Re: [PATCHv3 13/22] staging: android: ion: Use CMA APIs directly

[Laura Abbott]

On 04/10/2017 11:47 PM, Laurent Pinchart wrote:
> Hi Laura,
> 
> Thank you for the patch.
> 
> On Monday 03 Apr 2017 11:57:55 Laura Abbott wrote:
>> When CMA was first introduced, its primary use was for DMA allocation
>> and the only way to get CMA memory was to call dma_alloc_coherent. This
>> put Ion in an awkward position since there was no device structure
>> readily available and setting one up messed up the coherency model.
>> These days, CMA can be allocated directly from the APIs. Switch to using
>> this model to avoid needing a dummy device. This also mitigates some of
>> the caching problems (e.g. dma_alloc_coherent only returning uncached
>> memory).
> 
> Do we have a guarantee that the DMA mapping API, which we have to use for 
> cache handling, will always support memory we allocate directly from CMA 
> behind its back ?
> 

CMA pages are no different than other pages allocated via the buddy
allocator. There should be no issue passing that memory to the
streaming API.

Thanks,
Laura

>> Signed-off-by: Laura Abbott <labbott@xxxxxxxxxx>
>> ---
>>  drivers/staging/android/ion/Kconfig        |  7 +++
>>  drivers/staging/android/ion/Makefile       |  3 +-
>>  drivers/staging/android/ion/ion_cma_heap.c | 97 +++++++--------------------
>>  3 files changed, 35 insertions(+), 72 deletions(-)
>>
>> diff --git a/drivers/staging/android/ion/Kconfig
>> b/drivers/staging/android/ion/Kconfig index 206c4de..15108c4 100644
>> --- a/drivers/staging/android/ion/Kconfig
>> +++ b/drivers/staging/android/ion/Kconfig
>> @@ -10,3 +10,10 @@ menuconfig ION
>>  	  If you're not using Android its probably safe to
>>  	  say N here.
>>
>> +config ION_CMA_HEAP
>> +	bool "Ion CMA heap support"
>> +	depends on ION && CMA
>> +	help
>> +	  Choose this option to enable CMA heaps with Ion. This heap is backed
>> +	  by the Contiguous Memory Allocator (CMA). If your system has these
>> +	  regions, you should say Y here.
>> diff --git a/drivers/staging/android/ion/Makefile
>> b/drivers/staging/android/ion/Makefile index 26672a0..66d0c4a 100644
>> --- a/drivers/staging/android/ion/Makefile
>> +++ b/drivers/staging/android/ion/Makefile
>> @@ -1,6 +1,7 @@
>>  obj-$(CONFIG_ION) +=	ion.o ion-ioctl.o ion_heap.o \
>>  			ion_page_pool.o ion_system_heap.o \
>> -			ion_carveout_heap.o ion_chunk_heap.o ion_cma_heap.o
>> +			ion_carveout_heap.o ion_chunk_heap.o
>> +obj-$(CONFIG_ION_CMA_HEAP) += ion_cma_heap.o
>>  ifdef CONFIG_COMPAT
>>  obj-$(CONFIG_ION) += compat_ion.o
>>  endif
>> diff --git a/drivers/staging/android/ion/ion_cma_heap.c
>> b/drivers/staging/android/ion/ion_cma_heap.c index d562fd7..f3e0f59 100644
>> --- a/drivers/staging/android/ion/ion_cma_heap.c
>> +++ b/drivers/staging/android/ion/ion_cma_heap.c
>> @@ -19,24 +19,19 @@
>>  #include <linux/slab.h>
>>  #include <linux/errno.h>
>>  #include <linux/err.h>
>> -#include <linux/dma-mapping.h>
>> +#include <linux/cma.h>
>> +#include <linux/scatterlist.h>
>>
>>  #include "ion.h"
>>  #include "ion_priv.h"
>>
>>  struct ion_cma_heap {
>>  	struct ion_heap heap;
>> -	struct device *dev;
>> +	struct cma *cma;
>>  };
>>
>>  #define to_cma_heap(x) container_of(x, struct ion_cma_heap, heap)
>>
>> -struct ion_cma_buffer_info {
>> -	void *cpu_addr;
>> -	dma_addr_t handle;
>> -	struct sg_table *table;
>> -};
>> -
>>
>>  /* ION CMA heap operations functions */
>>  static int ion_cma_allocate(struct ion_heap *heap, struct ion_buffer
>> *buffer, @@ -44,93 +39,53 @@ static int ion_cma_allocate(struct ion_heap
>> *heap, struct ion_buffer *buffer, unsigned long flags)
>>  {
>>  	struct ion_cma_heap *cma_heap = to_cma_heap(heap);
>> -	struct device *dev = cma_heap->dev;
