[RFC][PATCH 1/2] dma-heap: Keep track of the heap device struct

[RFC][PATCH 1/2] dma-heap: Keep track of the heap device struct

[John Stultz]

Keep track of the heap device struct.

This will be useful for special DMA allocations
and actions.

Cc: Sumit Semwal <sumit.semwal@linaro.org>
Cc: Andrew F. Davis <afd@ti.com>
Cc: Benjamin Gaignard <benjamin.gaignard@linaro.org>
Cc: Liam Mark <lmark@codeaurora.org>
Cc: Laura Abbott <labbott@kernel.org>
Cc: Brian Starkey <Brian.Starkey@arm.com>
Cc: Hridya Valsaraju <hridya@google.com>
Cc: linux-media@vger.kernel.org
Cc: dri-devel@lists.freedesktop.org
Signed-off-by: John Stultz <john.stultz@linaro.org>
---
 drivers/dma-buf/dma-heap.c | 33 +++++++++++++++++++++++++--------
 include/linux/dma-heap.h   |  9 +++++++++
 2 files changed, 34 insertions(+), 8 deletions(-)

diff --git a/drivers/dma-buf/dma-heap.c b/drivers/dma-buf/dma-heap.c
index afd22c9dbdcf..72c746755d89 100644
--- a/drivers/dma-buf/dma-heap.c
+++ b/drivers/dma-buf/dma-heap.c
@@ -30,6 +30,7 @@
  * @heap_devt		heap device node
  * @list		list head connecting to list of heaps
  * @heap_cdev		heap char device
+ * @heap_dev		heap device struct
  *
  * Represents a heap of memory from which buffers can be made.
  */
@@ -40,6 +41,7 @@ struct dma_heap {
 	dev_t heap_devt;
 	struct list_head list;
 	struct cdev heap_cdev;
+	struct device *heap_dev;
 };
 
 static LIST_HEAD(heap_list);
@@ -190,10 +192,21 @@ void *dma_heap_get_drvdata(struct dma_heap *heap)
 	return heap->priv;
 }
 
+/**
+ * dma_heap_get_dev() - get device struct for the heap
+ * @heap: DMA-Heap to retrieve device struct from
+ *
+ * Returns:
+ * The device struct for the heap.
+ */
+struct device *dma_heap_get_dev(struct dma_heap *heap)
+{
+	return heap->heap_dev;
+}
+
 struct dma_heap *dma_heap_add(const struct dma_heap_export_info *exp_info)
 {
 	struct dma_heap *heap, *h, *err_ret;
-	struct device *dev_ret;
 	unsigned int minor;
 	int ret;
 
@@ -247,16 +260,20 @@ struct dma_heap *dma_heap_add(const struct dma_heap_export_info *exp_info)
 		goto err1;
 	}
 
-	dev_ret = device_create(dma_heap_class,
-				NULL,
-				heap->heap_devt,
-				NULL,
-				heap->name);
-	if (IS_ERR(dev_ret)) {
+	heap->heap_dev = device_create(dma_heap_class,
+				       NULL,
+				       heap->heap_devt,
+				       NULL,
+				       heap->name);
+	if (IS_ERR(heap->heap_dev)) {
 		pr_err("dma_heap: Unable to create device\n");
-		err_ret = ERR_CAST(dev_ret);
+		err_ret = ERR_CAST(heap->heap_dev);
 		goto err2;
 	}
+
+	/* Make sure it doesn't disappear on us */
+	heap->heap_dev = get_device(heap->heap_dev);
+
 	/* Add heap to the list */
 	mutex_lock(&heap_list_lock);
 	list_add(&heap->list, &heap_list);
diff --git a/include/linux/dma-heap.h b/include/linux/dma-heap.h
index 454e354d1ffb..82857e096910 100644
--- a/include/linux/dma-heap.h
+++ b/include/linux/dma-heap.h
@@ -50,6 +50,15 @@ struct dma_heap_export_info {
  */
 void *dma_heap_get_drvdata(struct dma_heap *heap);
 
+/**
+ * dma_heap_get_dev() - get device struct for the heap
+ * @heap: DMA-Heap to retrieve device struct from
+ *
+ * Returns:
+ * The device struct for the heap.
+ */
+struct device *dma_heap_get_dev(struct dma_heap *heap);
+
 /**
  * dma_heap_add - adds a heap to dmabuf heaps
  * @exp_info:		information needed to register this heap
-- 
2.17.1

[RFC][PATCH 2/2] dma-heap: Add a system-uncached heap

[John Stultz]

This adds a heap that allocates non-contiguous buffers that are
marked as writecombined, so they are not cached by the CPU.

This is useful, as most graphics buffers are usually not touched
by the CPU or only written into once by the CPU. So when mapping
the buffer over and over between devices, we can skip the CPU
syncing, which saves a lot of cache management overhead, greatly
improving performance.

For folk using ION, there was a ION_FLAG_CACHED flag, which
signaled if the returned buffer should be CPU cacheable or not.
With DMA-BUF heaps, we have no such flag, and by default the
current heaps (system and cma) produce CPU cachable buffers.
So for folks transitioning from ION to DMA-BUF Heaps, this fills
in some of that missing functionality.

This does have a few "ugly" bits that were required to get
the buffer properly flushed out initially which I'd like to
improve. So feedback would be very welcome!

Many thanks to Liam Mark for his help to get this working.

