powerpc/pseries/iommu: enable_ddw incorrectly returns direct mapping for SR-IOV device

When a device is initialized, the driver invokes dma_supported() twice -
first for streaming mappings followed by coherent mappings. For an
SR-IOV device, default window is deleted and DDW created. With vPMEM
enabled, TCE mappings are dynamically created for both vPMEM and SR-IOV
device. There are no direct mappings.

First time when dma_supported() is called with 64 bit mask, DDW is created
and marked as dynamic window. The second time dma_supported() is called,
enable_ddw() finds existing window for the device and incorrectly returns
it as "direct mapping".

This only happens when size of DDW is big enough to map max LPAR memory.

This results in streaming TCEs to not get dynamically mapped, since code
incorrently assumes these are already pre-mapped. The adapter initially
comes up but goes down due to EEH.

Fixes: 381ceda88c4c ("powerpc/pseries/iommu: Make use of DDW for indirect mapping")
Cc: [e-mail] # v5.15+
Signed-off-by: Gaurav Batra <[e-mail]>
Signed-off-by: Michael Ellerman <[e-mail]>
Link: https://msgid.link/[e-mail]

arch/powerpc/platforms/pseries/iommu.c

···
 	return 0;
 }
 
-static bool find_existing_ddw(struct device_node *pdn, u64 *dma_addr, int *window_shift)
+static bool find_existing_ddw(struct device_node *pdn, u64 *dma_addr, int *window_shift,
+			      bool *direct_mapping)
 {
 	struct dma_win *window;
 	const struct dynamic_dma_window_prop *dma64;
···
 			dma64 = window->prop;
 			*dma_addr = be64_to_cpu(dma64->dma_base);
 			*window_shift = be32_to_cpu(dma64->window_shift);
+			*direct_mapping = window->direct;
 			found = true;
 			break;
 		}
···
 
 	mutex_lock(&dma_win_init_mutex);
 
-	if (find_existing_ddw(pdn, &dev->dev.archdata.dma_offset, &len)) {
-		direct_mapping = (len >= max_ram_len);
+	if (find_existing_ddw(pdn, &dev->dev.archdata.dma_offset, &len, &direct_mapping))
 		goto out_unlock;
-	}
 
 	/*
 	 * If we already went through this for a previous function of