>> -	struct ion_cma_buffer_info *info;
>> -
>> -	dev_dbg(dev, "Request buffer allocation len %ld\n", len);
>> -
>> -	if (buffer->flags & ION_FLAG_CACHED)
>> -		return -EINVAL;
>> +	struct sg_table *table;
>> +	struct page *pages;
>> +	int ret;
>>
>> -	info = kzalloc(sizeof(*info), GFP_KERNEL);
>> -	if (!info)
>> +	pages = cma_alloc(cma_heap->cma, len, 0, GFP_KERNEL);
>> +	if (!pages)
>>  		return -ENOMEM;
>>
>> -	info->cpu_addr = dma_alloc_coherent(dev, len, &(info->handle),
>> -						GFP_HIGHUSER | __GFP_ZERO);
>> -
>> -	if (!info->cpu_addr) {
>> -		dev_err(dev, "Fail to allocate buffer\n");
>> +	table = kmalloc(sizeof(struct sg_table), GFP_KERNEL);
>> +	if (!table)
>>  		goto err;
>> -	}
>>
>> -	info->table = kmalloc(sizeof(*info->table), GFP_KERNEL);
>> -	if (!info->table)
>> +	ret = sg_alloc_table(table, 1, GFP_KERNEL);
>> +	if (ret)
>>  		goto free_mem;
>>
>> -	if (dma_get_sgtable(dev, info->table, info->cpu_addr, info->handle,
>> -			    len))
>> -		goto free_table;
>> -	/* keep this for memory release */
>> -	buffer->priv_virt = info;
>> -	buffer->sg_table = info->table;
>> -	dev_dbg(dev, "Allocate buffer %p\n", buffer);
>> +	sg_set_page(table->sgl, pages, len, 0);
>> +
>> +	buffer->priv_virt = pages;
>> +	buffer->sg_table = table;
>>  	return 0;
>>
>> -free_table:
>> -	kfree(info->table);
>>  free_mem:
>> -	dma_free_coherent(dev, len, info->cpu_addr, info->handle);
>> +	kfree(table);
>>  err:
>> -	kfree(info);
>> +	cma_release(cma_heap->cma, pages, buffer->size);
>>  	return -ENOMEM;
>>  }
>>
>>  static void ion_cma_free(struct ion_buffer *buffer)
>>  {
>>  	struct ion_cma_heap *cma_heap = to_cma_heap(buffer->heap);
>> -	struct device *dev = cma_heap->dev;
>> -	struct ion_cma_buffer_info *info = buffer->priv_virt;
>> +	struct page *pages = buffer->priv_virt;
>>
>> -	dev_dbg(dev, "Release buffer %p\n", buffer);
>>  	/* release memory */
>> -	dma_free_coherent(dev, buffer->size, info->cpu_addr, info->handle);
>> +	cma_release(cma_heap->cma, pages, buffer->size);
>>  	/* release sg table */
>> -	sg_free_table(info->table);
>> -	kfree(info->table);
>> -	kfree(info);
>> -}
>> -
>> -static int ion_cma_mmap(struct ion_heap *mapper, struct ion_buffer *buffer,
>> -			struct vm_area_struct *vma)
>> -{
>> -	struct ion_cma_heap *cma_heap = to_cma_heap(buffer->heap);
>> -	struct device *dev = cma_heap->dev;
>> -	struct ion_cma_buffer_info *info = buffer->priv_virt;
>> -
>> -	return dma_mmap_coherent(dev, vma, info->cpu_addr, info->handle,
>> -				 buffer->size);
>> -}
>> -
>> -static void *ion_cma_map_kernel(struct ion_heap *heap,
>> -				struct ion_buffer *buffer)
>> -{
>> -	struct ion_cma_buffer_info *info = buffer->priv_virt;
>> -	/* kernel memory mapping has been done at allocation time */
>> -	return info->cpu_addr;
>> -}
>> -
>> -static void ion_cma_unmap_kernel(struct ion_heap *heap,
>> -				 struct ion_buffer *buffer)
>> -{
>> +	sg_free_table(buffer->sg_table);
>> +	kfree(buffer->sg_table);
>>  }
>>
>>  static struct ion_heap_ops ion_cma_ops = {
>>  	.allocate = ion_cma_allocate,
>>  	.free = ion_cma_free,
>> -	.map_user = ion_cma_mmap,
>> -	.map_kernel = ion_cma_map_kernel,
>> -	.unmap_kernel = ion_cma_unmap_kernel,
>> +	.map_user = ion_heap_map_user,
>> +	.map_kernel = ion_heap_map_kernel,
>> +	.unmap_kernel = ion_heap_unmap_kernel,
>>  };
>>
>>  struct ion_heap *ion_cma_heap_create(struct ion_platform_heap *data)
>> @@ -147,7 +102,7 @@ struct ion_heap *ion_cma_heap_create(struct
>> ion_platform_heap *data) * get device from private heaps data, later it
>> will be
>>  	 * used to make the link with reserved CMA memory
>>  	 */
>> -	cma_heap->dev = data->priv;
>> +	cma_heap->cma = data->priv;
>>  	cma_heap->heap.type = ION_HEAP_TYPE_DMA;
>>  	return &cma_heap->heap;
>>  }
>