Cc: Sumit Semwal <sumit.semwal@linaro.org>
Cc: Andrew F. Davis <afd@ti.com>
Cc: Benjamin Gaignard <benjamin.gaignard@linaro.org>
Cc: Liam Mark <lmark@codeaurora.org>
Cc: Laura Abbott <labbott@kernel.org>
Cc: Brian Starkey <Brian.Starkey@arm.com>
Cc: Hridya Valsaraju <hridya@google.com>
Cc: linux-media@vger.kernel.org
Cc: dri-devel@lists.freedesktop.org
Signed-off-by: John Stultz <john.stultz@linaro.org>
---
 drivers/dma-buf/heaps/Kconfig                |  10 +
 drivers/dma-buf/heaps/Makefile               |   1 +
 drivers/dma-buf/heaps/system_uncached_heap.c | 392 +++++++++++++++++++
 3 files changed, 403 insertions(+)
 create mode 100644 drivers/dma-buf/heaps/system_uncached_heap.c

diff --git a/drivers/dma-buf/heaps/Kconfig b/drivers/dma-buf/heaps/Kconfig
index a5eef06c4226..420b0ed0a512 100644
--- a/drivers/dma-buf/heaps/Kconfig
+++ b/drivers/dma-buf/heaps/Kconfig
@@ -5,6 +5,16 @@ config DMABUF_HEAPS_SYSTEM
 	  Choose this option to enable the system dmabuf heap. The system heap
 	  is backed by pages from the buddy allocator. If in doubt, say Y.
 
