Re: [PATCH v7 3/8] arm64: introduce is_device_dma_coherent

From: Catalin Marinas
Date: Wed Nov 05 2014 - 11:57:04 EST

On Mon, Nov 03, 2014 at 11:10:18AM +0000, Stefano Stabellini wrote:
> On Mon, 3 Nov 2014, Will Deacon wrote:
> > On Mon, Nov 03, 2014 at 10:46:03AM +0000, Stefano Stabellini wrote:
> > > On Mon, 27 Oct 2014, Stefano Stabellini wrote:
> > > > Introduce a boolean flag and an accessor function to check whether a
> > > > device is dma_coherent. Set the flag from set_arch_dma_coherent_ops.
> > > >
> > > > Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
> > > > Signed-off-by: Catalin Marinas <catalin.marinas@xxxxxxx>
> > > > CC: will.deacon@xxxxxxx
> > >
> > > Will, Catalin,
> > > are you OK with this patch?
> >
> > It would be nicer if the dma_coherent flag didn't have to be duplicated by
> > each architecture in dev_archdata. Is there any reason not to put it in the
> > core code?
>
> Yes, there is a reason for it: if I added a boolean dma_coherent flag in
> struct device as Catalin initially suggested, what would be the default
> for each architecture? Where would I set it for arch that don't use
> device tree?

You don't need to. An architecture that has coherent DMA always doesn't
need to do anything. One that has non-coherent DMA always only needs to
select HAVE_DMA_NONCOHERENT. One that has a mix of both needs to find a
way to set dev->dma_coherent. Since that's a new API you introduce, it
doesn't break any existing architectures.

Note that if !is_device_dma_coherent(), it doesn't always mean that
standard cache maintenance would be enough (but that's a Xen problem,
not sure how to solve).


diff --git a/arch/Kconfig b/arch/Kconfig
index 05d7a8a458d5..8462b2e7491b 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -203,6 +203,9 @@ config HAVE_DMA_ATTRS
config HAVE_DMA_CONTIGUOUS
bool

+config HAVE_DMA_NONCOHERENT
+ bool
+
config GENERIC_SMP_IDLE_THREAD
bool

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 89c4b5ccc68d..fd7d5522764c 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -40,6 +40,7 @@ config ARM
select HAVE_DMA_API_DEBUG
select HAVE_DMA_ATTRS
select HAVE_DMA_CONTIGUOUS if MMU
+ select HAVE_DMA_NONCOHERENT if OF
select HAVE_DYNAMIC_FTRACE if (!XIP_KERNEL)
select HAVE_EFFICIENT_UNALIGNED_ACCESS if (CPU_V6 || CPU_V6K || CPU_V7) && MMU
select HAVE_FTRACE_MCOUNT_RECORD if (!XIP_KERNEL)
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 9532f8d5857e..eb7a5aa64e0e 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -46,6 +46,7 @@ config ARM64
select HAVE_DMA_API_DEBUG
select HAVE_DMA_ATTRS
select HAVE_DMA_CONTIGUOUS
+ select HAVE_DMA_NONCOHERENT
select HAVE_DYNAMIC_FTRACE
select HAVE_EFFICIENT_UNALIGNED_ACCESS
select HAVE_FTRACE_MCOUNT_RECORD
diff --git a/drivers/of/platform.c b/drivers/of/platform.c
index 3b64d0bf5bba..7e827726b702 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 = true;
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..0bdffba2337d 100644
--- a/include/linux/dma-mapping.h
+++ b/include/linux/dma-mapping.h
@@ -78,6 +78,18 @@ static inline int is_device_dma_capable(struct device *dev)
return dev->dma_mask != NULL && *dev->dma_mask != DMA_MASK_NONE;
}

+#ifdef CONFIG_HAVE_DMA_NONCOHERENT
+static inline int is_device_dma_coherent(struct device *dev)
+{
+ return dev->dma_coherent;
+}
+#else
+static inline int is_device_dma_coherent(struct device *dev)
+{
+ return 1
+}
+#endif
+
#ifdef CONFIG_HAS_DMA
#include <asm/dma-mapping.h>
#else
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 9532f8d5857e..eb7a5aa64e0e 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -46,6 +46,7 @@ config ARM64
select HAVE_DMA_API_DEBUG
select HAVE_DMA_ATTRS
select HAVE_DMA_CONTIGUOUS
+ select HAVE_DMA_NONCOHERENT
select HAVE_DYNAMIC_FTRACE
select HAVE_EFFICIENT_UNALIGNED_ACCESS
select HAVE_FTRACE_MCOUNT_RECORD
diff --git a/drivers/of/platform.c b/drivers/of/platform.c
index 3b64d0bf5bba..7e827726b702 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 = true;
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..0bdffba2337d 100644
--- a/include/linux/dma-mapping.h
+++ b/include/linux/dma-mapping.h
@@ -78,6 +78,18 @@ static inline int is_device_dma_capable(struct device *dev)
return dev->dma_mask != NULL && *dev->dma_mask != DMA_MASK_NONE;
}

+#ifdef CONFIG_HAVE_DMA_NONCOHERENT
+static inline int is_device_dma_coherent(struct device *dev)
+{
+ return dev->dma_coherent;
+}
+#else
+static inline int is_device_dma_coherent(struct device *dev)
+{
+ return 1
+}
+#endif
+
#ifdef CONFIG_HAS_DMA
#include <asm/dma-mapping.h>
#else
--
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