of: Add OF_DMA_DEFAULT_COHERENT & select it on powerpc

commit dabf6b36b83a18d57e3d4b9d50544ed040d86255 upstream.

There's an OF helper called of_dma_is_coherent(), which checks if a
device has a "dma-coherent" property to see if the device is coherent
for DMA.

But on some platforms devices are coherent by default, and on some
platforms it's not possible to update existing device trees to add the
"dma-coherent" property.

So add a Kconfig symbol to allow arch code to tell
of_dma_is_coherent() that devices are coherent by default, regardless
of the presence of the property.

Select that symbol on powerpc when NOT_COHERENT_CACHE is not set, ie.
when the system has a coherent cache.

Fixes: 92ea637edea3 ("of: introduce of_dma_is_coherent() helper")
Cc: stable@vger.kernel.org # v3.16+
Reported-by: Christian Zigotzky <chzigotzky@xenosoft.de>
Tested-by: Christian Zigotzky <chzigotzky@xenosoft.de>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Reviewed-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Rob Herring <robh@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 01b6c00..4ece201 100644 (file)
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -93,6 +93,7 @@ config PPC
        select BINFMT_ELF
        select ARCH_HAS_ELF_RANDOMIZE
        select OF
+       select OF_DMA_DEFAULT_COHERENT          if !NOT_COHERENT_CACHE
        select OF_EARLY_FLATTREE
        select OF_RESERVED_MEM
        select HAVE_FTRACE_MCOUNT_RECORD

diff --git a/drivers/of/Kconfig b/drivers/of/Kconfig
index e2a4841..4ba54ff 100644 (file)
--- a/drivers/of/Kconfig
+++ b/drivers/of/Kconfig
@@ -112,4 +112,8 @@ config OF_OVERLAY
          While this option is selected automatically when needed, you can
          enable it manually to improve device tree unit test coverage.
 
+config OF_DMA_DEFAULT_COHERENT
+       # arches should select this if DMA is coherent by default for OF devices
+       bool
+
 endif # OF

diff --git a/drivers/of/address.c b/drivers/of/address.c
index 4fe5fe2..b3bf876 100644 (file)
--- a/drivers/of/address.c
+++ b/drivers/of/address.c
@@ -1009,12 +1009,16 @@ EXPORT_SYMBOL_GPL(of_dma_get_range);
  * @np:        device node
  *
  * It returns true if "dma-coherent" property was found
- * for this device in DT.
+ * for this device in the DT, or if DMA is coherent by
+ * default for OF devices on the current platform.
  */
 bool of_dma_is_coherent(struct device_node *np)
 {
        struct device_node *node = of_node_get(np);
 
+       if (IS_ENABLED(CONFIG_OF_DMA_DEFAULT_COHERENT))
+               return true;
+
        while (node) {
                if (of_property_read_bool(node, "dma-coherent")) {
                        of_node_put(node);