+config DMABUF_HEAPS_SYSTEM_UNCACHED
+	bool "DMA-BUF Uncached System Heap"
+	depends on DMABUF_HEAPS
+	help
+	  Choose this option to enable the uncached system dmabuf heap. This
+	  heap is backed by pages from the buddy allocator, but pages are setup
+	  for write combining. This avoids cache management overhead, and can
+	  be faster if pages are mostly untouched by the cpu.  If in doubt,
+	  say Y.
+
 config DMABUF_HEAPS_CMA
 	bool "DMA-BUF CMA Heap"
 	depends on DMABUF_HEAPS && DMA_CMA
diff --git a/drivers/dma-buf/heaps/Makefile b/drivers/dma-buf/heaps/Makefile
index 6e54cdec3da0..085685ec478f 100644
--- a/drivers/dma-buf/heaps/Makefile
+++ b/drivers/dma-buf/heaps/Makefile
@@ -1,4 +1,5 @@
 # SPDX-License-Identifier: GPL-2.0
 obj-y					+= heap-helpers.o
 obj-$(CONFIG_DMABUF_HEAPS_SYSTEM)	+= system_heap.o
+obj-$(CONFIG_DMABUF_HEAPS_SYSTEM_UNCACHED) += system_uncached_heap.o
 obj-$(CONFIG_DMABUF_HEAPS_CMA)		+= cma_heap.o
diff --git a/drivers/dma-buf/heaps/system_uncached_heap.c b/drivers/dma-buf/heaps/system_uncached_heap.c
new file mode 100644
index 000000000000..d23908038376
--- /dev/null
+++ b/drivers/dma-buf/heaps/system_uncached_heap.c
@@ -0,0 +1,392 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Uncached System DMA-Heap exporter
+ *
+ * Copyright (C) 2020 Linaro Ltd.
+ *
+ * Based off of Andrew Davis' SRAM heap:
+ * Copyright (C) 2019 Texas Instruments Incorporated - http://www.ti.com/
+ *	Andrew F. Davis <afd@ti.com>
+ */
+
+#include <linux/dma-mapping.h>
+#include <linux/err.h>
+#include <linux/highmem.h>
+#include <linux/io.h>
+#include <linux/mm.h>
+#include <linux/scatterlist.h>
+#include <linux/slab.h>
+#include <linux/dma-buf.h>
+#include <linux/dma-heap.h>
+
+struct uncached_heap {
+	struct dma_heap *heap;
+};
+
+struct uncached_heap_buffer {
+	struct dma_heap *heap;
+	struct list_head attachments;
+	struct mutex lock;
+	unsigned long len;
+	struct sg_table sg_table;
+	int vmap_cnt;
+	void *vaddr;
+};
+
+struct dma_heap_attachment {
+	struct device *dev;
+	struct sg_table *table;
+	struct list_head list;
+};
+
+static struct sg_table *dup_sg_table(struct sg_table *table)
+{
+	struct sg_table *new_table;
+	int ret, i;
+	struct scatterlist *sg, *new_sg;
+
+	new_table = kzalloc(sizeof(*new_table), GFP_KERNEL);
+	if (!new_table)
+		return ERR_PTR(-ENOMEM);
+
+	ret = sg_alloc_table(new_table, table->nents, GFP_KERNEL);
+	if (ret) {
+		kfree(new_table);
+		return ERR_PTR(-ENOMEM);
+	}
+
+	new_sg = new_table->sgl;
+	for_each_sg(table->sgl, sg, table->nents, i) {
+		memcpy(new_sg, sg, sizeof(*sg));
+		new_sg->dma_address = 0;
+		new_sg = sg_next(new_sg);
+	}
+
+	return new_table;
+}
+
+static int dma_heap_attach(struct dma_buf *dmabuf,
+			   struct dma_buf_attachment *attachment)
+{
+	struct uncached_heap_buffer *buffer = dmabuf->priv;
+	struct dma_heap_attachment *a;
+	struct sg_table *table;
+
+	a = kzalloc(sizeof(*a), GFP_KERNEL);
+	if (!a)
+		return -ENOMEM;
+
+	table = dup_sg_table(&buffer->sg_table);
+	if (IS_ERR(table)) {
+		kfree(a);
+		return -ENOMEM;
+	}
+
+	a->table = table;
+	a->dev = attachment->dev;
+	INIT_LIST_HEAD(&a->list);
+
+	attachment->priv = a;
+
+	mutex_lock(&buffer->lock);
+	list_add(&a->list, &buffer->attachments);
+	mutex_unlock(&buffer->lock);
+
+	return 0;
+}
+
+static void dma_heap_detatch(struct dma_buf *dmabuf,
+			     struct dma_buf_attachment *attachment)
+{
+	struct uncached_heap_buffer *buffer = dmabuf->priv;
+	struct dma_heap_attachment *a = attachment->priv;
+
+	mutex_lock(&buffer->lock);
+	list_del(&a->list);
+	mutex_unlock(&buffer->lock);
+
+	sg_free_table(a->table);
+	kfree(a->table);
+	kfree(a);
+}
+
+static struct sg_table *dma_heap_map_dma_buf(struct dma_buf_attachment *attachment,
+					     enum dma_data_direction direction)
+{
+	struct dma_heap_attachment *a = attachment->priv;
+	struct sg_table *table = a->table;
+
+	if (!dma_map_sg_attrs(attachment->dev, table->sgl, table->nents, direction,
+			      DMA_ATTR_SKIP_CPU_SYNC | DMA_ATTR_WRITE_COMBINE))
+		return ERR_PTR(-ENOMEM);
+
+	return table;
+}
+
+static void dma_heap_unmap_dma_buf(struct dma_buf_attachment *attachment,
+				   struct sg_table *table,
+				   enum dma_data_direction direction)
+{
+	dma_unmap_sg_attrs(attachment->dev, table->sgl, table->nents, direction,
+			   DMA_ATTR_SKIP_CPU_SYNC | DMA_ATTR_WRITE_COMBINE);
+}
+
+static int dma_heap_mmap(struct dma_buf *dmabuf, struct vm_area_struct *vma)
+{
+	struct uncached_heap_buffer *buffer = dmabuf->priv;
+	struct sg_table *table = &buffer->sg_table;
+	unsigned long addr = vma->vm_start;
+	unsigned long offset = vma->vm_pgoff * PAGE_SIZE;
+	struct scatterlist *sg;
+	int i;
+	int ret;
+
+	vma->vm_page_prot = pgprot_writecombine(vma->vm_page_prot);
+
+	for_each_sg(table->sgl, sg, table->nents, i) {
+		struct page *page = sg_page(sg);
+		unsigned long remainder = vma->vm_end - addr;
+		unsigned long len = sg->length;
+
+		if (offset >= sg->length) {
+			offset -= sg->length;
+			continue;
+		} else if (offset) {
+			page += offset / PAGE_SIZE;
+			len = sg->length - offset;
+			offset = 0;
+		}
+		len = min(len, remainder);
+		ret = remap_pfn_range(vma, addr, page_to_pfn(page), len,
+				      vma->vm_page_prot);
+		if (ret)
+			return ret;
+		addr += len;
+		if (addr >= vma->vm_end)
+			return 0;
+	}
+	return 0;
+}
+
+static void *dma_heap_do_vmap(struct uncached_heap_buffer *buffer)
+{
