[PATCH 2/2] powerpc/pseries: Check if EEH is enabled on DDW mechanism code

["Guilherme G. Piccoli" <gpiccoli@linux.vnet.ibm.com>]

The Dynamic DMA Window (DDW) mechanism relies on EEH to obtain the
configuration address of devices. For example, the functions query_ddw()
and create_ddw() make use of eeh_dev struct. So, the dependency is
intrinsic - DDW mechanism will fail if EEH is not enabled.

Despite this dependency, no check for EEH availability is performed in DDW
code. This patch adds a check based on eeh_enabled() function, so if EEH is
not enabled before eeh_dev struct use, DDW will fallback to default iommu
mechanism and won't fail.

One use case for this patch is when we disable EEH globally via kernel
command-line ("eeh=off") - without the patch, a device probe can hit a kernel
oops because EEH is disabled but DDW will try to use it.

Signed-off-by: Guilherme G. Piccoli <gpiccoli@linux.vnet.ibm.com>
---
 arch/powerpc/platforms/pseries/iommu.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/arch/powerpc/platforms/pseries/iommu.c b/arch/powerpc/platforms/pseries/iommu.c
index bd98ce2..1ff55cc 100644
--- a/arch/powerpc/platforms/pseries/iommu.c
+++ b/arch/powerpc/platforms/pseries/iommu.c
@@ -1224,8 +1224,10 @@ static int dma_set_mask_pSeriesLP(struct device *dev, u64 dma_mask)
 
 	pdev = to_pci_dev(dev);
 
-	/* only attempt to use a new window if 64-bit DMA is requested */
-	if (!disable_ddw && dma_mask == DMA_BIT_MASK(64)) {
+	/* We should check if EEH is enabled here, since DDW mechanism has
+	 * an intrinsic dependency of EEH config addr information. Also, we
+	 * only attempt to use a new window if 64-bit DMA is requested */
+	if (eeh_enabled() && !disable_ddw && dma_mask == DMA_BIT_MASK(64)) {
 		dn = pci_device_to_OF_node(pdev);
 		dev_dbg(dev, "node is %s\n", dn->full_name);
 
-- 
2.1.0