dma-buf: add dma_fence_unwrap v2

Add a general purpose helper to deep dive into dma_fence_chain/dma_fence_array
structures and iterate over all the fences in them.

This is useful when we need to flatten out all fences in those structures.

v2: some selftests cleanup, improved function naming and documentation

Signed-off-by: Christian König <[e-mail]>
Reviewed-by: Daniel Vetter <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]

Documentation/driver-api/dma-buf.rst

···
 .. kernel-doc:: include/linux/dma-fence-chain.h
    :internal:
 
+DMA Fence unwrap
+~~~~~~~~~~~~~~~~
+
+.. kernel-doc:: include/linux/dma-fence-unwrap.h
+   :internal:
+
 DMA Fence uABI/Sync File
 ~~~~~~~~~~~~~~~~~~~~~~~~
 

drivers/dma-buf/Makefile

···
 	selftest.o \
 	st-dma-fence.o \
 	st-dma-fence-chain.o \
+	st-dma-fence-unwrap.o \
 	st-dma-resv.o
 
 obj-$(CONFIG_DMABUF_SELFTESTS)	+= dmabuf_selftests.o

drivers/dma-buf/selftests.h

···
 selftest(sanitycheck, __sanitycheck__) /* keep first (igt selfcheck) */
 selftest(dma_fence, dma_fence)
 selftest(dma_fence_chain, dma_fence_chain)
+selftest(dma_fence_unwrap, dma_fence_unwrap)
 selftest(dma_resv, dma_resv)

drivers/dma-buf/st-dma-fence-unwrap.c

···
+// SPDX-License-Identifier: MIT
+
+/*
+ * Copyright (C) 2022 Advanced Micro Devices, Inc.
+ */
+
+#include <linux/dma-fence-unwrap.h>
+#if 0
+#include <linux/kernel.h>
+#include <linux/kthread.h>
+#include <linux/mm.h>
+#include <linux/sched/signal.h>
+#include <linux/slab.h>
+#include <linux/spinlock.h>
+#include <linux/random.h>
+#endif
+
+#include "selftest.h"
+
+#define CHAIN_SZ (4 << 10)
+
+static inline struct mock_fence {
+	struct dma_fence base;
+	spinlock_t lock;
+} *to_mock_fence(struct dma_fence *f) {
+	return container_of(f, struct mock_fence, base);
+}
+
+static const char *mock_name(struct dma_fence *f)
+{
+	return "mock";
+}
+
+static const struct dma_fence_ops mock_ops = {
+	.get_driver_name = mock_name,
+	.get_timeline_name = mock_name,
+};
+
+static struct dma_fence *mock_fence(void)
+{
+	struct mock_fence *f;
+
+	f = kmalloc(sizeof(*f), GFP_KERNEL);
+	if (!f)
+		return NULL;
+
+	spin_lock_init(&f->lock);
+	dma_fence_init(&f->base, &mock_ops, &f->lock, 0, 0);
+
+	return &f->base;
+}
+
+static struct dma_fence *mock_array(unsigned int num_fences, ...)
+{
+	struct dma_fence_array *array;
+	struct dma_fence **fences;
+	va_list valist;
+	int i;
+
+	fences = kcalloc(num_fences, sizeof(*fences), GFP_KERNEL);
+	if (!fences)
+		return NULL;
+
+	va_start(valist, num_fences);
+	for (i = 0; i < num_fences; ++i)
+		fences[i] = va_arg(valist, typeof(*fences));
+	va_end(valist);
+
+	array = dma_fence_array_create(num_fences, fences,
+				       dma_fence_context_alloc(1),
+				       1, false);
+	if (!array)
+		goto cleanup;
+	return &array->base;
+
+cleanup:
+	for (i = 0; i < num_fences; ++i)
+		dma_fence_put(fences[i]);
+	kfree(fences);
+	return NULL;
+}
+
+static struct dma_fence *mock_chain(struct dma_fence *prev,
+				    struct dma_fence *fence)
+{
+	struct dma_fence_chain *f;
+
+	f = dma_fence_chain_alloc();
+	if (!f) {
+		dma_fence_put(prev);
+		dma_fence_put(fence);
+		return NULL;
+	}
+
+	dma_fence_chain_init(f, prev, fence, 1);
+	return &f->base;
