[v3] misc: sram: Add DMA-BUF Heap exporting of SRAM areas

Commit Message

Andrew Davis July 13, 2023, 7:13 p.m. UTC

This new export type exposes to userspace the SRAM area as a DMA-BUF Heap,
this allows for allocations of DMA-BUFs that can be consumed by various
DMA-BUF supporting devices.

Signed-off-by: Andrew Davis <[e-mail]>
---

Changes from v2:
 - Make sram_dma_heap_allocate static (kernel test robot)
 - Rebase on v6.5-rc1

 drivers/misc/Kconfig         |   7 +
 drivers/misc/Makefile        |   1 +
 drivers/misc/sram-dma-heap.c | 245 +++++++++++++++++++++++++++++++++++
 drivers/misc/sram.c          |   6 +
 drivers/misc/sram.h          |  16 +++
 5 files changed, 275 insertions(+)
 create mode 100644 drivers/misc/sram-dma-heap.c

Comments

Greg KH July 13, 2023, 7:27 p.m. UTC | #1

On Thu, Jul 13, 2023 at 02:13:16PM -0500, Andrew Davis wrote:
> +int sram_add_dma_heap(struct sram_dev *sram,
> +		      struct sram_reserve *block,
> +		      phys_addr_t start,
> +		      struct sram_partition *part)
> +{
> +	struct sram_dma_heap *sram_dma_heap;
> +	struct dma_heap_export_info exp_info;
> +
> +	dev_info(sram->dev, "Exporting SRAM Heap '%s'\n", block->label);

When drivers are working properly, they are quiet.

thanks,

greg k-h

Greg KH July 13, 2023, 7:28 p.m. UTC | #2

On Thu, Jul 13, 2023 at 02:13:16PM -0500, Andrew Davis wrote:
> This new export type exposes to userspace the SRAM area as a DMA-BUF Heap,
> this allows for allocations of DMA-BUFs that can be consumed by various
> DMA-BUF supporting devices.

What devices exactly?

And what userspace tools/programs are going to use this api?

> 
> Signed-off-by: Andrew Davis <[e-mail]>
> ---
> 
> Changes from v2:
>  - Make sram_dma_heap_allocate static (kernel test robot)
>  - Rebase on v6.5-rc1
> 
>  drivers/misc/Kconfig         |   7 +
>  drivers/misc/Makefile        |   1 +
>  drivers/misc/sram-dma-heap.c | 245 +++++++++++++++++++++++++++++++++++
>  drivers/misc/sram.c          |   6 +
>  drivers/misc/sram.h          |  16 +++
>  5 files changed, 275 insertions(+)
>  create mode 100644 drivers/misc/sram-dma-heap.c
> 
> diff --git a/drivers/misc/Kconfig b/drivers/misc/Kconfig
> index 75e427f124b28..ee34dfb61605f 100644
> --- a/drivers/misc/Kconfig
> +++ b/drivers/misc/Kconfig
> @@ -448,6 +448,13 @@ config SRAM
>  config SRAM_EXEC
>  	bool
>  
> +config SRAM_DMA_HEAP
> +	bool "Export on-chip SRAM pools using DMA-Heaps"
> +	depends on DMABUF_HEAPS && SRAM
> +	help
> +	  This driver allows the export of on-chip SRAM marked as both pool
> +	  and exportable to userspace using the DMA-Heaps interface.

Module name?

>  config DW_XDATA_PCIE
>  	depends on PCI
>  	tristate "Synopsys DesignWare xData PCIe driver"
> diff --git a/drivers/misc/Makefile b/drivers/misc/Makefile
> index f2a4d1ff65d46..5e7516bfaa8de 100644
> --- a/drivers/misc/Makefile
> +++ b/drivers/misc/Makefile
> @@ -47,6 +47,7 @@ obj-$(CONFIG_VMWARE_VMCI)	+= vmw_vmci/
>  obj-$(CONFIG_LATTICE_ECP3_CONFIG)	+= lattice-ecp3-config.o
>  obj-$(CONFIG_SRAM)		+= sram.o
>  obj-$(CONFIG_SRAM_EXEC)		+= sram-exec.o
> +obj-$(CONFIG_SRAM_DMA_HEAP)	+= sram-dma-heap.o
>  obj-$(CONFIG_GENWQE)		+= genwqe/
>  obj-$(CONFIG_ECHO)		+= echo/
>  obj-$(CONFIG_CXL_BASE)		+= cxl/
> diff --git a/drivers/misc/sram-dma-heap.c b/drivers/misc/sram-dma-heap.c
> new file mode 100644
> index 0000000000000..c054c04dff33e
> --- /dev/null
> +++ b/drivers/misc/sram-dma-heap.c
> @@ -0,0 +1,245 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * SRAM DMA-Heap userspace exporter
> + *
> + * Copyright (C) 2019-2022 Texas Instruments Incorporated - https://www.ti.com/
> + *	Andrew Davis <[e-mail]>

