Alexander Popov wrote:

The only question I have: why calling dma_unmap_single() from within
a spinlock is a bad practice?

I don't know, but usually functions that allocate or free memory cannot 
be called from within a spinlock.  You need to check that.  Since the 
MPC5121 is a single-core CPU, you might not notice if you're doing 
something wrong.
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