+}
+
+static int sanitycheck(void *arg)
+{
+	struct dma_fence *f, *chain, *array;
+	int err = 0;
+
+	f = mock_fence();
+	if (!f)
+		return -ENOMEM;
+
+	array = mock_array(1, f);
+	if (!array)
+		return -ENOMEM;
+
+	chain = mock_chain(NULL, array);
+	if (!chain)
+		return -ENOMEM;
+
+	dma_fence_signal(f);
+	dma_fence_put(chain);
+	return err;
+}
+
+static int unwrap_array(void *arg)
+{
+	struct dma_fence *fence, *f1, *f2, *array;
+	struct dma_fence_unwrap iter;
+	int err = 0;
+
+	f1 = mock_fence();
+	if (!f1)
+		return -ENOMEM;
+
+	f2 = mock_fence();
+	if (!f2) {
+		dma_fence_put(f1);
+		return -ENOMEM;
+	}
+
+	array = mock_array(2, f1, f2);
+	if (!array)
+		return -ENOMEM;
+
+	dma_fence_unwrap_for_each(fence, &iter, array) {
+		if (fence == f1) {
+			f1 = NULL;
+		} else if (fence == f2) {
+			f2 = NULL;
+		} else {
+			pr_err("Unexpected fence!\n");
+			err = -EINVAL;
+		}
+	}
+
+	if (f1 || f2) {
+		pr_err("Not all fences seen!\n");
+		err = -EINVAL;
+	}
+
+	dma_fence_signal(f1);
+	dma_fence_signal(f2);
+	dma_fence_put(array);
+	return 0;
+}
+
+static int unwrap_chain(void *arg)
+{
+	struct dma_fence *fence, *f1, *f2, *chain;
+	struct dma_fence_unwrap iter;
+	int err = 0;
+
+	f1 = mock_fence();
+	if (!f1)
+		return -ENOMEM;
+
+	f2 = mock_fence();
+	if (!f2) {
+		dma_fence_put(f1);
+		return -ENOMEM;
+	}
+
+	chain = mock_chain(f1, f2);
+	if (!chain)
+		return -ENOMEM;
+
+	dma_fence_unwrap_for_each(fence, &iter, chain) {
+		if (fence == f1) {
+			f1 = NULL;
+		} else if (fence == f2) {
+			f2 = NULL;
+		} else {
+			pr_err("Unexpected fence!\n");
+			err = -EINVAL;
+		}
+	}
+
+	if (f1 || f2) {
+		pr_err("Not all fences seen!\n");
+		err = -EINVAL;
+	}
+
+	dma_fence_signal(f1);
+	dma_fence_signal(f2);
+	dma_fence_put(chain);
+	return 0;
+}
+
+static int unwrap_chain_array(void *arg)
+{
+	struct dma_fence *fence, *f1, *f2, *array, *chain;
+	struct dma_fence_unwrap iter;
+	int err = 0;
+
+	f1 = mock_fence();
+	if (!f1)
+		return -ENOMEM;
+
+	f2 = mock_fence();
+	if (!f2) {
+		dma_fence_put(f1);
+		return -ENOMEM;
+	}
+
+	array = mock_array(2, f1, f2);
+	if (!array)
+		return -ENOMEM;
+
+	chain = mock_chain(NULL, array);
+	if (!chain)
+		return -ENOMEM;
+
+	dma_fence_unwrap_for_each(fence, &iter, chain) {
+		if (fence == f1) {
+			f1 = NULL;
+		} else if (fence == f2) {
+			f2 = NULL;
+		} else {
+			pr_err("Unexpected fence!\n");
+			err = -EINVAL;
+		}
+	}
+
+	if (f1 || f2) {
+		pr_err("Not all fences seen!\n");
+		err = -EINVAL;
+	}
+
+	dma_fence_signal(f1);
+	dma_fence_signal(f2);
+	dma_fence_put(chain);
+	return 0;
+}
+
+int dma_fence_unwrap(void)
+{
+	static const struct subtest tests[] = {
+		SUBTEST(sanitycheck),
+		SUBTEST(unwrap_array),
+		SUBTEST(unwrap_chain),
+		SUBTEST(unwrap_chain_array),
+	};
+
+	return subtests(tests, NULL);
+}

include/linux/dma-fence-array.h

···
  *
  * Test if @array is a dma_fence_array object and if yes iterate over all fences
  * in the array. If not just iterate over the fence in @array itself.
+ *
+ * For a deep dive iterator see dma_fence_unwrap_for_each().
  */
 #define dma_fence_array_for_each(fence, index, head)			\
 	for (index = 0, fence = dma_fence_array_first(head); fence;	\

