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Message-ID: <20150610162819.GD22844@e104818-lin.cambridge.arm.com>
Date: Wed, 10 Jun 2015 17:28:19 +0100
From: Catalin Marinas <catalin.marinas@....com>
To: Lorenzo Nava <lorenx4@...il.com>
Cc: arnd@...db.de, linux@....linux.org.uk,
linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [RFC PATCH v2] arm DMA: Fix allocation from CMA for coherent DMA
On Wed, Jun 03, 2015 at 07:15:45PM +0200, Lorenzo Nava wrote:
> This patch allows the use of CMA for DMA coherent memory allocation.
> At the moment if the input parameter "is_coherent" is set to true
> the allocation is not made using the CMA, which I think is not the
> desired behaviour.
>
> Signed-off-by: Lorenzo Nava <lorenx4@...xxxxx>
> ---
> Changes in v2:
> correct __arm_dma_free() according to __dma_alloc() allocation
> ---
> arch/arm/mm/dma-mapping.c | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/arch/arm/mm/dma-mapping.c b/arch/arm/mm/dma-mapping.c
> index 7e7583d..15643b9 100644
> --- a/arch/arm/mm/dma-mapping.c
> +++ b/arch/arm/mm/dma-mapping.c
> @@ -645,9 +645,9 @@ static void *__dma_alloc(struct device *dev, size_t size, dma_addr_t *handle,
> size = PAGE_ALIGN(size);
> want_vaddr = !dma_get_attr(DMA_ATTR_NO_KERNEL_MAPPING, attrs);
>
> - if (is_coherent || nommu())
> + if (nommu())
> addr = __alloc_simple_buffer(dev, size, gfp, &page);
> - else if (!(gfp & __GFP_WAIT))
> + else if (!is_coherent && !(gfp & __GFP_WAIT))
> addr = __alloc_from_pool(size, &page);
> else if (!dev_get_cma_area(dev))
> addr = __alloc_remap_buffer(dev, size, gfp, prot, &page, caller, want_vaddr);
So while you allow __alloc_from_contiguous() to be called when
is_coherent, the memory returned is still non-cacheable. The reason is
that the "prot" argument passed to __dma_alloc() in
arm_coherent_dma_alloc() is pgprot_dmacoherent(PAGE_KERNEL) which means
Normal NonCacheable memory. The mmap seems to create a cacheable mapping
as vma->vm_page_prot is not passed through __get_dma_pgprot().
I think you need something like below, completely untested:
diff --git a/arch/arm/mm/dma-mapping.c b/arch/arm/mm/dma-mapping.c
index 1ced8a0f7a52..1ee3d8e8c313 100644
--- a/arch/arm/mm/dma-mapping.c
+++ b/arch/arm/mm/dma-mapping.c
@@ -573,11 +573,13 @@ static void __free_from_contiguous(struct device *dev, struct page *page,
dma_release_from_contiguous(dev, page, size >> PAGE_SHIFT);
}
-static inline pgprot_t __get_dma_pgprot(struct dma_attrs *attrs, pgprot_t prot)
+static inline pgprot_t __get_dma_pgprot(struct dma_attrs *attrs, pgprot_t prot,
+ bool coherent)
{
- prot = dma_get_attr(DMA_ATTR_WRITE_COMBINE, attrs) ?
- pgprot_writecombine(prot) :
- pgprot_dmacoherent(prot);
+ if (dma_get_attr(DMA_ATTR_WRITE_COMBINE))
+ prot = pgprot_writecombine(prot);
+ else if (!coherent)
+ prot = pgprot_dmacoherent(prot);
return prot;
}
@@ -587,7 +589,7 @@ static inline pgprot_t __get_dma_pgprot(struct dma_attrs *attrs, pgprot_t prot)
#define nommu() 1
-#define __get_dma_pgprot(attrs, prot) __pgprot(0)
+#define __get_dma_pgprot(attrs, prot, coherent) __pgprot(0)
#define __alloc_remap_buffer(dev, size, gfp, prot, ret, c, wv) NULL
#define __alloc_from_pool(size, ret_page) NULL
#define __alloc_from_contiguous(dev, size, prot, ret, c, wv) NULL
@@ -670,7 +672,7 @@ static void *__dma_alloc(struct device *dev, size_t size, dma_addr_t *handle,
void *arm_dma_alloc(struct device *dev, size_t size, dma_addr_t *handle,
gfp_t gfp, struct dma_attrs *attrs)
{
- pgprot_t prot = __get_dma_pgprot(attrs, PAGE_KERNEL);
+ pgprot_t prot = __get_dma_pgprot(attrs, PAGE_KERNEL, false);
void *memory;
if (dma_alloc_from_coherent(dev, size, handle, &memory))
@@ -683,7 +685,7 @@ void *arm_dma_alloc(struct device *dev, size_t size, dma_addr_t *handle,
static void *arm_coherent_dma_alloc(struct device *dev, size_t size,
dma_addr_t *handle, gfp_t gfp, struct dma_attrs *attrs)
{
- pgprot_t prot = __get_dma_pgprot(attrs, PAGE_KERNEL);
+ pgprot_t prot = __get_dma_pgprot(attrs, PAGE_KERNEL, true);
void *memory;
if (dma_alloc_from_coherent(dev, size, handle, &memory))
@@ -733,7 +735,7 @@ int arm_dma_mmap(struct device *dev, struct vm_area_struct *vma,
struct dma_attrs *attrs)
{
#ifdef CONFIG_MMU
- vma->vm_page_prot = __get_dma_pgprot(attrs, vma->vm_page_prot);
+ vma->vm_page_prot = __get_dma_pgprot(attrs, vma->vm_page_prot, false);
#endif /* CONFIG_MMU */
return __arm_dma_mmap(dev, vma, cpu_addr, dma_addr, size, attrs);
}
@@ -1362,7 +1364,7 @@ static void __iommu_free_atomic(struct device *dev, void *cpu_addr,
static void *arm_iommu_alloc_attrs(struct device *dev, size_t size,
dma_addr_t *handle, gfp_t gfp, struct dma_attrs *attrs)
{
- pgprot_t prot = __get_dma_pgprot(attrs, PAGE_KERNEL);
+ pgprot_t prot = __get_dma_pgprot(attrs, PAGE_KERNEL, is_device_dma_coherent(dev));
struct page **pages;
void *addr = NULL;
@@ -1414,7 +1416,7 @@ static int arm_iommu_mmap_attrs(struct device *dev, struct vm_area_struct *vma,
unsigned long usize = vma->vm_end - vma->vm_start;
struct page **pages = __iommu_get_pages(cpu_addr, attrs);
- vma->vm_page_prot = __get_dma_pgprot(attrs, vma->vm_page_prot);
+ vma->vm_page_prot = __get_dma_pgprot(attrs, vma->vm_page_prot, is_device_dma_coherent(dev));
if (!pages)
return -ENXIO;
--
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