It's 2023 :(

And this needs review from the dma-buf maintainers before I could do
anything with it.

thanks,

greg k-h

Christian König July 14, 2023, 7:45 a.m. UTC | #3

Am 13.07.23 um 21:28 schrieb Greg Kroah-Hartman:
> On Thu, Jul 13, 2023 at 02:13:16PM -0500, Andrew Davis wrote:
>> This new export type exposes to userspace the SRAM area as a DMA-BUF Heap,
>> this allows for allocations of DMA-BUFs that can be consumed by various
>> DMA-BUF supporting devices.
> What devices exactly?
>
> And what userspace tools/programs are going to use this api?
>
>> Signed-off-by: Andrew Davis <[e-mail]>
>> ---
>>
>> Changes from v2:
>>   - Make sram_dma_heap_allocate static (kernel test robot)
>>   - Rebase on v6.5-rc1
>>
>>   drivers/misc/Kconfig         |   7 +
>>   drivers/misc/Makefile        |   1 +
>>   drivers/misc/sram-dma-heap.c | 245 +++++++++++++++++++++++++++++++++++
>>   drivers/misc/sram.c          |   6 +
>>   drivers/misc/sram.h          |  16 +++
>>   5 files changed, 275 insertions(+)
>>   create mode 100644 drivers/misc/sram-dma-heap.c
>>
>> diff --git a/drivers/misc/Kconfig b/drivers/misc/Kconfig
>> index 75e427f124b28..ee34dfb61605f 100644
>> --- a/drivers/misc/Kconfig
>> +++ b/drivers/misc/Kconfig
>> @@ -448,6 +448,13 @@ config SRAM
>>   config SRAM_EXEC
>>   	bool
>>   
>> +config SRAM_DMA_HEAP
>> +	bool "Export on-chip SRAM pools using DMA-Heaps"
>> +	depends on DMABUF_HEAPS && SRAM
>> +	help
>> +	  This driver allows the export of on-chip SRAM marked as both pool
>> +	  and exportable to userspace using the DMA-Heaps interface.
> Module name?
>
>>   config DW_XDATA_PCIE
>>   	depends on PCI
>>   	tristate "Synopsys DesignWare xData PCIe driver"
>> diff --git a/drivers/misc/Makefile b/drivers/misc/Makefile
>> index f2a4d1ff65d46..5e7516bfaa8de 100644
>> --- a/drivers/misc/Makefile
>> +++ b/drivers/misc/Makefile
>> @@ -47,6 +47,7 @@ obj-$(CONFIG_VMWARE_VMCI)	+= vmw_vmci/
>>   obj-$(CONFIG_LATTICE_ECP3_CONFIG)	+= lattice-ecp3-config.o
>>   obj-$(CONFIG_SRAM)		+= sram.o
>>   obj-$(CONFIG_SRAM_EXEC)		+= sram-exec.o
>> +obj-$(CONFIG_SRAM_DMA_HEAP)	+= sram-dma-heap.o
>>   obj-$(CONFIG_GENWQE)		+= genwqe/
>>   obj-$(CONFIG_ECHO)		+= echo/
>>   obj-$(CONFIG_CXL_BASE)		+= cxl/
>> diff --git a/drivers/misc/sram-dma-heap.c b/drivers/misc/sram-dma-heap.c
>> new file mode 100644
>> index 0000000000000..c054c04dff33e
>> --- /dev/null
>> +++ b/drivers/misc/sram-dma-heap.c
>> @@ -0,0 +1,245 @@
>> +// SPDX-License-Identifier: GPL-2.0
>> +/*
>> + * SRAM DMA-Heap userspace exporter
>> + *
>> + * Copyright (C) 2019-2022 Texas Instruments Incorporated - https://www.ti.com/
>> + *	Andrew Davis <[e-mail]>
> It's 2023 :(
>
> And this needs review from the dma-buf maintainers before I could do
> anything with it.

