[PATCH v2 1/2] drivers: dma-coherent: Fix dev->cma_area vs dev->dma_mem breakage

From: Vitaly Kuzmichev
Date: Fri Jul 07 2017 - 09:23:17 EST

From: "George G. Davis" <george_davis@xxxxxxxxxx>

When a "linux,dma-default" DMA coherent region is defined, the
dma_coherent_default_memory pointer is returned by function
dev_get_coherent_memory() for any struct device *dev which has not
explicitly assigned a dev->dma_mem memory region, i.e. dev->dma_mem is
the NULL pointer. Unfortunately this overlooks the fact that for the
CONFIG_DMA_CMA case, it is also possible that a device may have assigned
a CMA memory region via the dev->cma_area pointer in which case,
the "linux,dma-default" DMA coherent region should not be used.
Since the current code did not consider this case, dev->cma_area regions
are not used when a "linux,dma-default" DMA coherent region is defined.
Instead, memory is allocated from the "linux,dma-default" DMA coherent
region. This omission could lead to DMA memory allocation failures for
devices such as the "viv,galcore" which require a large contiguous
address space which cannot be supplied by the "linux,dma-default" region
IFF it has been reconfigured to use a CMA memory region. Similar DMA
allocation failures are likely to occur for other devices which require
large memory regions and/or overall allocation requests exceed the size
of the "linux,dma-default" DMA coherent region size.

Fix this by updating the dev_get_coherent_memory() function to return
the NULL pointer if a dev->cma_area region is assigned to a device.

Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxx>
Cc: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>
Cc: Robin Murphy <robin.murphy@xxxxxxx>
Signed-off-by: George G. Davis <george_davis@xxxxxxxxxx>
Signed-off-by: Vitaly Kuzmichev <vitaly_kuzmichev@xxxxxxxxxx>
drivers/base/dma-coherent.c | 4 ++++
1 file changed, 4 insertions(+)

diff --git a/drivers/base/dma-coherent.c b/drivers/base/dma-coherent.c
index 2ae24c2..acfe140 100644
--- a/drivers/base/dma-coherent.c
+++ b/drivers/base/dma-coherent.c
@@ -25,6 +25,10 @@ static inline struct dma_coherent_mem *dev_get_coherent_memory(struct device *de
if (dev && dev->dma_mem)
return dev->dma_mem;
+ if (dev && dev->cma_area)
+ return NULL;
return dma_coherent_default_memory;