>> How could be spl() implemented to avoid the need for volatiles?
> It needs to have a memory clobber + __insn_barrier().

How would that avoid the ned for volatile marking on stuff shared
between driver top half and driver bottom half?  You still need
volatile to prevent the compiler from generating code assuming that,
for example, successive reads without stores in between will return the
same value, or that stores can be deferred without harm.

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