[Linaro-mm-sig] Re: [PATCH 1/2] dma-buf: add dma_fence_unwrap

On Fri, Mar 11, 2022 at 12:02:43PM +0100, Christian König wrote:

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.

Signed-off-by: Christian König christian.koenig@amd.com

Documentation/driver-api/dma-buf.rst | 6 + drivers/dma-buf/Makefile | 1 + drivers/dma-buf/selftests.h | 1 + drivers/dma-buf/st-dma-fence-unwrap.c | 279 ++++++++++++++++++++++++++ include/linux/dma-fence-unwrap.h | 99 +++++++++ 5 files changed, 386 insertions(+) create mode 100644 drivers/dma-buf/st-dma-fence-unwrap.c create mode 100644 include/linux/dma-fence-unwrap.h

diff --git a/Documentation/driver-api/dma-buf.rst b/Documentation/driver-api/dma-buf.rst index 2cd7db82d9fe..7209500f08c8 100644 --- a/Documentation/driver-api/dma-buf.rst +++ b/Documentation/driver-api/dma-buf.rst @@ -194,6 +194,12 @@ DMA Fence Chain .. 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

diff --git a/drivers/dma-buf/Makefile b/drivers/dma-buf/Makefile
index 511805dbeb75..4c9eb53ba3f8 100644
--- a/drivers/dma-buf/Makefile
+++ b/drivers/dma-buf/Makefile
@@ -12,6 +12,7 @@ dmabuf_selftests-y := \
  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
diff --git a/drivers/dma-buf/selftests.h b/drivers/dma-buf/selftests.h
index 97d73aaa31da..851965867d9c 100644
--- a/drivers/dma-buf/selftests.h
+++ b/drivers/dma-buf/selftests.h
@@ -12,4 +12,5 @@
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)
diff --git a/drivers/dma-buf/st-dma-fence-unwrap.c b/drivers/dma-buf/st-dma-fence-unwrap.c
new file mode 100644
index 000000000000..d821faaebe93
--- /dev/null
+++ b/drivers/dma-buf/st-dma-fence-unwrap.c
@@ -0,0 +1,279 @@
+// 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 struct kmem_cache *slab_fences;

Your own slab feels a bit like overkill. kmalloc/kfree not good enough?

+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 void mock_fence_release(struct dma_fence *f) +{

• kmem_cache_free(slab_fences, to_mock_fence(f));

+}

+static const struct dma_fence_ops mock_ops = {

• .get_driver_name = mock_name,
• .get_timeline_name = mock_name,
• .release = mock_fence_release,

+};

+static struct dma_fence *mock_fence(void) +{

• struct mock_fence *f;
• f = kmem_cache_alloc(slab_fences, 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),
  

• };
• int ret;
• slab_fences = KMEM_CACHE(mock_fence,

• 		 SLAB_TYPESAFE_BY_RCU |
  

• 		 SLAB_HWCACHE_ALIGN);
  

• if (!slab_fences)

• return -ENOMEM;
  

• ret = subtests(tests, NULL);
• kmem_cache_destroy(slab_fences);
• return ret;

+} diff --git a/include/linux/dma-fence-unwrap.h b/include/linux/dma-fence-unwrap.h new file mode 100644 index 000000000000..54963df00c98 --- /dev/null +++ b/include/linux/dma-fence-unwrap.h @@ -0,0 +1,99 @@ +/* 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 christian.koenig@amd.com
• */

+#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

I think adding "This should be used together with dma_fence_unwrap_for_each() iterator macro." would be nice here. I just like links :-)

• */

+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;

+};

+/**

• • dma_fence_unwrap_array - helper to unwrap dma_fence_arrays
• • @cursor: cursor to initialize
• • Helper function to unwrap dma_fence_array containers, don't touch directly.
• • Use dma_fence_unwrap_first/next instead.
• */

+static inline struct dma_fence * +dma_fence_unwrap_array(struct dma_fence_unwrap * cursor)

Since this is a helper that no one should call I'd give it a __ prefix and drop the kerneldoc. Documenting stuff that people shouldn't use is confusing :-)

+{

• 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

I think it'd be really good to add a small paragraph to struct dma_fence_chain that this macro and iterator should be used for walking over all fences in a chain, including any fence arrays or anything like that.

With the bikesheds addressed:

Reviewed-by: Daniel Vetter daniel.vetter@ffwll.ch

-- 2.25.1