Yeah, agree. Thanks Greg.

It would be nice if you explicitly CC the maintainers for DMA-buf and 
DMA-buf heaps as well.

Of hand I can only find the version from 2020 in the LKML archives.

Regards,
Christian.

>
> thanks,
>
> greg k-h
> _______________________________________________
> Linaro-mm-sig mailing list -- [e-mail]
> To unsubscribe send an email to [e-mail]

Andrew Davis Aug. 2, 2023, 4:33 p.m. UTC | #4

On 7/13/23 2:27 PM, Greg Kroah-Hartman wrote:
> On Thu, Jul 13, 2023 at 02:13:16PM -0500, Andrew Davis wrote:
>> +int sram_add_dma_heap(struct sram_dev *sram,
>> +		      struct sram_reserve *block,
>> +		      phys_addr_t start,
>> +		      struct sram_partition *part)
>> +{
>> +	struct sram_dma_heap *sram_dma_heap;
>> +	struct dma_heap_export_info exp_info;
>> +
>> +	dev_info(sram->dev, "Exporting SRAM Heap '%s'\n", block->label);
> 
> When drivers are working properly, they are quiet.
> 

This should only be printed once in early boot when the memory is added,
I was wanting this to match the other memory exporters/output at the
beginning of boot logs.

But quiet is fine too, will change this to dev_dbg() for v4.

Thanks,
Andrew

> thanks,
> 
> greg k-h

Robin Murphy Aug. 17, 2023, 1:13 p.m. UTC | #5

On 2023-07-13 20:13, Andrew Davis wrote:
> This new export type exposes to userspace the SRAM area as a DMA-BUF Heap,
> this allows for allocations of DMA-BUFs that can be consumed by various
> DMA-BUF supporting devices.
> 
> Signed-off-by: Andrew Davis <[e-mail]>
> ---
> 
> Changes from v2:
>   - Make sram_dma_heap_allocate static (kernel test robot)
>   - Rebase on v6.5-rc1
> 
>   drivers/misc/Kconfig         |   7 +
>   drivers/misc/Makefile        |   1 +
>   drivers/misc/sram-dma-heap.c | 245 +++++++++++++++++++++++++++++++++++
>   drivers/misc/sram.c          |   6 +
>   drivers/misc/sram.h          |  16 +++
>   5 files changed, 275 insertions(+)
>   create mode 100644 drivers/misc/sram-dma-heap.c
> 
> diff --git a/drivers/misc/Kconfig b/drivers/misc/Kconfig
> index 75e427f124b28..ee34dfb61605f 100644
> --- a/drivers/misc/Kconfig
> +++ b/drivers/misc/Kconfig
> @@ -448,6 +448,13 @@ config SRAM
>   config SRAM_EXEC
>   	bool
>   
> +config SRAM_DMA_HEAP
> +	bool "Export on-chip SRAM pools using DMA-Heaps"
> +	depends on DMABUF_HEAPS && SRAM
> +	help
> +	  This driver allows the export of on-chip SRAM marked as both pool
> +	  and exportable to userspace using the DMA-Heaps interface.
> +
>   config DW_XDATA_PCIE
>   	depends on PCI
>   	tristate "Synopsys DesignWare xData PCIe driver"
> diff --git a/drivers/misc/Makefile b/drivers/misc/Makefile
> index f2a4d1ff65d46..5e7516bfaa8de 100644
> --- a/drivers/misc/Makefile
> +++ b/drivers/misc/Makefile
> @@ -47,6 +47,7 @@ obj-$(CONFIG_VMWARE_VMCI)	+= vmw_vmci/
>   obj-$(CONFIG_LATTICE_ECP3_CONFIG)	+= lattice-ecp3-config.o
>   obj-$(CONFIG_SRAM)		+= sram.o
>   obj-$(CONFIG_SRAM_EXEC)		+= sram-exec.o
> +obj-$(CONFIG_SRAM_DMA_HEAP)	+= sram-dma-heap.o
>   obj-$(CONFIG_GENWQE)		+= genwqe/
>   obj-$(CONFIG_ECHO)		+= echo/
>   obj-$(CONFIG_CXL_BASE)		+= cxl/
> diff --git a/drivers/misc/sram-dma-heap.c b/drivers/misc/sram-dma-heap.c
> new file mode 100644
> index 0000000000000..c054c04dff33e
> --- /dev/null
> +++ b/drivers/misc/sram-dma-heap.c
> @@ -0,0 +1,245 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * SRAM DMA-Heap userspace exporter
> + *
> + * Copyright (C) 2019-2022 Texas Instruments Incorporated - https://www.ti.com/
> + *	Andrew Davis <[e-mail]>
> + */
> +
> +#include <linux/dma-mapping.h>
> +#include <linux/err.h>
> +#include <linux/genalloc.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>
> +
> +#include "sram.h"
> +
> +struct sram_dma_heap {
> +	struct dma_heap *heap;
> +	struct gen_pool *pool;
> +};
> +
> +struct sram_dma_heap_buffer {
> +	struct gen_pool *pool;
> +	struct list_head attachments;
> +	struct mutex attachments_lock;
> +	unsigned long len;
> +	void *vaddr;
> +	phys_addr_t paddr;
> +};
> +
> +struct dma_heap_attachment {
> +	struct device *dev;
> +	struct sg_table *table;
> +	struct list_head list;
> +};
> +
> +static int dma_heap_attach(struct dma_buf *dmabuf,
> +			   struct dma_buf_attachment *attachment)
> +{
> +	struct sram_dma_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 = kmalloc(sizeof(*table), GFP_KERNEL);
> +	if (!table) {
> +		kfree(a);
> +		return -ENOMEM;
> +	}
> +	if (sg_alloc_table(table, 1, GFP_KERNEL)) {
> +		kfree(table);
> +		kfree(a);
> +		return -ENOMEM;
> +	}
> +	sg_set_page(table->sgl, pfn_to_page(PFN_DOWN(buffer->paddr)), buffer->len, 0);