+	struct sg_table *table = &buffer->sg_table;
+	int npages = PAGE_ALIGN(buffer->len) / PAGE_SIZE;
+	struct page **pages = vmalloc(sizeof(struct page *) * npages);
+	struct page **tmp = pages;
+	struct scatterlist *sg;
+	pgprot_t pgprot;
+	void *vaddr;
+	int i, j;
+
+	if (!pages)
+		return ERR_PTR(-ENOMEM);
+
+	pgprot = pgprot_writecombine(PAGE_KERNEL);
+
+	for_each_sg(table->sgl, sg, table->nents, i) {
+		int npages_this_entry = PAGE_ALIGN(sg->length) / PAGE_SIZE;
+		struct page *page = sg_page(sg);
+
+		WARN_ON(i >= npages);
+		for (j = 0; j < npages_this_entry; j++)
+			*(tmp++) = page++;
+	}
+	vaddr = vmap(pages, npages, VM_MAP, pgprot);
+	vfree(pages);
+
+	if (!vaddr)
+		return ERR_PTR(-ENOMEM);
+
+	return vaddr;
+}
+
+static void *dma_heap_buffer_vmap_get(struct uncached_heap_buffer *buffer)
+{
+	void *vaddr;
+
+	if (buffer->vmap_cnt) {
+		buffer->vmap_cnt++;
+		return buffer->vaddr;
+	}
+
+	vaddr = dma_heap_do_vmap(buffer);
+	if (IS_ERR(vaddr))
+		return vaddr;
+
+	buffer->vaddr = vaddr;
+	buffer->vmap_cnt++;
+	return vaddr;
+}
+
+static void dma_heap_buffer_vmap_put(struct uncached_heap_buffer *buffer)
+{
+	if (!--buffer->vmap_cnt) {
+		vunmap(buffer->vaddr);
+		buffer->vaddr = NULL;
+	}
+}
+
+static void *dma_heap_vmap(struct dma_buf *dmabuf)
+{
+	struct uncached_heap_buffer *buffer = dmabuf->priv;
+	void *vaddr;
+
+	mutex_lock(&buffer->lock);
+	vaddr = dma_heap_buffer_vmap_get(buffer);
+	mutex_unlock(&buffer->lock);
+
+	return vaddr;
+}
+
+static void dma_heap_vunmap(struct dma_buf *dmabuf, void *vaddr)
+{
+	struct uncached_heap_buffer *buffer = dmabuf->priv;
+
+	mutex_lock(&buffer->lock);
+	dma_heap_buffer_vmap_put(buffer);
+	mutex_unlock(&buffer->lock);
+}
+
+static void dma_heap_dma_buf_release(struct dma_buf *dmabuf)
+{
+	struct uncached_heap_buffer *buffer = dmabuf->priv;
+	struct sg_table *table;
+	struct scatterlist *sg;
+	int i;
+
+	table = &buffer->sg_table;
+	for_each_sg(table->sgl, sg, table->nents, i)
+		__free_page(sg_page(sg));
+	sg_free_table(table);
+	kfree(buffer);
+}
+
+const struct dma_buf_ops uncached_heap_buf_ops = {
+	.attach = dma_heap_attach,
+	.detach = dma_heap_detatch,
+	.map_dma_buf = dma_heap_map_dma_buf,
+	.unmap_dma_buf = dma_heap_unmap_dma_buf,
+	.mmap = dma_heap_mmap,
+	.vmap = dma_heap_vmap,
+	.vunmap = dma_heap_vunmap,
+	.release = dma_heap_dma_buf_release,
+};
+
+static int uncached_heap_allocate(struct dma_heap *heap,
+				  unsigned long len,
+				  unsigned long fd_flags,
+				  unsigned long heap_flags)
+{
+	struct uncached_heap_buffer *buffer;
+	DEFINE_DMA_BUF_EXPORT_INFO(exp_info);
+	struct dma_buf *dmabuf;
+	struct sg_table *table;
+	struct scatterlist *sg;
+	pgoff_t pagecount;
+	pgoff_t pg;
+	int i, ret = -ENOMEM;
+
+	buffer = kzalloc(sizeof(*buffer), GFP_KERNEL);
+	if (!buffer)
+		return -ENOMEM;
+
+	INIT_LIST_HEAD(&buffer->attachments);
+	mutex_init(&buffer->lock);
+	buffer->heap = heap;
+	buffer->len = len;
+
+	table = &buffer->sg_table;
+	pagecount = len / PAGE_SIZE;
+	if (sg_alloc_table(table, pagecount, GFP_KERNEL))
+		goto free_buffer;
+
+	sg = table->sgl;
+	for (pg = 0; pg < pagecount; pg++) {
+		struct page *page;
+		/*
+		 * Avoid trying to allocate memory if the process
+		 * has been killed by by SIGKILL
+		 */
+		if (fatal_signal_pending(current))
+			goto free_pages;
+		page = alloc_page(GFP_KERNEL | __GFP_ZERO);
+		if (!page)
+			goto free_pages;
+		sg_set_page(sg, page, page_size(page), 0);
+		sg = sg_next(sg);
+	}
+
+	/* create the dmabuf */
+	exp_info.ops = &uncached_heap_buf_ops;
+	exp_info.size = buffer->len;
+	exp_info.flags = fd_flags;
+	exp_info.priv = buffer;
+	dmabuf = dma_buf_export(&exp_info);
+	if (IS_ERR(dmabuf)) {
+		ret = PTR_ERR(dmabuf);
+		goto free_pages;
+	}
+
+	ret = dma_buf_fd(dmabuf, fd_flags);
+	if (ret < 0) {
+		dma_buf_put(dmabuf);
+		/* just return, as put will call release and that will free */
+		return ret;
+	}
+
+	/*
+	 * XXX This is hackish. While the buffer will be uncached, we need
+	 * to initially flush cpu cache, since the the __GFP_ZERO on the
+	 * allocation means the zeroing was done by the cpu and thus it is likely
+	 * cached. Map & flush it out now so we don't get corruption later on.
+	 *
+	 * Ideally we could do this without using the heap device as a dummy dev.
+	 */
+	dma_map_sg_attrs(dma_heap_get_dev(heap), table->sgl, table->nents,
+			 DMA_BIDIRECTIONAL, DMA_ATTR_WRITE_COMBINE);
+	dma_sync_sg_for_device(dma_heap_get_dev(heap), table->sgl, table->nents,
+			       DMA_BIDIRECTIONAL);
+
+	return ret;
+
+free_pages:
+	for_each_sg(table->sgl, sg, table->nents, i)
+		__free_page(sg_page(sg));
+	sg_free_table(table);
+free_buffer:
+	kfree(buffer);
+
+	return ret;
+}
+
+static struct dma_heap_ops uncached_heap_ops = {
+	.allocate = uncached_heap_allocate,
+};
+
+static int uncached_heap_create(void)
+{
+	struct uncached_heap *heap;
+	struct dma_heap_export_info exp_info;
+	static u64 dummy_mask;
+
+	heap = kzalloc(sizeof(*heap), GFP_KERNEL);
+	if (!heap)
+		return -ENOMEM;
+
+	exp_info.name = "system-uncached";
+	exp_info.ops = &uncached_heap_ops;
+	exp_info.priv = heap;
+	heap->heap = dma_heap_add(&exp_info);
+	if (IS_ERR(heap->heap)) {
+		int ret = PTR_ERR(heap->heap);
+
+		kfree(heap);
+		return ret;
+	}
+	dma_heap_get_dev(heap->heap)->dma_mask = &dummy_mask;
+	dma_set_mask(dma_heap_get_dev(heap->heap), DMA_BIT_MASK(64));
+
+	return 0;
+}
+device_initcall(uncached_heap_create);
-- 
2.17.1

