On Wed, 30 Apr 2014 10:19:15 -0400, Santosh Shilimkar [off-list ref] wrote:

Hi Grant,

On Tuesday 29 April 2014 10:41 AM, Grant Likely wrote:

quoted

On Thu, 24 Apr 2014 11:30:04 -0400, Santosh Shilimkar [off-list ref] wrote:

quoted

Retrieve DMA configuration from DT and setup platform device's DMA
parameters. The DMA configuration in DT has to be specified using
"dma-ranges" and "dma-coherent" properties if supported.

We setup dma_pfn_offset using "dma-ranges" and dma_coherent_ops
using "dma-coherent" device tree properties.

The set_arch_dma_coherent_ops macro has to be defined by arch if
it supports coherent dma_ops. Otherwise, set_arch_dma_coherent_ops() is
declared as nop.

Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Russell King <redacted>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Olof Johansson <redacted>
Cc: Grant Likely <redacted>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Linus Walleij <redacted>
Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
Signed-off-by: Santosh Shilimkar <redacted>
---
 drivers/of/platform.c       |   48 ++++++++++++++++++++++++++++++++++++++++---
 include/linux/dma-mapping.h |    7 +++++++
 2 files changed, 52 insertions(+), 3 deletions(-)

diff --git a/drivers/of/platform.c b/drivers/of/platform.c
index 48de98f..270c0b9 100644
--- a/drivers/of/platform.c
+++ b/drivers/of/platform.c

@@ -187,6 +187,50 @@ struct platform_device *of_device_alloc(struct device_node *np,
 EXPORT_SYMBOL(of_device_alloc);
 
 /**
+ * of_dma_configure - Setup DMA configuration
+ * @dev:	Device to apply DMA configuration
+ *
+ * Try to get devices's DMA configuration from DT and update it
+ * accordingly.
+ *
+ * In case if platform code need to use own special DMA configuration,it
+ * can use Platform bus notifier and handle BUS_NOTIFY_ADD_DEVICE event
+ * to fix up DMA configuration.
+ */
+static void of_dma_configure(struct device *dev)
+{
+	u64 dma_addr, paddr, size;
+	int ret;
+
+	dev->coherent_dma_mask = DMA_BIT_MASK(32);
+	if (!dev->dma_mask)
+		dev->dma_mask = &dev->coherent_dma_mask;
+
+	/*
+	 * if dma-coherent property exist, call arch hook to setup
+	 * dma coherent operations.
+	 */
+	if (of_dma_is_coherent(dev->of_node)) {
+		set_arch_dma_coherent_ops(dev);
+		dev_dbg(dev, "device is dma coherent\n");
+	}
+
+	/*
+	 * if dma-ranges property doesn't exist - just return else
+	 * setup the dma offset
+	 */
+	ret = of_dma_get_range(dev->of_node, &dma_addr, &paddr, &size);
+	if ((ret == -ENODEV) || (ret < 0)) {
+		dev_dbg(dev, "no dma range information to setup\n");
+		return;
+	}
+
+	/* DMA ranges found. Calculate and set dma_pfn_offset */
+	dev->dma_pfn_offset = PFN_DOWN(paddr - dma_addr);
+	dev_dbg(dev, "dma_pfn_offset(%#08lx)\n", dev->dma_pfn_offset);

I've got two concerns here. of_dma_get_range() retrieves only the first
tuple from the dma-ranges property, but it is perfectly valid for
dma-ranges to contain multiple tuples. How should we handle it if a
device has multiple ranges it can DMA from?

We've not found any cases in current Linux where more than one dma-ranges
would be used. Moreover, The MM (definitely for ARM) isn't supported such
cases at all (if i understand everything right).
- there are only one arm_dma_pfn_limit
- there is only one MM zone is used for ARM
- some arches like x86,mips can support 2 zones (per arch - not per device or bus)
  DMA & DMA32, but they configured once and forever per arch.

Okay. If anyone ever does implement multiple ranges then this code will
need to be revisited.

quoted

Second, while the pfn offset is being determined, I don't see anything
making use of either the base address or size. How is the device
constrained to only getting DMA buffers from within that range? Is the
driver expected to manage that directly?

Drivers don't have to do anything special apart from setting
the correct mask. The pfn_offset case, we use DMA_ZONE which takes
care of masks already. Size is suppose to be used for dma_mask
setup which we discussed in previous threads.

okay.

g.