Re: [PATCH v2 RESEND 3/4] drivers: dma-coherent: add initialization from device tree

[Marek Szyprowski <m.szyprowski@samsung.com>]

Hello,

On 2014-07-29 23:54, Grant Likely wrote:
> On Mon, 14 Jul 2014 10:28:06 +0200, Marek Szyprowski <m.szyprowski@samsung.com> wrote:
>> Initialization procedure of dma coherent pool has been split into two
>> parts, so memory pool can now be initialized without assigning to
>> particular struct device. Then initialized region can be assigned to
>> more than one struct device. To protect from concurent allocations from
>> different devices, a spinlock has been added to dma_coherent_mem
>> structure. The last part of this patch adds support for handling
>> 'shared-dma-pool' reserved-memory device tree nodes.
>>
>> Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
> I think this looks okay. It isn't in my area of expertise though.
> Comments below.
>
>> ---
>>   drivers/base/dma-coherent.c | 137 ++++++++++++++++++++++++++++++++++++++------
>>   1 file changed, 118 insertions(+), 19 deletions(-)
>>
>> diff --git a/drivers/base/dma-coherent.c b/drivers/base/dma-coherent.c
>> index 7d6e84a51424..7185a4f247e1 100644
>> --- a/drivers/base/dma-coherent.c
>> +++ b/drivers/base/dma-coherent.c
>> @@ -14,11 +14,14 @@ struct dma_coherent_mem {
>>   	int		size;
>>   	int		flags;
>>   	unsigned long	*bitmap;
>> +	spinlock_t	spinlock;
>>   };
>>   
>> -int dma_declare_coherent_memory(struct device *dev, phys_addr_t phys_addr,
>> -				dma_addr_t device_addr, size_t size, int flags)
>> +static int dma_init_coherent_memory(phys_addr_t phys_addr, dma_addr_t device_addr,
>> +			     size_t size, int flags,
>> +			     struct dma_coherent_mem **mem)
> This is a bit odd. Why wouldn't you return the dma_mem pointer directly
> instead of passing in a **mem argument?

Because this function (as a direct successor of 
dma_declare_coherent_memory) doesn't
return typical error codes, but some custom values like DMA_MEMORY_MAP, 
DMA_MEMORY_IO
or zero (which means failure). I wanted to avoid confusion with typical 
error
handling path and IS_ERR/ERR_PTR usage used widely in other functions. 
This probably
should be unified with the rest of kernel some day, but right now I 
wanted to keep
the patch simple and easy to review.

