problem with blk_queue_bounce_limit()

[David Mosberger]

On platforms with I/O MMU hardware, memory above 4GB, and IDE hard disks,
this check:

		BUG_ON(dma_addr < BLK_BOUNCE_ISA);

causes an instant panic.  The reason is quite obvious: since there is
an I/O MMU, BLK_BOUNCE_ISA is effectively unlimited, and most IDE
controllers can of course DMA only to <4GB.

So, the check is wrong.  I think the proper way to fix this is to pass
a "struct dev" into the routine and then to use dma_supported() to
check whether bounce buffers will be needed.  Do you agree?  If so,
can you fix it?

Thanks,

	--david