include/linux/dma-fence-chain.h

···
  *
  * Iterate over all fences in the chain. We keep a reference to the current
  * fence while inside the loop which must be dropped when breaking out.
+ *
+ * For a deep dive iterator see dma_fence_unwrap_for_each().
  */
 #define dma_fence_chain_for_each(iter, head)	\
 	for (iter = dma_fence_get(head); iter; \

include/linux/dma-fence-unwrap.h

···
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * fence-chain: chain fences together in a timeline
+ *
+ * Copyright (C) 2022 Advanced Micro Devices, Inc.
+ * Authors:
+ *	Christian König <[e-mail]>
+ */
+
+#ifndef __LINUX_DMA_FENCE_UNWRAP_H
+#define __LINUX_DMA_FENCE_UNWRAP_H
+
+#include <linux/dma-fence-chain.h>
+#include <linux/dma-fence-array.h>
+
+/**
+ * struct dma_fence_unwrap - cursor into the container structure
+ *
+ * Should be used with dma_fence_unwrap_for_each() iterator macro.
+ */
+struct dma_fence_unwrap {
+	/**
+	 * @chain: potential dma_fence_chain, but can be other fence as well
+	 */
+	struct dma_fence *chain;
+	/**
+	 * @array: potential dma_fence_array, but can be other fence as well
+	 */
+	struct dma_fence *array;
+	/**
+	 * @index: last returned index if @array is really a dma_fence_array
+	 */
+	unsigned int index;
+};
+
+/* Internal helper to start new array iteration, don't use directly */
+static inline struct dma_fence *
+__dma_fence_unwrap_array(struct dma_fence_unwrap * cursor)
+{
+	cursor->array = dma_fence_chain_contained(cursor->chain);
+	cursor->index = 0;
+	return dma_fence_array_first(cursor->array);
+}
+
+/**
+ * dma_fence_unwrap_first - return the first fence from fence containers
+ * @head: the entrypoint into the containers
+ * @cursor: current position inside the containers
+ *
+ * Unwraps potential dma_fence_chain/dma_fence_array containers and return the
+ * first fence.
+ */
+static inline struct dma_fence *
+dma_fence_unwrap_first(struct dma_fence *head, struct dma_fence_unwrap *cursor)
+{
+	cursor->chain = dma_fence_get(head);
+	return __dma_fence_unwrap_array(cursor);
+}
+
+/**
+ * dma_fence_unwrap_next - return the next fence from a fence containers
+ * @cursor: current position inside the containers
+ *
+ * Continue unwrapping the dma_fence_chain/dma_fence_array containers and return
+ * the next fence from them.
+ */
+static inline struct dma_fence *
+dma_fence_unwrap_next(struct dma_fence_unwrap *cursor)
+{
+	struct dma_fence *tmp;
+
+	++cursor->index;
+	tmp = dma_fence_array_next(cursor->array, cursor->index);
+	if (tmp)
+		return tmp;
+
+	cursor->chain = dma_fence_chain_walk(cursor->chain);
+	return __dma_fence_unwrap_array(cursor);
+}
+
+/**
+ * dma_fence_unwrap_for_each - iterate over all fences in containers
+ * @fence: current fence
+ * @cursor: current position inside the containers
+ * @head: starting point for the iterator
+ *
+ * Unwrap dma_fence_chain and dma_fence_array containers and deep dive into all
+ * potential fences in them. If @head is just a normal fence only that one is
+ * returned.
+ */
+#define dma_fence_unwrap_for_each(fence, cursor, head)			\
+	for (fence = dma_fence_unwrap_first(head, cursor); fence;	\
+	     fence = dma_fence_unwrap_next(cursor))
+
+#endif