[RFC][PATCH] add dma_reserve_coherent_memory()/dma_free_reserved_memory() API

[Guennadi Liakhovetski]

On Thu, 19 Aug 2010, Marin Mitov wrote:

> Hi all,
> 
> struct device contains a member: struct dma_coherent_mem *dma_mem;
> to hold information for a piece of memory declared dma-coherent.
> Alternatively the same member could also be used to hold preallocated
> dma-coherent memory for latter per-device use.
> 
> This tric is already used in drivers/staging/dt3155v4l.c
> dt3155_alloc_coherent()/dt3155_free_coherent()
> 
> Here proposed for general use by popular demand from video4linux folks.
> Helps for videobuf-dma-contig framework.

Ok, so, we've got two solutions to this problem submitted on the same 
day;) Following this thread:

http://marc.info/?t=128128236400002&r=1&w=2

on the ARM Linux kernel ML, I submitted a patch series

http://thread.gmane.org/gmane.linux.ports.sh.devel/8595

with a couple of fixes and improvements, the actual new API and a use 
example. My approach is slightly different, in that instead of requiring 
drivers to issue two calls - one to reserve RAM (usually 
dma_alloc_coherent()) and one to assign it to a device, my patch follows 
the suggestion from Russell King from the first thread and unites these 
two operations. So, now we have a choice;) Unfortunately, these two patch 
series went to orthogonal sets of recepients, I'm trying to fix this by 
adding a couple of CC entries.

Thanks
Guennadi

> 
> Signed-off-by: Marin Mitov <mitov at issp.bas.bg>
> 
> ======================================================================
> --- a/drivers/base/dma-coherent.c	2010-08-19 15:50:42.000000000 +0300
> +++ b/drivers/base/dma-coherent.c	2010-08-19 17:27:56.000000000 +0300
> @@ -93,6 +93,83 @@ void *dma_mark_declared_memory_occupied(
>  EXPORT_SYMBOL(dma_mark_declared_memory_occupied);
>  
>  /**
> + * dma_reserve_coherent_memory() - reserve coherent memory for per-device use
> + *
> + * @dev:	device from which we allocate memory
> + * @size:	size of requested memory area in bytes
> + * @flags:	same as in dma_declare_coherent_memory()
> + *
> + * This function reserves coherent memory allocating it early (during probe())
> + * to support latter allocations from per-device coherent memory pools.
> + * For a given device one could use either dma_declare_coherent_memory() or
> + * dma_reserve_coherent_memory(), but not both, becase the result of these
> + * functions is stored in a single struct device member - dma_mem
> + *
> + * Returns DMA_MEMORY_MAP on success, or 0 if failed.
> + * (same as dma_declare_coherent_memory()
> + */
> +int dma_reserve_coherent_memory(struct device *dev, size_t size, int flags)
> +{
> +	struct dma_coherent_mem *mem;
> +	dma_addr_t dev_base;
> +	int pages = size >> PAGE_SHIFT;
> +	int bitmap_size = BITS_TO_LONGS(pages) * sizeof(long);
> +
> +	if ((flags & DMA_MEMORY_MAP) == 0)
> +		goto out;
> +	if (!size)
> +		goto out;
> +	if (dev->dma_mem)
> +		goto out;
> +
> +	mem = kzalloc(sizeof(*mem), GFP_KERNEL);
> +	if (!mem)
> +		goto out;
> +	mem->virt_base = dma_alloc_coherent(dev, size, &dev_base,
> +							DT3155_COH_FLAGS);
> +	if (!mem->virt_base)
> +		goto err_alloc_coherent;
> +	mem->bitmap = kzalloc(bitmap_size, GFP_KERNEL);
> +	if (!mem->bitmap)
> +		goto err_bitmap;
> +
> +	mem->device_base = dev_base;
> +	mem->size = pages;
> +	mem->flags = flags;
> +	dev->dma_mem = mem;
> +	return DMA_MEMORY_MAP;
> +
> +err_bitmap:
> +	dma_free_coherent(dev, size, mem->virt_base, dev_base);
> +err_alloc_coherent:
> +	kfree(mem);
> +out:
> +	return 0;
> +}
> +EXPORT_SYMBOL(dma_reserve_coherent_memory);
> +
> +/**
> + * dma_free_reserved_memory() - free the reserved dma-coherent memoty
> + *
> + * @dev:	device for which we free the dma-coherent memory
> + *
> + * same as dma_release_declared_memory()
> + */
> +void dma_free_reserved_memory(struct device *dev)
> +{
> +	struct dma_coherent_mem *mem = dev->dma_mem;
> +
> +	if (!mem)
> +		return;
> +	dev->dma_mem = NULL;
> +	dma_free_coherent(dev, mem->size << PAGE_SHIFT,
> +					mem->virt_base, mem->device_base);
> +	kfree(mem->bitmap);
> +	kfree(mem);
> +}
> +EXPORT_SYMBOL(dma_free_reserved_memory);
> +
> +/**
>   * dma_alloc_from_coherent() - try to allocate memory from the per-device coherent area
>   *
>   * @dev:	device from which we allocate memory
> --
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---
Guennadi Liakhovetski, Ph.D.
Freelance Open-Source Software Developer
http://www.open-technology.de/