[RFC PATCH v6 3/7] drivers: dma-coherent: Account dma_pfn_offset when used with device tree

[Vladimir Murzin]

dma_declare_coherent_memory() and friends are designed to account
difference in CPU and device addresses. However, when it is used with
reserved memory regions there is assumption that CPU and device have
the same view on address space. This assumption gets invalid when
reserved memory for coherent DMA allocations is referenced by device
with non-empty "dma-range" property.

Simply feeding device address as rmem->base + dev->dma_pfn_offset
would not work due to reserved memory region can be shared, so this
patch turns device address to be expressed with help of CPU address
and device's dma_pfn_offset.

For the case where device tree is not used and device sees memory
different to CPU we explicitly set device's dma_pfn_offset to
accomplish such difference. The latter might look controversial, but
it seems only a few drivers set device address different to CPU's:
- drivers/usb/host/ohci-sm501.c
- arch/sh/drivers/pci/fixups-dreamcast.c
so they can be screwed only if dma_pfn_offset there is set and not in
sync with device address range - we try to catch such cases with
WARN_ON.

Cc: Michal Nazarewicz <mina86 at mina86.com>
Cc: Marek Szyprowski <m.szyprowski at samsung.com>
Cc: Alan Stern <stern at rowland.harvard.edu>
Cc: Yoshinori Sato <ysato at users.sourceforge.jp>
Cc: Rich Felker <dalias at libc.org>
Cc: Roger Quadros <rogerq at ti.com>
Cc: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
Tested-by: Benjamin Gaignard <benjamin.gaignard at linaro.org>
Tested-by: Andras Szemzo <sza at esh.hu>
Signed-off-by: Vladimir Murzin <vladimir.murzin at arm.com>
---
 drivers/base/dma-coherent.c | 17 +++++++++++++++--
 1 file changed, 15 insertions(+), 2 deletions(-)

diff --git a/drivers/base/dma-coherent.c b/drivers/base/dma-coherent.c
index 640a7e6..c59708c 100644
--- a/drivers/base/dma-coherent.c
+++ b/drivers/base/dma-coherent.c
@@ -18,6 +18,12 @@ struct dma_coherent_mem {
 	spinlock_t	spinlock;
 };
 
+static inline dma_addr_t dma_get_device_base(struct device *dev,
+					     struct dma_coherent_mem * mem)
+{
+	return (mem->pfn_base - dev->dma_pfn_offset) << PAGE_SHIFT;
+}
+
 static bool dma_init_coherent_memory(
 	phys_addr_t phys_addr, dma_addr_t device_addr, size_t size, int flags,
 	struct dma_coherent_mem **mem)
@@ -83,9 +89,16 @@ static void dma_release_coherent_memory(struct dma_coherent_mem *mem)
 static int dma_assign_coherent_memory(struct device *dev,
 				      struct dma_coherent_mem *mem)
 {
+	unsigned long dma_pfn_offset = mem->pfn_base - PFN_DOWN(mem->device_base);
+
 	if (dev->dma_mem)
 		return -EBUSY;
 
+	if (dev->dma_pfn_offset)
+		WARN_ON(dma_pfn_offset && (dev->dma_pfn_offset != dma_pfn_offset));
+	else
+		dev->dma_pfn_offset = dma_pfn_offset;
+
 	dev->dma_mem = mem;
 	/* FIXME: this routine just ignores DMA_MEMORY_INCLUDES_CHILDREN */
 
@@ -133,7 +146,7 @@ void *dma_mark_declared_memory_occupied(struct device *dev,
 		return ERR_PTR(-EINVAL);
 
 	spin_lock_irqsave(&mem->spinlock, flags);
-	pos = (device_addr - mem->device_base) >> PAGE_SHIFT;
+	pos = PFN_DOWN(device_addr - dma_get_device_base(dev, mem));
 	err = bitmap_allocate_region(mem->bitmap, pos, get_order(size));
 	spin_unlock_irqrestore(&mem->spinlock, flags);
 
@@ -186,7 +199,7 @@ int dma_alloc_from_coherent(struct device *dev, ssize_t size,
 	/*
 	 * Memory was found in the per-device area.
 	 */
-	*dma_handle = mem->device_base + (pageno << PAGE_SHIFT);
+	*dma_handle = dma_get_device_base(dev, mem) + (pageno << PAGE_SHIFT);
 	*ret = mem->virt_base + (pageno << PAGE_SHIFT);
 	dma_memory_map = (mem->flags & DMA_MEMORY_MAP);
 	spin_unlock_irqrestore(&mem->spinlock, flags);
-- 
2.0.0