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 <dbrownell@users.sourceforge.net>
Cc: David Miller <davem@davemloft.net>
Acked-by: Russell King <rmk@arm.linux.org.uk>
Cc: Andi Kleen <ak@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

Documentation/DMA-API.txt

@@ -68,6 +68,9 @@ size and dma_handle must all be the same as those passed into the
 consistent allocate.  cpu_addr must be the virtual address returned by
 the consistent allocate.
 
+Note that unlike their sibling allocation calls, these routines
+may only be called with IRQs enabled.
+
 
 Part Ib - Using small dma-coherent buffers
 ------------------------------------------

arch/x86/kernel/pci-dma_32.c

@@ -64,6 +64,7 @@ void dma_free_coherent(struct device *dev, size_t size,
 	struct dma_coherent_mem *mem = dev ? dev->dma_mem : NULL;
 	int order = get_order(size);
 
+	WARN_ON(irqs_disabled());	/* for portability */
 	if (mem && vaddr >= mem->virt_base && vaddr < (mem->virt_base + (mem->size << PAGE_SHIFT))) {
 		int page = (vaddr - mem->virt_base) >> PAGE_SHIFT;
 

arch/x86/kernel/pci-dma_64.c

@@ -167,6 +167,7 @@ EXPORT_SYMBOL(dma_alloc_coherent);
 void dma_free_coherent(struct device *dev, size_t size,
 			 void *vaddr, dma_addr_t bus)
 {
+	WARN_ON(irqs_disabled());	/* for portability */
 	if (dma_ops->unmap_single)
 		dma_ops->unmap_single(dev, bus, size, 0);
 	free_pages((unsigned long)vaddr, get_order(size));

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));