Re: [RFC][PATCH 2/2] dma-heap: Add a system-uncached heap

[Robin Murphy]

On 2020-07-29 06:16, John Stultz wrote:
> This adds a heap that allocates non-contiguous buffers that are
> marked as writecombined, so they are not cached by the CPU.
> 
> This is useful, as most graphics buffers are usually not touched
> by the CPU or only written into once by the CPU. So when mapping
> the buffer over and over between devices, we can skip the CPU
> syncing, which saves a lot of cache management overhead, greatly
> improving performance.
> 
> For folk using ION, there was a ION_FLAG_CACHED flag, which
> signaled if the returned buffer should be CPU cacheable or not.
> With DMA-BUF heaps, we have no such flag, and by default the
> current heaps (system and cma) produce CPU cachable buffers.
> So for folks transitioning from ION to DMA-BUF Heaps, this fills
> in some of that missing functionality.
> 
> This does have a few "ugly" bits that were required to get
> the buffer properly flushed out initially which I'd like to
> improve. So feedback would be very welcome!
> 
> Many thanks to Liam Mark for his help to get this working.
> 
> Cc: Sumit Semwal <sumit.semwal@linaro.org>
> Cc: Andrew F. Davis <afd@ti.com>
> Cc: Benjamin Gaignard <benjamin.gaignard@linaro.org>
> Cc: Liam Mark <lmark@codeaurora.org>
> Cc: Laura Abbott <labbott@kernel.org>
> Cc: Brian Starkey <Brian.Starkey@arm.com>
> Cc: Hridya Valsaraju <hridya@google.com>
> Cc: linux-media@vger.kernel.org
> Cc: dri-devel@lists.freedesktop.org
> Signed-off-by: John Stultz <john.stultz@linaro.org>
> ---
>   drivers/dma-buf/heaps/Kconfig                |  10 +
>   drivers/dma-buf/heaps/Makefile               |   1 +
>   drivers/dma-buf/heaps/system_uncached_heap.c | 392 +++++++++++++++++++
>   3 files changed, 403 insertions(+)
>   create mode 100644 drivers/dma-buf/heaps/system_uncached_heap.c
> 
> diff --git a/drivers/dma-buf/heaps/Kconfig b/drivers/dma-buf/heaps/Kconfig
> index a5eef06c4226..420b0ed0a512 100644
> --- a/drivers/dma-buf/heaps/Kconfig
> +++ b/drivers/dma-buf/heaps/Kconfig
> @@ -5,6 +5,16 @@ config DMABUF_HEAPS_SYSTEM
>   	  Choose this option to enable the system dmabuf heap. The system heap
>   	  is backed by pages from the buddy allocator. If in doubt, say Y.
>   
> +config DMABUF_HEAPS_SYSTEM_UNCACHED
> +	bool "DMA-BUF Uncached System Heap"
> +	depends on DMABUF_HEAPS
> +	help
> +	  Choose this option to enable the uncached system dmabuf heap. This
> +	  heap is backed by pages from the buddy allocator, but pages are setup
> +	  for write combining. This avoids cache management overhead, and can
> +	  be faster if pages are mostly untouched by the cpu.  If in doubt,
> +	  say Y.
> +
>   config DMABUF_HEAPS_CMA
>   	bool "DMA-BUF CMA Heap"
>   	depends on DMABUF_HEAPS && DMA_CMA
> diff --git a/drivers/dma-buf/heaps/Makefile b/drivers/dma-buf/heaps/Makefile
> index 6e54cdec3da0..085685ec478f 100644
> --- a/drivers/dma-buf/heaps/Makefile
> +++ b/drivers/dma-buf/heaps/Makefile
> @@ -1,4 +1,5 @@
>   # SPDX-License-Identifier: GPL-2.0
>   obj-y					+= heap-helpers.o
>   obj-$(CONFIG_DMABUF_HEAPS_SYSTEM)	+= system_heap.o
> +obj-$(CONFIG_DMABUF_HEAPS_SYSTEM_UNCACHED) += system_uncached_heap.o
>   obj-$(CONFIG_DMABUF_HEAPS_CMA)		+= cma_heap.o
> diff --git a/drivers/dma-buf/heaps/system_uncached_heap.c b/drivers/dma-buf/heaps/system_uncached_heap.c
> new file mode 100644
> index 000000000000..d23908038376
> --- /dev/null
> +++ b/drivers/dma-buf/heaps/system_uncached_heap.c
> @@ -0,0 +1,392 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Uncached System DMA-Heap exporter
> + *
> + * Copyright (C) 2020 Linaro Ltd.
> + *
> + * Based off of Andrew Davis' SRAM heap:
> + * Copyright (C) 2019 Texas Instruments Incorporated - http://www.ti.com/
> + *	Andrew F. Davis <afd@ti.com>
> + */
> +
> +#include <linux/dma-mapping.h>
> +#include <linux/err.h>
> +#include <linux/highmem.h>
> +#include <linux/io.h>
> +#include <linux/mm.h>
> +#include <linux/scatterlist.h>
> +#include <linux/slab.h>
> +#include <linux/dma-buf.h>
> +#include <linux/dma-heap.h>
> +
> +struct uncached_heap {
> +	struct dma_heap *heap;
> +};
> +
> +struct uncached_heap_buffer {
> +	struct dma_heap *heap;
> +	struct list_head attachments;
> +	struct mutex lock;
> +	unsigned long len;
> +	struct sg_table sg_table;
> +	int vmap_cnt;
> +	void *vaddr;
> +};
> +
> +struct dma_heap_attachment {
> +	struct device *dev;
> +	struct sg_table *table;
> +	struct list_head list;
> +};
> +
> +static struct sg_table *dup_sg_table(struct sg_table *table)
> +{
> +	struct sg_table *new_table;
> +	int ret, i;
> +	struct scatterlist *sg, *new_sg;
> +
> +	new_table = kzalloc(sizeof(*new_table), GFP_KERNEL);
> +	if (!new_table)
> +		return ERR_PTR(-ENOMEM);
> +
> +	ret = sg_alloc_table(new_table, table->nents, GFP_KERNEL);
> +	if (ret) {
> +		kfree(new_table);
> +		return ERR_PTR(-ENOMEM);
> +	}
> +
> +	new_sg = new_table->sgl;
> +	for_each_sg(table->sgl, sg, table->nents, i) {

Consider using the new sgtable helpers that are just about to land - in 
this case, for_each_sgtable_sg().