What happens if someone (reasonably) assumes that this struct page 
pointer isn't completely made up, and dereferences it?

(That's if pfn_to_page() itself doesn't blow up, which it potentially 
might, at least under CONFIG_SPARSEMEM)

I think this needs to be treated as P2PDMA if it's going to have any 
hope of working robustly.

> +
> +	a->table = table;
> +	a->dev = attachment->dev;
> +	INIT_LIST_HEAD(&a->list);
> +
> +	attachment->priv = a;
> +
> +	mutex_lock(&buffer->attachments_lock);
> +	list_add(&a->list, &buffer->attachments);
> +	mutex_unlock(&buffer->attachments_lock);
> +
> +	return 0;
> +}
> +
> +static void dma_heap_detatch(struct dma_buf *dmabuf,
> +			     struct dma_buf_attachment *attachment)
> +{
> +	struct sram_dma_heap_buffer *buffer = dmabuf->priv;
> +	struct dma_heap_attachment *a = attachment->priv;
> +
> +	mutex_lock(&buffer->attachments_lock);
> +	list_del(&a->list);
> +	mutex_unlock(&buffer->attachments_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;
> +
> +	/*
> +	 * As this heap is backed by uncached SRAM memory we do not need to
> +	 * perform any sync operations on the buffer before allowing device
> +	 * domain access. For this reason we use SKIP_CPU_SYNC and also do
> +	 * not use or provide begin/end_cpu_access() dma-buf functions.
> +	 */

I bet that works really well with SWIOTLB ;)

Also note that SKIP_CPU_SYNC is only a hint, so the DMA API 
implementation is still at liberty to do the fatally dangerous things 
you're hoping it won't (e.g. dereferencing sg_virt()...)

Thanks,
Robin.

