Re: [PATCH 2/3] dma-buf: heaps: add chunk heap to dmabuf heaps

[David Hildenbrand]

On 18.08.20 10:04, Hyesoo Yu wrote:
> This patch adds support for a chunk heap that allows for buffers
> that are made up of a list of fixed size chunks taken from a CMA.
> Chunk sizes are configuratd when the heaps are created.
> 
> Signed-off-by: Hyesoo Yu <hyesoo.yu@xxxxxxxxxxx>
> ---
>  drivers/dma-buf/heaps/Kconfig      |   9 ++
>  drivers/dma-buf/heaps/Makefile     |   1 +
>  drivers/dma-buf/heaps/chunk_heap.c | 222 +++++++++++++++++++++++++++++++++++++
>  3 files changed, 232 insertions(+)
>  create mode 100644 drivers/dma-buf/heaps/chunk_heap.c
> 
> diff --git a/drivers/dma-buf/heaps/Kconfig b/drivers/dma-buf/heaps/Kconfig
> index a5eef06..98552fa 100644
> --- a/drivers/dma-buf/heaps/Kconfig
> +++ b/drivers/dma-buf/heaps/Kconfig
> @@ -12,3 +12,12 @@ config DMABUF_HEAPS_CMA
>  	  Choose this option to enable dma-buf CMA heap. This heap is backed
>  	  by the Contiguous Memory Allocator (CMA). If your system has these
>  	  regions, you should say Y here.
> +
> +config DMABUF_HEAPS_CHUNK
> +	tristate "DMA-BUF CHUNK Heap"
> +	depends on DMABUF_HEAPS && DMA_CMA
> +	help
> +	  Choose this option to enable dma-buf CHUNK heap. This heap is backed
> +	  by the Contiguous Memory Allocator (CMA) and allocate the buffers that
> +	  are made up to a list of fixed size chunks tasken from CMA. Chunk sizes
> +	  are configurated when the heaps are created.
> diff --git a/drivers/dma-buf/heaps/Makefile b/drivers/dma-buf/heaps/Makefile
> index 6e54cde..3b2a0986 100644
> --- a/drivers/dma-buf/heaps/Makefile
> +++ b/drivers/dma-buf/heaps/Makefile
> @@ -2,3 +2,4 @@
>  obj-y					+= heap-helpers.o
>  obj-$(CONFIG_DMABUF_HEAPS_SYSTEM)	+= system_heap.o
>  obj-$(CONFIG_DMABUF_HEAPS_CMA)		+= cma_heap.o
> +obj-$(CONFIG_DMABUF_HEAPS_CHUNK)	+= chunk_heap.o
> diff --git a/drivers/dma-buf/heaps/chunk_heap.c b/drivers/dma-buf/heaps/chunk_heap.c
> new file mode 100644
> index 0000000..1eefaec
> --- /dev/null
> +++ b/drivers/dma-buf/heaps/chunk_heap.c
> @@ -0,0 +1,222 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * ION Memory Allocator chunk heap exporter
> + *
> + * Copyright (c) 2020 Samsung Electronics Co., Ltd.
> + * Author: <hyesoo.yu@xxxxxxxxxxx> for Samsung Electronics.
> + */
> +
> +#include <linux/platform_device.h>
> +#include <linux/cma.h>
> +#include <linux/device.h>
> +#include <linux/dma-buf.h>
> +#include <linux/dma-heap.h>
> +#include <linux/dma-contiguous.h>
> +#include <linux/err.h>
> +#include <linux/errno.h>
> +#include <linux/highmem.h>
> +#include <linux/module.h>
> +#include <linux/slab.h>
> +#include <linux/scatterlist.h>
> +#include <linux/sched/signal.h>
> +#include <linux/of_reserved_mem.h>
> +#include <linux/of.h>
> +
> +#include "heap-helpers.h"
> +
> +struct chunk_heap {
> +	struct dma_heap *heap;
> +	phys_addr_t base;
> +	phys_addr_t size;
> +	atomic_t cur_pageblock_idx;
> +	unsigned int max_num_pageblocks;
> +	unsigned int order;
> +};
> +
> +static void chunk_heap_free(struct heap_helper_buffer *buffer)
> +{
> +	struct chunk_heap *chunk_heap = dma_heap_get_drvdata(buffer->heap);
> +	pgoff_t pg;
> +
> +	for (pg = 0; pg < buffer->pagecount; pg++)
> +		__free_pages(buffer->pages[pg], chunk_heap->order);
> +	kvfree(buffer->pages);
> +	kfree(buffer);
> +}
> +
> +static inline unsigned long chunk_get_next_pfn(struct chunk_heap *chunk_heap)
> +{
> +	unsigned long i = atomic_inc_return(&chunk_heap->cur_pageblock_idx) %
> +		chunk_heap->max_num_pageblocks;
> +
> +	return PHYS_PFN(chunk_heap->base) + i * pageblock_nr_pages;
> +}
> +
> +static int chunk_alloc_pages(struct chunk_heap *chunk_heap, struct page **pages,
> +			     unsigned int order, unsigned int count)
> +{
> +	unsigned long base;
> +	unsigned int i = 0, nr_block = 0, nr_elem, ret;
> +
> +	while (count) {
> +		/*
> +		 * If the number of scanned page block is the same as max block,
> +		 * the tries of allocation fails.
> +		 */
> +		if (nr_block++ == chunk_heap->max_num_pageblocks) {
> +			ret = -ENOMEM;
> +			goto err_bulk;
> +		}
> +		base = chunk_get_next_pfn(chunk_heap);
> +		nr_elem = min_t(unsigned int, count, pageblock_nr_pages >> order);
> +		ret = alloc_pages_bulk(base, base + pageblock_nr_pages, MIGRATE_CMA,
> +				       GFP_KERNEL, order, nr_elem, pages + i);

So you are bypassing the complete cma allocator here. This all smells
like a complete hack to me. No, I don't think this is the right way to
support (or rather speed up allocations for) special, weird hardware.

-- 
Thanks,

David / dhildenb