> +		memcpy(new_sg, sg, sizeof(*sg));
> +		new_sg->dma_address = 0;

This seems a little bit hairy, as in theory a consumer could still treat 
a nonzero DMA length as the address being valid. Rather than copying the 
whole entry then trying to undo parts of that, maybe just:

	sg_set_page(new_sg, sg_page(sg), sg->len, sg->offset);

?

> +		new_sg = sg_next(new_sg);
> +	}
> +
> +	return new_table;
> +}
> +
> +static int dma_heap_attach(struct dma_buf *dmabuf,
> +			   struct dma_buf_attachment *attachment)
> +{
> +	struct uncached_heap_buffer *buffer = dmabuf->priv;
> +	struct dma_heap_attachment *a;
> +	struct sg_table *table;
> +
> +	a = kzalloc(sizeof(*a), GFP_KERNEL);
> +	if (!a)
> +		return -ENOMEM;
> +
> +	table = dup_sg_table(&buffer->sg_table);
> +	if (IS_ERR(table)) {
> +		kfree(a);
> +		return -ENOMEM;
> +	}
> +
> +	a->table = table;
> +	a->dev = attachment->dev;
> +	INIT_LIST_HEAD(&a->list);
> +
> +	attachment->priv = a;
> +
> +	mutex_lock(&buffer->lock);
> +	list_add(&a->list, &buffer->attachments);
> +	mutex_unlock(&buffer->lock);
> +
> +	return 0;
> +}
> +
> +static void dma_heap_detatch(struct dma_buf *dmabuf,
> +			     struct dma_buf_attachment *attachment)
> +{
> +	struct uncached_heap_buffer *buffer = dmabuf->priv;
> +	struct dma_heap_attachment *a = attachment->priv;
> +
> +	mutex_lock(&buffer->lock);
> +	list_del(&a->list);
> +	mutex_unlock(&buffer->lock);
> +
> +	sg_free_table(a->table);
> +	kfree(a->table);
> +	kfree(a);
> +}
> +
> +static struct sg_table *dma_heap_map_dma_buf(struct dma_buf_attachment *attachment,
> +					     enum dma_data_direction direction)
> +{
> +	struct dma_heap_attachment *a = attachment->priv;
> +	struct sg_table *table = a->table;
> +
> +	if (!dma_map_sg_attrs(attachment->dev, table->sgl, table->nents, direction,
> +			      DMA_ATTR_SKIP_CPU_SYNC | DMA_ATTR_WRITE_COMBINE))

dma_map_sgtable()

Also, DMA_ATTR_WRITE_COMBINE is meaningless for streaming DMA.

> +		return ERR_PTR(-ENOMEM);
> +
> +	return table;
> +}
> +
> +static void dma_heap_unmap_dma_buf(struct dma_buf_attachment *attachment,
> +				   struct sg_table *table,
> +				   enum dma_data_direction direction)
> +{
> +	dma_unmap_sg_attrs(attachment->dev, table->sgl, table->nents, direction,
> +			   DMA_ATTR_SKIP_CPU_SYNC | DMA_ATTR_WRITE_COMBINE);

Similarly.

> +}
> +
> +static int dma_heap_mmap(struct dma_buf *dmabuf, struct vm_area_struct *vma)
> +{
> +	struct uncached_heap_buffer *buffer = dmabuf->priv;
> +	struct sg_table *table = &buffer->sg_table;
> +	unsigned long addr = vma->vm_start;
> +	unsigned long offset = vma->vm_pgoff * PAGE_SIZE;
> +	struct scatterlist *sg;
> +	int i;
> +	int ret;
> +
> +	vma->vm_page_prot = pgprot_writecombine(vma->vm_page_prot);
> +
> +	for_each_sg(table->sgl, sg, table->nents, i) {
> +		struct page *page = sg_page(sg);
> +		unsigned long remainder = vma->vm_end - addr;
> +		unsigned long len = sg->length;
> +
> +		if (offset >= sg->length) {
> +			offset -= sg->length;
> +			continue;
> +		} else if (offset) {
> +			page += offset / PAGE_SIZE;
> +			len = sg->length - offset;
> +			offset = 0;
> +		}
> +		len = min(len, remainder);
> +		ret = remap_pfn_range(vma, addr, page_to_pfn(page), len,
> +				      vma->vm_page_prot);
> +		if (ret)
> +			return ret;
> +		addr += len;
> +		if (addr >= vma->vm_end)
> +			return 0;
> +	}
> +	return 0;
> +}
> +
> +static void *dma_heap_do_vmap(struct uncached_heap_buffer *buffer)
> +{
> +	struct sg_table *table = &buffer->sg_table;
> +	int npages = PAGE_ALIGN(buffer->len) / PAGE_SIZE;
> +	struct page **pages = vmalloc(sizeof(struct page *) * npages);
> +	struct page **tmp = pages;
> +	struct scatterlist *sg;
> +	pgprot_t pgprot;
> +	void *vaddr;
> +	int i, j;
> +
> +	if (!pages)
> +		return ERR_PTR(-ENOMEM);
> +
> +	pgprot = pgprot_writecombine(PAGE_KERNEL);
> +
> +	for_each_sg(table->sgl, sg, table->nents, i) {

for_each_sg_page()