> +	if (!dma_map_sg_attrs(attachment->dev, table->sgl, table->nents,
> +			      direction, DMA_ATTR_SKIP_CPU_SYNC))
> +		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);
> +}
> +
> +static void dma_heap_dma_buf_release(struct dma_buf *dmabuf)
> +{
> +	struct sram_dma_heap_buffer *buffer = dmabuf->priv;
> +
> +	gen_pool_free(buffer->pool, (unsigned long)buffer->vaddr, buffer->len);
> +	kfree(buffer);
> +}
> +
> +static int dma_heap_mmap(struct dma_buf *dmabuf, struct vm_area_struct *vma)
> +{
> +	struct sram_dma_heap_buffer *buffer = dmabuf->priv;
> +	int ret;
> +
> +	/* SRAM mappings are not cached */
> +	vma->vm_page_prot = pgprot_writecombine(vma->vm_page_prot);
> +
> +	ret = vm_iomap_memory(vma, buffer->paddr, buffer->len);
> +	if (ret)
> +		pr_err("Could not map buffer to userspace\n");
> +
> +	return ret;
> +}
> +
> +static int dma_heap_vmap(struct dma_buf *dmabuf, struct iosys_map *map)
> +{
> +	struct sram_dma_heap_buffer *buffer = dmabuf->priv;
> +
> +	iosys_map_set_vaddr(map, buffer->vaddr);
> +
> +	return 0;
> +}
> +
> +static const struct dma_buf_ops sram_dma_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,
> +	.release = dma_heap_dma_buf_release,
> +	.mmap = dma_heap_mmap,
> +	.vmap = dma_heap_vmap,
> +};
> +
> +static struct dma_buf *sram_dma_heap_allocate(struct dma_heap *heap,
> +					      unsigned long len,
> +					      unsigned long fd_flags,
> +					      unsigned long heap_flags)
> +{
> +	struct sram_dma_heap *sram_dma_heap = dma_heap_get_drvdata(heap);
> +	struct sram_dma_heap_buffer *buffer;
> +
> +	DEFINE_DMA_BUF_EXPORT_INFO(exp_info);
> +	struct dma_buf *dmabuf;
> +	int ret = 0;
> +
> +	buffer = kzalloc(sizeof(*buffer), GFP_KERNEL);
> +	if (!buffer)
> +		return ERR_PTR(-ENOMEM);
> +	buffer->pool = sram_dma_heap->pool;
> +	INIT_LIST_HEAD(&buffer->attachments);
> +	mutex_init(&buffer->attachments_lock);
> +	buffer->len = len;
> +
> +	buffer->vaddr = (void *)gen_pool_alloc(buffer->pool, buffer->len);
> +	if (!buffer->vaddr) {
> +		ret = -ENOMEM;
> +		goto free_buffer;
> +	}
> +
> +	buffer->paddr = gen_pool_virt_to_phys(buffer->pool, (unsigned long)buffer->vaddr);
> +	if (buffer->paddr == -1) {
> +		ret = -ENOMEM;
> +		goto free_pool;
> +	}
> +
> +	/* create the dmabuf */
> +	exp_info.exp_name = dma_heap_get_name(heap);
> +	exp_info.ops = &sram_dma_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_pool;
> +	}
> +
> +	return dmabuf;
> +
