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

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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@xxxxxxx>
> ---
>  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@xxxxxxx>
> + */
> +
> +#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@xxxxxxxx>

> -- 
> 2.25.1
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch



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