>>   {
>> +	struct dma_coherent_mem *dma_mem = NULL;
>>   	void __iomem *mem_base = NULL;
>>   	int pages = size >> PAGE_SHIFT;
>>   	int bitmap_size = BITS_TO_LONGS(pages) * sizeof(long);
>> @@ -27,27 +30,26 @@ int dma_declare_coherent_memory(struct device *dev, phys_addr_t phys_addr,
>>   		goto out;
>>   	if (!size)
>>   		goto out;
>> -	if (dev->dma_mem)
>> -		goto out;
>> -
>> -	/* FIXME: this routine just ignores DMA_MEMORY_INCLUDES_CHILDREN */
>>   
>>   	mem_base = ioremap(phys_addr, size);
>>   	if (!mem_base)
>>   		goto out;
>>   
>> -	dev->dma_mem = kzalloc(sizeof(struct dma_coherent_mem), GFP_KERNEL);
>> -	if (!dev->dma_mem)
>> +	dma_mem = kzalloc(sizeof(struct dma_coherent_mem), GFP_KERNEL);
>> +	if (!dma_mem)
>>   		goto out;
>> -	dev->dma_mem->bitmap = kzalloc(bitmap_size, GFP_KERNEL);
>> -	if (!dev->dma_mem->bitmap)
>> +	dma_mem->bitmap = kzalloc(bitmap_size, GFP_KERNEL);
>> +	if (!dma_mem->bitmap)
>>   		goto free1_out;
>>   
>> -	dev->dma_mem->virt_base = mem_base;
>> -	dev->dma_mem->device_base = device_addr;
>> -	dev->dma_mem->pfn_base = PFN_DOWN(phys_addr);
>> -	dev->dma_mem->size = pages;
>> -	dev->dma_mem->flags = flags;
>> +	dma_mem->virt_base = mem_base;
>> +	dma_mem->device_base = device_addr;
>> +	dma_mem->pfn_base = PFN_DOWN(phys_addr);
>> +	dma_mem->size = pages;
>> +	dma_mem->flags = flags;
>> +	spin_lock_init(&dma_mem->spinlock);
>> +
>> +	*mem = dma_mem;
>>   
>>   	if (flags & DMA_MEMORY_MAP)
>>   		return DMA_MEMORY_MAP;
>> @@ -55,12 +57,51 @@ int dma_declare_coherent_memory(struct device *dev, phys_addr_t phys_addr,
>>   	return DMA_MEMORY_IO;
>>   
>>    free1_out:
>> -	kfree(dev->dma_mem);
>> +	kfree(dma_mem);
>>    out:
>>   	if (mem_base)
>>   		iounmap(mem_base);
>>   	return 0;
>>   }
>> +
>> +static void dma_release_coherent_memory(struct dma_coherent_mem *mem)
>> +{
>> +	if (!mem)
>> +		return;
>> +	iounmap(mem->virt_base);
>> +	kfree(mem->bitmap);
>> +	kfree(mem);
>> +}
>> +
>> +static int dma_assign_coherent_memory(struct device *dev,
>> +				      struct dma_coherent_mem *mem)
>> +{
>> +	if (dev->dma_mem)
>> +		return -EBUSY;
>> +
>> +	dev->dma_mem = mem;
>> +	/* FIXME: this routine just ignores DMA_MEMORY_INCLUDES_CHILDREN */
>> +
>> +	return 0;
>> +}
>> +
>> +int dma_declare_coherent_memory(struct device *dev, phys_addr_t phys_addr,
>> +				dma_addr_t device_addr, size_t size, int flags)
>> +{
>> +	struct dma_coherent_mem *mem;
>> +	int ret;
>> +
>> +	ret = dma_init_coherent_memory(phys_addr, device_addr, size, flags,
>> +				       &mem);
>> +	if (ret == 0)
>> +		return 0;
>> +
>> +	if (dma_assign_coherent_memory(dev, mem) == 0)
>> +		return ret;
>> +
>> +	dma_release_coherent_memory(mem);
>> +	return 0;
>> +}
>>   EXPORT_SYMBOL(dma_declare_coherent_memory);
>>   
>>   void dma_release_declared_memory(struct device *dev)
>> @@ -69,10 +110,8 @@ void dma_release_declared_memory(struct device *dev)
>>   
>>   	if (!mem)
>>   		return;
>> +	dma_release_coherent_memory(mem);
>>   	dev->dma_mem = NULL;
>> -	iounmap(mem->virt_base);
>> -	kfree(mem->bitmap);
>> -	kfree(mem);
>>   }
>>   EXPORT_SYMBOL(dma_release_declared_memory);
>>   
>> @@ -80,6 +119,7 @@ void *dma_mark_declared_memory_occupied(struct device *dev,
>>   					dma_addr_t device_addr, size_t size)
>>   {
>>   	struct dma_coherent_mem *mem = dev->dma_mem;
>> +	unsigned long flags;
>>   	int pos, err;
>>   
>>   	size += device_addr & ~PAGE_MASK;
>> @@ -87,8 +127,11 @@ void *dma_mark_declared_memory_occupied(struct device *dev,
>>   	if (!mem)
>>   		return ERR_PTR(-EINVAL);
>>   
>> +	spin_lock_irqsave(&mem->spinlock, flags);
>>   	pos = (device_addr - mem->device_base) >> PAGE_SHIFT;
>>   	err = bitmap_allocate_region(mem->bitmap, pos, get_order(size));
>> +	spin_unlock_irqrestore(&mem->spinlock, flags);
>> +
>>   	if (err != 0)
>>   		return ERR_PTR(err);
>>   	return mem->virt_base + (pos << PAGE_SHIFT);
>> @@ -115,6 +158,7 @@ int dma_alloc_from_coherent(struct device *dev, ssize_t size,
>>   {
>>   	struct dma_coherent_mem *mem;
>>   	int order = get_order(size);
>> +	unsigned long flags;
>>   	int pageno;
>>   
>>   	if (!dev)
>> @@ -124,6 +168,7 @@ int dma_alloc_from_coherent(struct device *dev, ssize_t size,
>>   		return 0;
>>   
>>   	*ret = NULL;
>> +	spin_lock_irqsave(&mem->spinlock, flags);
>>   
>>   	if (unlikely(size > (mem->size << PAGE_SHIFT)))
>>   		goto err;
>> @@ -138,10 +183,12 @@ int dma_alloc_from_coherent(struct device *dev, ssize_t size,
>>   	*dma_handle = mem->device_base + (pageno << PAGE_SHIFT);
>>   	*ret = mem->virt_base + (pageno << PAGE_SHIFT);
>>   	memset(*ret, 0, size);
>> +	spin_unlock_irqrestore(&mem->spinlock, flags);
>>   
>>   	return 1;
>>   
>>   err:
>> +	spin_unlock_irqrestore(&mem->spinlock, flags);
>>   	/*
>>   	 * In the case where the allocation can not be satisfied from the
>>   	 * per-device area, try to fall back to generic memory if the
>> @@ -171,8 +218,11 @@ int dma_release_from_coherent(struct device *dev, int order, void *vaddr)
>>   	if (mem && vaddr >= mem->virt_base && vaddr <
>>   		   (mem->virt_base + (mem->size << PAGE_SHIFT))) {
>>   		int page = (vaddr - mem->virt_base) >> PAGE_SHIFT;
>> +		unsigned long flags;
>>   
>> +		spin_lock_irqsave(&mem->spinlock, flags);
>>   		bitmap_release_region(mem->bitmap, page, order);
>> +		spin_unlock_irqrestore(&mem->spinlock, flags);
>>   		return 1;
>>   	}
>>   	return 0;
>> @@ -218,3 +268,52 @@ int dma_mmap_from_coherent(struct device *dev, struct vm_area_struct *vma,
>>   	return 0;
>>   }
>>   EXPORT_SYMBOL(dma_mmap_from_coherent);
>> +
>> +/*
>> + * Support for reserved memory regions defined in device tree
>> + */
>> +#ifdef CONFIG_OF_RESERVED_MEM
>> +#include <linux/of.h>
>> +#include <linux/of_fdt.h>
>> +#include <linux/of_reserved_mem.h>
>> +
>> +static void rmem_dma_device_init(struct reserved_mem *rmem, struct device *dev)
>> +{
>> +	struct dma_coherent_mem *mem = rmem->priv;
> Will the reserved_mem->priv pointer ever point to some other kind of
> structure? How do we know that the pointer here is always a
> dma_coherent_mem struct (if there are other uses of priv, what is the
> guarantee against another user assigning something to it?) Is it the
> reserved_mem_ops below that provide the guarantee?