> +free_pool:
> +	gen_pool_free(buffer->pool, (unsigned long)buffer->vaddr, buffer->len);
> +free_buffer:
> +	kfree(buffer);
> +
> +	return ERR_PTR(ret);
> +}
> +
> +static struct dma_heap_ops sram_dma_heap_ops = {
> +	.allocate = sram_dma_heap_allocate,
> +};
> +
> +int sram_add_dma_heap(struct sram_dev *sram,
> +		      struct sram_reserve *block,
> +		      phys_addr_t start,
> +		      struct sram_partition *part)
> +{
> +	struct sram_dma_heap *sram_dma_heap;
> +	struct dma_heap_export_info exp_info;
> +
> +	dev_info(sram->dev, "Exporting SRAM Heap '%s'\n", block->label);
> +
> +	sram_dma_heap = kzalloc(sizeof(*sram_dma_heap), GFP_KERNEL);
> +	if (!sram_dma_heap)
> +		return -ENOMEM;
> +	sram_dma_heap->pool = part->pool;
> +
> +	exp_info.name = kasprintf(GFP_KERNEL, "sram_%s", block->label);
> +	exp_info.ops = &sram_dma_heap_ops;
> +	exp_info.priv = sram_dma_heap;
> +	sram_dma_heap->heap = dma_heap_add(&exp_info);
> +	if (IS_ERR(sram_dma_heap->heap)) {
> +		int ret = PTR_ERR(sram_dma_heap->heap);
> +		kfree(sram_dma_heap);
> +		return ret;
> +	}
> +
> +	return 0;
> +}
> diff --git a/drivers/misc/sram.c b/drivers/misc/sram.c
> index 5757adf418b1d..6dd173a2fba8e 100644
> --- a/drivers/misc/sram.c
> +++ b/drivers/misc/sram.c
> @@ -120,6 +120,12 @@ static int sram_add_partition(struct sram_dev *sram, struct sram_reserve *block,
>   		ret = sram_add_pool(sram, block, start, part);
>   		if (ret)
>   			return ret;
> +
> +		if (block->export) {
> +			ret = sram_add_dma_heap(sram, block, start, part);
> +			if (ret)
> +				return ret;
> +		}
>   	}
>   	if (block->export) {
>   		ret = sram_add_export(sram, block, start, part);
> diff --git a/drivers/misc/sram.h b/drivers/misc/sram.h
> index 397205b8bf6ff..062bdd25fa068 100644
> --- a/drivers/misc/sram.h
> +++ b/drivers/misc/sram.h
> @@ -60,4 +60,20 @@ static inline int sram_add_protect_exec(struct sram_partition *part)
>   	return -ENODEV;
>   }
>   #endif /* CONFIG_SRAM_EXEC */
> +
> +#ifdef CONFIG_SRAM_DMA_HEAP
> +int sram_add_dma_heap(struct sram_dev *sram,
> +		      struct sram_reserve *block,
> +		      phys_addr_t start,
> +		      struct sram_partition *part);
> +#else
> +static inline int sram_add_dma_heap(struct sram_dev *sram,
> +				    struct sram_reserve *block,
> +				    phys_addr_t start,
> +				    struct sram_partition *part)
> +{
> +	return 0;
> +}
> +#endif /* CONFIG_SRAM_DMA_HEAP */
> +
>   #endif /* __SRAM_H */

