Hi all,
I have a memory area which is written by the CPU and concurrently read
by a DMA capable device, multiple times.
Among else there are two fields in the memory area, both are 32 bits
wide. Whenever the CPU updates the fields, I have to make sure that the
device does not get to see a new value in field B before I updated field
A. Conversely, it is safe to update field A anytime before field B. The
driver has no way to know when the device is going to read any of the
fields.
My question: Do I need wmb() within the following code?
dma_sync_single_for_cpu(..., DMA_TO_DEVICE);
area->a = new_val_a;
wmb(); /* necessary? */
area->b = new_val_b;
dma_sync_single_for_device(..., DMA_TO_DEVICE);
Or are all changes to the area hidden from the device between
dma_sync_single_for_cpu and _for_device, thereby making the write order
a non-issue? Thanks,
--
Stefan Richter
-=====-=-==- -=== -=--=
http://arcgraph.de/sr/
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