On Fri, Feb 28, 2014 at 6:00 PM, Arnd Bergmann [off-list ref] wrote:

On Thursday 27 February 2014 16:17:50 Santosh Shilimkar wrote:

quoted

diff --git a/arch/arm/kernel/devtree.c b/arch/arm/kernel/devtree.c
index f751714..926b5dd 100644
--- a/arch/arm/kernel/devtree.c
+++ b/arch/arm/kernel/devtree.c

@@ -235,3 +238,61 @@ const struct machine_desc * __init setup_machine_fdt(unsigned int dt_phys)

      return mdesc;
 }
+
+void arm_dt_dma_configure(struct device *dev)
+{
+     dma_addr_t dma_addr;
+     phys_addr_t paddr, size;
+     dma_addr_t dma_mask;
+     int ret;
+
+     /*
+      * if dma-ranges property doesn't exist - use 32 bits DMA mask
+      * by default and don't set skip archdata.dma_pfn_offset
+      */
+     ret = of_dma_get_range(dev->of_node, &dma_addr, &paddr, &size);
+     if (ret == -ENODEV) {
+             dev->coherent_dma_mask = DMA_BIT_MASK(32);
+             if (!dev->dma_mask)
+                     dev->dma_mask = &dev->coherent_dma_mask;
+             return;
+     }

I think this is a reasonable default, but I also want Russell's
opinion on this, since I suspect he will argue that we shouldn't
default to setting a DMA mask for devices that are not DMA capable.

of_platform_device_create_pdata() in drivers/of/platform.c
does the same assumption since ages.

Maybe someone has an idea how we can detect all three important cases:

a) A device is marked as DMA capable using a dma-ranges property
b) A device is known not to be DMA capable
c) we don't have any dma-ranges properties in an old dtb file
   but still want 32 bit masks by default.

The exact same solution would apply to the of core right?

Yours,
Linus Walleij