Patch

diff --git a/drivers/misc/Kconfig b/drivers/misc/Kconfig
index 75e427f124b28..ee34dfb61605f 100644
--- a/drivers/misc/Kconfig
+++ b/drivers/misc/Kconfig
@@ -448,6 +448,13 @@  config SRAM
 config SRAM_EXEC
 	bool
 
+config SRAM_DMA_HEAP
+	bool "Export on-chip SRAM pools using DMA-Heaps"
+	depends on DMABUF_HEAPS && SRAM
+	help
+	  This driver allows the export of on-chip SRAM marked as both pool
+	  and exportable to userspace using the DMA-Heaps interface.
+
 config DW_XDATA_PCIE
 	depends on PCI
 	tristate "Synopsys DesignWare xData PCIe driver"
diff --git a/drivers/misc/Makefile b/drivers/misc/Makefile
index f2a4d1ff65d46..5e7516bfaa8de 100644
--- a/drivers/misc/Makefile
+++ b/drivers/misc/Makefile
@@ -47,6 +47,7 @@  obj-$(CONFIG_VMWARE_VMCI)	+= vmw_vmci/
 obj-$(CONFIG_LATTICE_ECP3_CONFIG)	+= lattice-ecp3-config.o
 obj-$(CONFIG_SRAM)		+= sram.o
 obj-$(CONFIG_SRAM_EXEC)		+= sram-exec.o
+obj-$(CONFIG_SRAM_DMA_HEAP)	+= sram-dma-heap.o
 obj-$(CONFIG_GENWQE)		+= genwqe/
 obj-$(CONFIG_ECHO)		+= echo/
 obj-$(CONFIG_CXL_BASE)		+= cxl/
diff --git a/drivers/misc/sram-dma-heap.c b/drivers/misc/sram-dma-heap.c
new file mode 100644
index 0000000000000..c054c04dff33e
--- /dev/null
+++ b/drivers/misc/sram-dma-heap.c
@@ -0,0 +1,245 @@ 
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * SRAM DMA-Heap userspace exporter
+ *
+ * Copyright (C) 2019-2022 Texas Instruments Incorporated - https://www.ti.com/
+ *	Andrew Davis <[e-mail]>
+ */
+
+#include <linux/dma-mapping.h>
+#include <linux/err.h>
+#include <linux/genalloc.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>
+
+#include "sram.h"
+
+struct sram_dma_heap {
+	struct dma_heap *heap;
+	struct gen_pool *pool;
+};
+
+struct sram_dma_heap_buffer {
+	struct gen_pool *pool;
+	struct list_head attachments;
+	struct mutex attachments_lock;
+	unsigned long len;
+	void *vaddr;
+	phys_addr_t paddr;
+};
+
+struct dma_heap_attachment {
+	struct device *dev;
+	struct sg_table *table;
+	struct list_head list;
+};
+
+static int dma_heap_attach(struct dma_buf *dmabuf,
+			   struct dma_buf_attachment *attachment)
+{
+	struct sram_dma_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 = kmalloc(sizeof(*table), GFP_KERNEL);
+	if (!table) {
+		kfree(a);
+		return -ENOMEM;
+	}
+	if (sg_alloc_table(table, 1, GFP_KERNEL)) {
+		kfree(table);
+		kfree(a);
+		return -ENOMEM;
+	}
+	sg_set_page(table->sgl, pfn_to_page(PFN_DOWN(buffer->paddr)), buffer->len, 0);
+
+	a->table = table;
+	a->dev = attachment->dev;
+	INIT_LIST_HEAD(&a->list);
+
+	attachment->priv = a;
+
+	mutex_lock(&buffer->attachments_lock);
+	list_add(&a->list, &buffer->attachments);
+	mutex_unlock(&buffer->attachments_lock);
+
+	return 0;
+}
+
+static void dma_heap_detatch(struct dma_buf *dmabuf,
+			     struct dma_buf_attachment *attachment)
+{
+	struct sram_dma_heap_buffer *buffer = dmabuf->priv;
+	struct dma_heap_attachment *a = attachment->priv;
+
+	mutex_lock(&buffer->attachments_lock);
+	list_del(&a->list);
+	mutex_unlock(&buffer->attachments_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;
+
+	/*
+	 * As this heap is backed by uncached SRAM memory we do not need to
+	 * perform any sync operations on the buffer before allowing device
+	 * domain access. For this reason we use SKIP_CPU_SYNC and also do
+	 * not use or provide begin/end_cpu_access() dma-buf functions.
+	 */
+	if (!dma_map_sg_attrs(attachment->dev, table->sgl, table->nents,
+			      direction, DMA_ATTR_SKIP_CPU_SYNC))
+		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);
+}
+
+static void dma_heap_dma_buf_release(struct dma_buf *dmabuf)
+{
+	struct sram_dma_heap_buffer *buffer = dmabuf->priv;
+
+	gen_pool_free(buffer->pool, (unsigned long)buffer->vaddr, buffer->len);
+	kfree(buffer);
+}
+
+static int dma_heap_mmap(struct dma_buf *dmabuf, struct vm_area_struct *vma)
+{
+	struct sram_dma_heap_buffer *buffer = dmabuf->priv;
+	int ret;
+
+	/* SRAM mappings are not cached */
