[3/3] uio: Add UIO_DMABUF_HEAP

Some UIO users need to access DMA addresses from userspace to be able to
configure DMA done by the UIO device. Currently there is no way of doing
this.

Add a UIO_DMABUF_HEAP Kconfig option. When selected, a dma-heap
allocator is created for every new UIO device. This allocator only
implements 4 basic operations: allocate, release, mmap and get_dma_addr.
The buffer allocation is done through dma_alloc_coherent().

Signed-off-by: Bastien Curutchet <bastien.curutchet@bootlin.com>
---
 drivers/uio/Kconfig        |   9 ++++
 drivers/uio/Makefile       |   1 +
 drivers/uio/uio.c          |   4 ++
 drivers/uio/uio_heap.c     | 120 +++++++++++++++++++++++++++++++++++++++++++++
 include/linux/uio_driver.h |   2 +
 5 files changed, 136 insertions(+)

Hi Bastien,

Le jeudi 10 avril 2025 à 16:53 +0200, Bastien Curutchet a écrit :
> Some UIO users need to access DMA addresses from userspace to be able to
> configure DMA done by the UIO device. Currently there is no way of doing
> this.
> 
> Add a UIO_DMABUF_HEAP Kconfig option. When selected, a dma-heap
> allocator is created for every new UIO device. This allocator only
> implements 4 basic operations: allocate, release, mmap and get_dma_addr.
> The buffer allocation is done through dma_alloc_coherent().

This is quite redundant with the CMA heap. I believe a better design is
to make UIO devices dmabuf importers. This will make your UIO dmabuf
implementation a lot more useful.

As for the physical addresses, everywhere you currently pass a physical
address, you should be able to add ioctl to pass a DMABuf FD, or a
handle to an UIO specific object (similar to buffer objects in DRM) and
hide these.

