dma_free_coherent() needs irqs enabled (sigh)

On at least ARM (and I'm told MIPS too) dma_free_coherent() has a newish
call context requirement: unlike its dma_alloc_coherent() sibling, it may
not be called with IRQs disabled.  (This was new behavior on ARM as of late
2005, caused by ARM SMP updates.) This little surprise can be annoyingly
driver-visible.

Since it looks like that restriction won't be removed, this patch changes
the definition of the API to include that requirement.  Also, to help catch
nonportable drivers, it updates the x86 and swiotlb versions to include the
relevant warnings.  (I already observed that it trips on the
bus_reset_tasklet of the new firewire_ohci driver.)

Signed-off-by: David Brownell <[email protected]>
Cc: David Miller <[email protected]>
Acked-by: Russell King <[email protected]>
Cc: Andi Kleen <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>

lib/swiotlb.c

@@ -497,6 +497,7 @@ void
 swiotlb_free_coherent(struct device *hwdev, size_t size, void *vaddr,
 		      dma_addr_t dma_handle)
 {
+	WARN_ON(irqs_disabled());
 	if (!(vaddr >= (void *)io_tlb_start
                     && vaddr < (void *)io_tlb_end))
 		free_pages((unsigned long) vaddr, get_order(size));