+	vma->vm_page_prot = pgprot_writecombine(vma->vm_page_prot);
+
+	ret = vm_iomap_memory(vma, buffer->paddr, buffer->len);
+	if (ret)
+		pr_err("Could not map buffer to userspace\n");
+
+	return ret;
+}
+
+static int dma_heap_vmap(struct dma_buf *dmabuf, struct iosys_map *map)
+{
+	struct sram_dma_heap_buffer *buffer = dmabuf->priv;
+
+	iosys_map_set_vaddr(map, buffer->vaddr);
+
+	return 0;
+}
+
+static const struct dma_buf_ops sram_dma_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,
+	.release = dma_heap_dma_buf_release,
+	.mmap = dma_heap_mmap,
+	.vmap = dma_heap_vmap,
+};
+
+static struct dma_buf *sram_dma_heap_allocate(struct dma_heap *heap,
+					      unsigned long len,
+					      unsigned long fd_flags,
+					      unsigned long heap_flags)
+{
+	struct sram_dma_heap *sram_dma_heap = dma_heap_get_drvdata(heap);
+	struct sram_dma_heap_buffer *buffer;
+
+	DEFINE_DMA_BUF_EXPORT_INFO(exp_info);
+	struct dma_buf *dmabuf;
+	int ret = 0;
+
+	buffer = kzalloc(sizeof(*buffer), GFP_KERNEL);
+	if (!buffer)
+		return ERR_PTR(-ENOMEM);
+	buffer->pool = sram_dma_heap->pool;
+	INIT_LIST_HEAD(&buffer->attachments);
+	mutex_init(&buffer->attachments_lock);
+	buffer->len = len;
+
+	buffer->vaddr = (void *)gen_pool_alloc(buffer->pool, buffer->len);
+	if (!buffer->vaddr) {
+		ret = -ENOMEM;
+		goto free_buffer;
+	}
+
+	buffer->paddr = gen_pool_virt_to_phys(buffer->pool, (unsigned long)buffer->vaddr);
+	if (buffer->paddr == -1) {
+		ret = -ENOMEM;
+		goto free_pool;
+	}
+
+	/* create the dmabuf */
+	exp_info.exp_name = dma_heap_get_name(heap);
+	exp_info.ops = &sram_dma_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_pool;
+	}
+
+	return dmabuf;
+
+free_pool:
+	gen_pool_free(buffer->pool, (unsigned long)buffer->vaddr, buffer->len);
+free_buffer:
+	kfree(buffer);
+
+	return ERR_PTR(ret);
+}
+
+static struct dma_heap_ops sram_dma_heap_ops = {
+	.allocate = sram_dma_heap_allocate,
+};
+
+int sram_add_dma_heap(struct sram_dev *sram,
+		      struct sram_reserve *block,
+		      phys_addr_t start,
+		      struct sram_partition *part)
+{
+	struct sram_dma_heap *sram_dma_heap;
+	struct dma_heap_export_info exp_info;
+
+	dev_info(sram->dev, "Exporting SRAM Heap '%s'\n", block->label);
+
+	sram_dma_heap = kzalloc(sizeof(*sram_dma_heap), GFP_KERNEL);
+	if (!sram_dma_heap)
+		return -ENOMEM;
+	sram_dma_heap->pool = part->pool;
+
+	exp_info.name = kasprintf(GFP_KERNEL, "sram_%s", block->label);
+	exp_info.ops = &sram_dma_heap_ops;
+	exp_info.priv = sram_dma_heap;
+	sram_dma_heap->heap = dma_heap_add(&exp_info);
+	if (IS_ERR(sram_dma_heap->heap)) {
+		int ret = PTR_ERR(sram_dma_heap->heap);
+		kfree(sram_dma_heap);
+		return ret;
+	}
+
+	return 0;
+}
diff --git a/drivers/misc/sram.c b/drivers/misc/sram.c
index 5757adf418b1d..6dd173a2fba8e 100644
--- a/drivers/misc/sram.c
+++ b/drivers/misc/sram.c
@@ -120,6 +120,12 @@  static int sram_add_partition(struct sram_dev *sram, struct sram_reserve *block,
 		ret = sram_add_pool(sram, block, start, part);
 		if (ret)
 			return ret;
+
+		if (block->export) {
+			ret = sram_add_dma_heap(sram, block, start, part);
+			if (ret)
+				return ret;
+		}
 	}
 	if (block->export) {
 		ret = sram_add_export(sram, block, start, part);
diff --git a/drivers/misc/sram.h b/drivers/misc/sram.h
index 397205b8bf6ff..062bdd25fa068 100644
--- a/drivers/misc/sram.h
+++ b/drivers/misc/sram.h
@@ -60,4 +60,20 @@  static inline int sram_add_protect_exec(struct sram_partition *part)
 	return -ENODEV;
 }
 #endif /* CONFIG_SRAM_EXEC */
+
+#ifdef CONFIG_SRAM_DMA_HEAP
+int sram_add_dma_heap(struct sram_dev *sram,
+		      struct sram_reserve *block,
+		      phys_addr_t start,
+		      struct sram_partition *part);
+#else
+static inline int sram_add_dma_heap(struct sram_dev *sram,
+				    struct sram_reserve *block,
+				    phys_addr_t start,
+				    struct sram_partition *part)
+{
+	return 0;
+}
+#endif /* CONFIG_SRAM_DMA_HEAP */
+
 #endif /* __SRAM_H */