powerpc/pseries/iommu: remove default window before attempting DDW manipulation
An upcoming release of firmware will add DDW extensions, in particular an API to "reset" the DMA window to the original configuration (32-bit, 2GB in size). With that API available, we can safely remove the default window, increasing the resources available to firmware for creation of larger windows for the slot in question -- if we encounter an error, we can use the new API to reset the state of the slot. Further, this same release of firmware will make it a hard requirement for OSes to release the existing window before any other windows will be shown as available, to avoid conflicts in addressing between the two windows. In anticipation of these changes, always remove the default window before we do any DDW manipulations. Signed-off-by: Nishanth Aravamudan <nacc@us.ibm.com> Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
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