> +		int npages_this_entry = PAGE_ALIGN(sg->length) / PAGE_SIZE;
> +		struct page *page = sg_page(sg);
> +
> +		WARN_ON(i >= npages);
> +		for (j = 0; j < npages_this_entry; j++)
> +			*(tmp++) = page++;
> +	}
> +	vaddr = vmap(pages, npages, VM_MAP, pgprot);
> +	vfree(pages);
> +
> +	if (!vaddr)
> +		return ERR_PTR(-ENOMEM);
> +
> +	return vaddr;
> +}
> +
> +static void *dma_heap_buffer_vmap_get(struct uncached_heap_buffer *buffer)
> +{
> +	void *vaddr;
> +
> +	if (buffer->vmap_cnt) {
> +		buffer->vmap_cnt++;
> +		return buffer->vaddr;
> +	}
> +
> +	vaddr = dma_heap_do_vmap(buffer);
> +	if (IS_ERR(vaddr))
> +		return vaddr;
> +
> +	buffer->vaddr = vaddr;
> +	buffer->vmap_cnt++;
> +	return vaddr;
> +}
> +
> +static void dma_heap_buffer_vmap_put(struct uncached_heap_buffer *buffer)
> +{
> +	if (!--buffer->vmap_cnt) {
> +		vunmap(buffer->vaddr);
> +		buffer->vaddr = NULL;
> +	}
> +}
> +
> +static void *dma_heap_vmap(struct dma_buf *dmabuf)
> +{
> +	struct uncached_heap_buffer *buffer = dmabuf->priv;
> +	void *vaddr;
> +
> +	mutex_lock(&buffer->lock);
> +	vaddr = dma_heap_buffer_vmap_get(buffer);
> +	mutex_unlock(&buffer->lock);
> +
> +	return vaddr;
> +}
> +
> +static void dma_heap_vunmap(struct dma_buf *dmabuf, void *vaddr)
> +{
> +	struct uncached_heap_buffer *buffer = dmabuf->priv;
> +
> +	mutex_lock(&buffer->lock);
> +	dma_heap_buffer_vmap_put(buffer);
> +	mutex_unlock(&buffer->lock);
> +}
> +
> +static void dma_heap_dma_buf_release(struct dma_buf *dmabuf)
> +{
> +	struct uncached_heap_buffer *buffer = dmabuf->priv;
> +	struct sg_table *table;
> +	struct scatterlist *sg;
> +	int i;
> +
> +	table = &buffer->sg_table;
> +	for_each_sg(table->sgl, sg, table->nents, i)
> +		__free_page(sg_page(sg));
> +	sg_free_table(table);
> +	kfree(buffer);
> +}
> +
> +const struct dma_buf_ops uncached_heap_buf_ops = {
> +	.attach = dma_heap_attach,
> +	.detach = dma_heap_detatch,
> +	.map_dma_buf = dma_heap_map_dma_buf,
> +	.unmap_dma_buf = dma_heap_unmap_dma_buf,
> +	.mmap = dma_heap_mmap,
> +	.vmap = dma_heap_vmap,
> +	.vunmap = dma_heap_vunmap,
> +	.release = dma_heap_dma_buf_release,
> +};
> +
> +static int uncached_heap_allocate(struct dma_heap *heap,
> +				  unsigned long len,
> +				  unsigned long fd_flags,
> +				  unsigned long heap_flags)
> +{
> +	struct uncached_heap_buffer *buffer;
> +	DEFINE_DMA_BUF_EXPORT_INFO(exp_info);
> +	struct dma_buf *dmabuf;
> +	struct sg_table *table;
> +	struct scatterlist *sg;
> +	pgoff_t pagecount;
> +	pgoff_t pg;
> +	int i, ret = -ENOMEM;
> +
> +	buffer = kzalloc(sizeof(*buffer), GFP_KERNEL);
> +	if (!buffer)
> +		return -ENOMEM;
> +
> +	INIT_LIST_HEAD(&buffer->attachments);
> +	mutex_init(&buffer->lock);
> +	buffer->heap = heap;
> +	buffer->len = len;
> +
> +	table = &buffer->sg_table;
> +	pagecount = len / PAGE_SIZE;
> +	if (sg_alloc_table(table, pagecount, GFP_KERNEL))
> +		goto free_buffer;
> +
> +	sg = table->sgl;
> +	for (pg = 0; pg < pagecount; pg++) {
> +		struct page *page;
> +		/*
> +		 * Avoid trying to allocate memory if the process
> +		 * has been killed by by SIGKILL
> +		 */
> +		if (fatal_signal_pending(current))
> +			goto free_pages;
> +		page = alloc_page(GFP_KERNEL | __GFP_ZERO);
> +		if (!page)
> +			goto free_pages;
> +		sg_set_page(sg, page, page_size(page), 0);
> +		sg = sg_next(sg);
> +	}
> +
> +	/* create the dmabuf */
> +	exp_info.ops = &uncached_heap_buf_ops;
> +	exp_info.size = buffer->len;
> +	exp_info.flags = fd_flags;
> +	exp_info.priv = buffer;
> +	dmabuf = dma_buf_export(&exp_info);
> +	if (IS_ERR(dmabuf)) {
> +		ret = PTR_ERR(dmabuf);
> +		goto free_pages;
> +	}
> +
> +	ret = dma_buf_fd(dmabuf, fd_flags);
> +	if (ret < 0) {
> +		dma_buf_put(dmabuf);
> +		/* just return, as put will call release and that will free */
> +		return ret;
> +	}
> +
> +	/*
> +	 * XXX This is hackish. While the buffer will be uncached, we need
> +	 * to initially flush cpu cache, since the the __GFP_ZERO on the
> +	 * allocation means the zeroing was done by the cpu and thus it is likely
> +	 * cached. Map & flush it out now so we don't get corruption later on.
> +	 *
> +	 * Ideally we could do this without using the heap device as a dummy dev.
> +	 */
> +	dma_map_sg_attrs(dma_heap_get_dev(heap), table->sgl, table->nents,
> +			 DMA_BIDIRECTIONAL, DMA_ATTR_WRITE_COMBINE);

Again, DMA_ATTR_WRITE_COMBINE is meaningless here.

> +	dma_sync_sg_for_device(dma_heap_get_dev(heap), table->sgl, table->nents,
> +			       DMA_BIDIRECTIONAL);

This doesn't do anything that the map hasn't already just done.