reserved_mem_ops are set by the given reserved memory driver and access 
to priv
pointer is limited only to that driver. This pattern is used widely 
across the
whole kernel, so I don't think that a separate pointer to particular 
structure
type is needed.

> If it is a risk, then the alternative would be to put an explicit
> dma_coherent_mem pointer into the reserved_mem structure.

If one messes with priv pointers, he should expect serious problems and 
we really
cannot prevent him anyway.

>> +	if (!mem &&
>> +	    dma_init_coherent_memory(rmem->base, rmem->base, rmem->size,
>> +				     DMA_MEMORY_MAP | DMA_MEMORY_EXCLUSIVE,
>> +				     &mem) != DMA_MEMORY_MAP) {
>> +		pr_info("Reserved memory: failed to init DMA memory pool at %pa, size %ld MiB\n",
>> +			&rmem->base, (unsigned long)rmem->size / SZ_1M);
>> +		return;
>> +	}
>> +	rmem->priv = mem;
>> +	dma_assign_coherent_memory(dev, mem);
>> +}
>> +
>> +static void rmem_dma_device_release(struct reserved_mem *rmem,
>> +				    struct device *dev)
>> +{
>> +	dev->dma_mem = NULL;
>> +}
>> +
>> +static const struct reserved_mem_ops rmem_dma_ops = {
>> +	.device_init	= rmem_dma_device_init,
>> +	.device_release	= rmem_dma_device_release,
>> +};
>> +
>> +static int __init rmem_dma_setup(struct reserved_mem *rmem)
>> +{
>> +	unsigned long node = rmem->fdt_node;
>> +
>> +	if (of_get_flat_dt_prop(node, "reusable", NULL))
>> +		return -EINVAL;
>> +
>> +	rmem->ops = &rmem_dma_ops;
>> +	pr_info("Reserved memory: created DMA memory pool at %pa, size %ld MiB\n",
>> +		&rmem->base, (unsigned long)rmem->size / SZ_1M);
>> +	return 0;
>> +}
>> +RESERVEDMEM_OF_DECLARE(dma, "shared-dma-pool", rmem_dma_setup);
>> +#endif
>> -- 
>> 1.9.2

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland