There are some devices that only allow 1 DMA window to exist at a time, and in those cases, a DDW is never created to them, since the default DMA window keeps using this resource.
LoPAR recommends this procedure: 1. Remove the default DMA window, 2. Query for which configs the DDW can be created, 3. Create a DDW. Patch #1: Create defines for outputs of ibm,ddw-applicable, so it's easier to identify them. Patch #2: - After LoPAR level 2.8, there is an extension that can make ibm,query-pe-dma-windows to have 6 outputs instead of 5. This changes the order of the outputs, and that can cause some trouble. - query_ddw() was updated to check how many outputs the ibm,query-pe-dma-windows is supposed to have, update the rtas_call() and deal correctly with the outputs in both cases. - This patch looks somehow unrelated to the series, but it can avoid future problems on DDW creation. Patch #3 moves the window-removing code from remove_ddw() to remove_dma_window(), creating a way to delete any DMA window, so it can be used to delete the default DMA window. Patch #4 makes use of the remove_dma_window() from patch #3 to remove the default DMA window before query_ddw(). It also implements a new rtas call to recover the default DMA window, in case anything fails after it was removed, and a DDW couldn't be created. Patch #5: Instead of destroying the created DDW if it doesn't map the whole partition, make use of it instead of the default DMA window. Patch #6: Changes the way iommu_bypass_supported_pSeriesLP() check for iommu_bypass: instead of checking the address returned by enable_ddw(), it checks a new output value that reflects if the DDW created maps the whole partition. All patches were tested into an LPAR with an Ethernet VF: 4005:01:00.0 Ethernet controller: Mellanox Technologies MT27700 Family [ConnectX-4 Virtual Function] --- Changes since v1: - Add defines for ibm,ddw-applicable and ibm,ddw-extensions outputs - Merge aux function query_ddw_out_sz() into query_ddw() - Merge reset_dma_window() patch (prev. #2) into remove default DMA window patch (#4). - Keep device_node *np name instead of using pdn in remove_*() - Rename 'device_node *pdn' into 'parent' in new functions - Rename dfl_win to default_win - Only remove the default DMA window if there is no window available in first query. - Check if default DMA window can be restored before removing it. - Fix 'unitialized use' (found by travis mpe:ci-test) - New patches #5 and #6 Special thanks for Alexey Kardashevskiy and Oliver O'Halloran for the feedback provided! Leonardo Bras (6): powerpc/pseries/iommu: Create defines for operations in ibm,ddw-applicable powerpc/pseries/iommu: Update call to ibm,query-pe-dma-windows powerpc/pseries/iommu: Move window-removing part of remove_ddw into remove_dma_window powerpc/pseries/iommu: Remove default DMA window before creating DDW powerpc/pseries/iommu: Make use of DDW even if it does not map the partition powerpc/pseries/iommu: Avoid errors when DDW starts at 0x00 arch/powerpc/platforms/pseries/iommu.c | 239 ++++++++++++++++++------- 1 file changed, 176 insertions(+), 63 deletions(-) -- 2.25.4