> +
> +	return ret;
> +
> +free_pages:
> +	for_each_sg(table->sgl, sg, table->nents, i)
> +		__free_page(sg_page(sg));
> +	sg_free_table(table);
> +free_buffer:
> +	kfree(buffer);
> +
> +	return ret;
> +}
> +
> +static struct dma_heap_ops uncached_heap_ops = {
> +	.allocate = uncached_heap_allocate,
> +};
> +
> +static int uncached_heap_create(void)
> +{
> +	struct uncached_heap *heap;
> +	struct dma_heap_export_info exp_info;
> +	static u64 dummy_mask;
> +
> +	heap = kzalloc(sizeof(*heap), GFP_KERNEL);
> +	if (!heap)
> +		return -ENOMEM;
> +
> +	exp_info.name = "system-uncached";
> +	exp_info.ops = &uncached_heap_ops;
> +	exp_info.priv = heap;
> +	heap->heap = dma_heap_add(&exp_info);
> +	if (IS_ERR(heap->heap)) {
> +		int ret = PTR_ERR(heap->heap);
> +
> +		kfree(heap);
> +		return ret;
> +	}
> +	dma_heap_get_dev(heap->heap)->dma_mask = &dummy_mask;
> +	dma_set_mask(dma_heap_get_dev(heap->heap), DMA_BIT_MASK(64));

Much as I'd hate to encourage using dma_coerce_mask_and_coherent(), I'm 
not sure this is really any better :/

Robin.

> +
> +	return 0;
> +}
> +device_initcall(uncached_heap_create);
> 

Re: [RFC][PATCH 2/2] dma-heap: Add a system-uncached heap

[John Stultz]

On Mon, Aug 3, 2020 at 4:06 AM Robin Murphy <robin.murphy@arm.com> wrote:
>
> On 2020-07-29 06:16, John Stultz wrote:
> > This adds a heap that allocates non-contiguous buffers that are
> > marked as writecombined, so they are not cached by the CPU.
> >
...
> > +     ret = sg_alloc_table(new_table, table->nents, GFP_KERNEL);
> > +     if (ret) {
> > +             kfree(new_table);
> > +             return ERR_PTR(-ENOMEM);
> > +     }
> > +
> > +     new_sg = new_table->sgl;
> > +     for_each_sg(table->sgl, sg, table->nents, i) {
>
> Consider using the new sgtable helpers that are just about to land - in
> this case, for_each_sgtable_sg().

Ack! Thanks for the suggestion!


> > +             memcpy(new_sg, sg, sizeof(*sg));
> > +             new_sg->dma_address = 0;
>
> This seems a little bit hairy, as in theory a consumer could still treat
> a nonzero DMA length as the address being valid. Rather than copying the
> whole entry then trying to undo parts of that, maybe just:
>
>         sg_set_page(new_sg, sg_page(sg), sg->len, sg->offset);
>
> ?

Sounds good.


> > +static struct sg_table *dma_heap_map_dma_buf(struct dma_buf_attachment *attachment,
> > +                                          enum dma_data_direction direction)
> > +{
> > +     struct dma_heap_attachment *a = attachment->priv;
> > +     struct sg_table *table = a->table;
> > +
> > +     if (!dma_map_sg_attrs(attachment->dev, table->sgl, table->nents, direction,
> > +                           DMA_ATTR_SKIP_CPU_SYNC | DMA_ATTR_WRITE_COMBINE))
>
> dma_map_sgtable()
>
> Also, DMA_ATTR_WRITE_COMBINE is meaningless for streaming DMA.
>

Hrm. Ok, my grasp of "streaming" vs "consistent" definitions are maybe
slightly off, since while we are mapping and unmapping buffers, the
point of this heap is that the allocated memory is uncached/coherent,
so we avoid the cache sync overhead on each mapping/unmapping, which I
thought was closer to the "consistent" definition.

But maybe if the mapping and unmapping part is really the key
difference, then ok.

Either way, from my testing, you seem to be right that the
ATTR_WRITE_COMBINE doesn't seem to make any difference in behavior.

> > +     pgprot = pgprot_writecombine(PAGE_KERNEL);
> > +
> > +     for_each_sg(table->sgl, sg, table->nents, i) {
>
> for_each_sg_page()

Ack.

> > +     /*
> > +      * XXX This is hackish. While the buffer will be uncached, we need
> > +      * to initially flush cpu cache, since the the __GFP_ZERO on the
> > +      * allocation means the zeroing was done by the cpu and thus it is likely
> > +      * cached. Map & flush it out now so we don't get corruption later on.
> > +      *
> > +      * Ideally we could do this without using the heap device as a dummy dev.
> > +      */
> > +     dma_map_sg_attrs(dma_heap_get_dev(heap), table->sgl, table->nents,
> > +                      DMA_BIDIRECTIONAL, DMA_ATTR_WRITE_COMBINE);
>
> Again, DMA_ATTR_WRITE_COMBINE is meaningless here.
>
> > +     dma_sync_sg_for_device(dma_heap_get_dev(heap), table->sgl, table->nents,
> > +                            DMA_BIDIRECTIONAL);
>
> This doesn't do anything that the map hasn't already just done.

Good point!

> > +     }
> > +     dma_heap_get_dev(heap->heap)->dma_mask = &dummy_mask;
> > +     dma_set_mask(dma_heap_get_dev(heap->heap), DMA_BIT_MASK(64));
>
> Much as I'd hate to encourage using dma_coerce_mask_and_coherent(), I'm
> not sure this is really any better :/

Sounds fair.

Thanks so much for the review, I really appreciate the feedback!
(Sorry I was a little slow to respond. The merge window has really
been something this cycle.. :P)

I'll get this all integrated and resend the patch here shortly.

thanks
-john