Re: [PATCH v4 3/7] [RFC] arm/arm64: introduce is_dma_coherent

From: Catalin Marinas
Date: Fri Oct 24 2014 - 11:44:17 EST


On Fri, Oct 24, 2014 at 12:39:59PM +0100, Stefano Stabellini wrote:
> On Fri, 24 Oct 2014, Catalin Marinas wrote:
> > I think a better way would be some Xen hook around
> > set_arch_dma_coherent_ops(). Does Xen have its own device tracking
> > structures? If not, you may be able to add another bitfield to the
> > kernel one.
>
> We don't have an additional device tracking struct on Xen.
> I agree that a new bit somewhere would be the best solution, but I am
> not sure where. Maybe in dev_archdata under arm and arm64? After all it
> is already used to keep pointers to dma and coherency related
> structures.

I was thinking about something like below (maybe with some additional
ARCH_HAS_NONCOHERENT_DMA config for architectures that are always
coherent):

diff --git a/drivers/of/platform.c b/drivers/of/platform.c
index 3b64d0bf5bba..ae399ccbd569 100644
--- a/drivers/of/platform.c
+++ b/drivers/of/platform.c
@@ -183,6 +183,7 @@ static void of_dma_configure(struct device *dev)
* dma coherent operations.
*/
if (of_dma_is_coherent(dev->of_node)) {
+ dev->dma_coherent = 1;
set_arch_dma_coherent_ops(dev);
dev_dbg(dev, "device is dma coherent\n");
}
diff --git a/include/linux/device.h b/include/linux/device.h
index ce1f21608b16..e00ca876db01 100644
--- a/include/linux/device.h
+++ b/include/linux/device.h
@@ -796,6 +796,7 @@ struct device {

bool offline_disabled:1;
bool offline:1;
+ bool dma_coherent:1;
};

static inline struct device *kobj_to_dev(struct kobject *kobj)
diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
index d5d388160f42..9c9ba5a5428e 100644
--- a/include/linux/dma-mapping.h
+++ b/include/linux/dma-mapping.h
@@ -78,6 +78,11 @@ static inline int is_device_dma_capable(struct device *dev)
return dev->dma_mask != NULL && *dev->dma_mask != DMA_MASK_NONE;
}

+static inline int is_device_dma_coherent(struct device *dev)
+{
+ return dev->dma_coherent;
+}
+
#ifdef CONFIG_HAS_DMA
#include <asm/dma-mapping.h>
#else

> However given the timing constraints I hope you would be OK with the
> suboptimal solution for now and create a common is_dma_coherent function
> in 3.19?

If you want to push something for 3.18, you could have a temporary
solution but I would prefer a bool or something in the dev_archdata
structure. Another untested patch:

diff --git a/arch/arm64/include/asm/device.h b/arch/arm64/include/asm/device.h
index cf98b362094b..243ef256b8c9 100644
--- a/arch/arm64/include/asm/device.h
+++ b/arch/arm64/include/asm/device.h
@@ -21,6 +21,7 @@ struct dev_archdata {
#ifdef CONFIG_IOMMU_API
void *iommu; /* private IOMMU data */
#endif
+ bool dma_coherent;
};

struct pdev_archdata {
diff --git a/arch/arm64/include/asm/dma-mapping.h b/arch/arm64/include/asm/dma-mapping.h
index adeae3f6f0fc..b6bc4c268878 100644
--- a/arch/arm64/include/asm/dma-mapping.h
+++ b/arch/arm64/include/asm/dma-mapping.h
@@ -54,11 +54,17 @@ static inline void set_dma_ops(struct device *dev, struct dma_map_ops *ops)

static inline int set_arch_dma_coherent_ops(struct device *dev)
{
+ dev->dev_archdata.dma_coherent = true;
set_dma_ops(dev, &coherent_swiotlb_dma_ops);
return 0;
}
#define set_arch_dma_coherent_ops set_arch_dma_coherent_ops

+static inline int is_device_dma_coherent(struct device *dev)
+{
+ return dev->dev_archdata.dma_coherent;
+}
+
#include <asm-generic/dma-mapping-common.h>

static inline dma_addr_t phys_to_dma(struct device *dev, phys_addr_t paddr)


This way you don't have to test for swiotlb vs iommu ops (we don't have
the latter yet on arm64 but they are coming).

--
Catalin
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