fence *fence,
+				 struct dma_fence_user_fence *user_fence,
+				 struct iosys_map *map,
+				 u64 seqno);
+
+#endif
-- 
2.34.1