regards,
Nicolas

> 
> Signed-off-by: Bastien Curutchet <bastien.curutchet@bootlin.com>
> ---
>  drivers/uio/Kconfig        |   9 ++++
>  drivers/uio/Makefile       |   1 +
>  drivers/uio/uio.c          |   4 ++
>  drivers/uio/uio_heap.c     | 120 +++++++++++++++++++++++++++++++++++++++++++++
>  include/linux/uio_driver.h |   2 +
>  5 files changed, 136 insertions(+)
> 
> diff --git a/drivers/uio/Kconfig b/drivers/uio/Kconfig
> index b060dcd7c6350191726c0830a1ae7b9a388ca4bb..2f3b1e57fceb01354b65cc4d39f342f645a238db 100644
> --- a/drivers/uio/Kconfig
> +++ b/drivers/uio/Kconfig
> @@ -164,4 +164,13 @@ config UIO_DFL
>  	    opae-sdk/tools/libopaeuio/
>  
>  	  If you compile this as a module, it will be called uio_dfl.
> +
> +config UIO_DMABUF_HEAP
> +	bool "DMA-BUF UIO Heap"
> +	select DMABUF_HEAPS
> +	help
> +	  Choose this option to enable DMA-BUF UIO heap. It will create a new
> +	  heap allocator under /dev/dma_heap/ for every UIO device. This
> +	  allocator allows userspace applications to allocate DMA buffers and
> +	  access their DMA addresses thanks to the DMA_BUF_IOCTL_GET_DMA_HANDLE
>  endif
> diff --git a/drivers/uio/Makefile b/drivers/uio/Makefile
> index 1c5f3b5a95cf5b681a843b745a046d7ce123255d..f6696daa36567a4e5d18b1b89ba688057e758400 100644
> --- a/drivers/uio/Makefile
> +++ b/drivers/uio/Makefile
> @@ -11,3 +11,4 @@ obj-$(CONFIG_UIO_MF624)         += uio_mf624.o
>  obj-$(CONFIG_UIO_FSL_ELBC_GPCM)	+= uio_fsl_elbc_gpcm.o
>  obj-$(CONFIG_UIO_HV_GENERIC)	+= uio_hv_generic.o
>  obj-$(CONFIG_UIO_DFL)	+= uio_dfl.o
> +obj-$(CONFIG_UIO_DMABUF_HEAP) += uio_heap.o
> diff --git a/drivers/uio/uio.c b/drivers/uio/uio.c
> index d93ed4e86a174b5bad193a61aa522cd833fe7bb5..f31936a897805a284165cccfee3d66e96acd4b39 100644
> --- a/drivers/uio/uio.c
> +++ b/drivers/uio/uio.c
> @@ -1046,7 +1046,11 @@ int __uio_register_device(struct module *owner,
>  		}
>  	}
>  
> +#if defined(CONFIG_UIO_DMABUF_HEAP)
> +	return add_uio_heap(idev);
> +#else
>  	return 0;
> +#endif
>  
>  err_request_irq:
>  	uio_dev_del_attributes(idev);
> diff --git a/drivers/uio/uio_heap.c b/drivers/uio/uio_heap.c
> new file mode 100644
> index 0000000000000000000000000000000000000000..2e836b503458e280babba0e0adc4f6d8344efc82
> --- /dev/null
> +++ b/drivers/uio/uio_heap.c
> @@ -0,0 +1,120 @@
> +// SPDX-License-Identifier: GPL-2.0
> +#include <linux/dma-buf.h>
> +#include <linux/dma-heap.h>
> +#include <linux/uio_driver.h>
> +
> +struct uio_heap {
> +	struct dma_heap *heap;
> +	struct device *dev;
> +};
> +
> +struct uio_heap_buffer {
> +	struct uio_heap *heap;
> +	dma_addr_t dma_addr;
> +	unsigned long len;
> +	void *vaddr;
> +};
> +
> +static int uio_heap_mmap(struct dma_buf *dmabuf, struct vm_area_struct *vma)
> +{
> +	struct uio_heap_buffer *buffer = dmabuf->priv;
> +
> +	return dma_mmap_coherent(buffer->heap->dev, vma, buffer->vaddr,
> +				 buffer->dma_addr, buffer->len);
> +}
> +
> +static void uio_heap_dma_buf_release(struct dma_buf *dmabuf)
> +{
> +	struct uio_heap_buffer *buffer = dmabuf->priv;
> +
> +	dma_free_coherent(buffer->heap->dev, buffer->len, buffer->vaddr,
> +			  buffer->dma_addr);
> +	kfree(buffer);
> +}
> +
> +static int uio_heap_get_dma_addr(struct dma_buf *dmabuf, u64 *addr)
> +{
> +	struct uio_heap_buffer *buffer = dmabuf->priv;
> +
> +	*addr = buffer->dma_addr;
> +	return 0;
> +}
> +
> +static const struct dma_buf_ops uio_heap_buf_ops = {
> +	.mmap = uio_heap_mmap,
> +	.release = uio_heap_dma_buf_release,
> +	.get_dma_addr = uio_heap_get_dma_addr,
> +};
> +
> +static struct dma_buf *uio_heap_allocate(struct dma_heap *heap,
> +					 unsigned long len,
> +					 u32 fd_flags,
> +					 u64 heap_flags)
> +{
> +	struct uio_heap *uio_heap = dma_heap_get_drvdata(heap);
> +	DEFINE_DMA_BUF_EXPORT_INFO(exp_info);
> +	struct uio_heap_buffer *buffer;
> +	struct dma_buf *dmabuf;
> +
> +	buffer = kzalloc(sizeof(*buffer), GFP_KERNEL);
> +	if (!buffer)
> +		return ERR_PTR(-ENOMEM);
> +
> +	dma_set_coherent_mask(uio_heap->dev, DMA_BIT_MASK(32));
> +
> +	buffer->heap = uio_heap;
> +	buffer->len = len;
> +	buffer->vaddr = dma_alloc_coherent(uio_heap->dev, buffer->len,
> +					   &buffer->dma_addr, GFP_KERNEL);
> +	if (IS_ERR(buffer->vaddr))
> +		goto free_buf;
> +
> +	exp_info.exp_name = dma_heap_get_name(heap);
> +	exp_info.ops = &uio_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))
> +		goto free_dma;
> +
> +	return dmabuf;
> +
> +free_dma:
> +	dma_free_coherent(uio_heap->dev, buffer->len, buffer->vaddr, buffer->dma_addr);
> +free_buf:
> +	kfree(buffer);
> +
> +	return ERR_PTR(-ENOMEM);
> +}
> +
> +static const struct dma_heap_ops uio_heap_ops = {
> +	.allocate = uio_heap_allocate,
> +};
> +
> +int add_uio_heap(struct uio_device *uio)
> +{
> +	struct dma_heap_export_info exp_info;
> +	struct uio_heap *uio_heap;
> +
> +	uio_heap = kzalloc(sizeof(*uio_heap), GFP_KERNEL);
> +	if (!uio_heap)
> +		return -ENOMEM;
> +
> +	uio_heap->dev = &uio->dev;
> +
> +	/* Use device name as heap name */
> +	exp_info.name = uio_heap->dev->kobj.name;
> +	exp_info.ops = &uio_heap_ops;
> +	exp_info.priv = uio_heap;
> +
> +	uio_heap->heap = dma_heap_add(&exp_info);
> +	if (IS_ERR(uio_heap->heap)) {
> +		int ret = PTR_ERR(uio_heap->heap);
> +
> +		kfree(uio_heap);
> +		return ret;
> +	}
> +
> +	return 0;
> +}
> diff --git a/include/linux/uio_driver.h b/include/linux/uio_driver.h
> index 18238dc8bfd356a20996ba6cd84f1ff508bbb81c..f8b774d2fa1c7de4b6af881f1e53dfa9f25b3dbf 100644
> --- a/include/linux/uio_driver.h
> +++ b/include/linux/uio_driver.h
> @@ -143,6 +143,8 @@ extern int __must_check
>  				   struct device *parent,
>  				   struct uio_info *info);
>  
> +extern int add_uio_heap(struct uio_device *uio);
> +
>  /* use a define to avoid include chaining to get THIS_MODULE */
>  
>  /**