Re: [PATCH kernel v3 2/2] powerpc/dma: Fallback to dma_ops when persistent memory present

[Alexey Kardashevskiy]

On 29/10/2020 11:40, Michael Ellerman wrote:
Alexey Kardashevskiy <a...@ozlabs.ru> writes:
diff --git a/arch/powerpc/platforms/pseries/iommu.c 
b/arch/powerpc/platforms/pseries/iommu.c
index e4198700ed1a..91112e748491 100644
--- a/arch/powerpc/platforms/pseries/iommu.c
+++ b/arch/powerpc/platforms/pseries/iommu.c
@@ -1111,11 +1112,13 @@ static void reset_dma_window(struct pci_dev *dev, 
struct device_node *par_dn)
   */
  static u64 enable_ddw(struct pci_dev *dev, struct device_node *pdn)
  {
-       int len, ret;
+       int len = 0, ret;
+       bool pmem_present = of_find_node_by_type(NULL, "ibm,pmemory") != NULL;

That leaks a reference on the returned node.

        dn = of_find_node_by_type(NULL, "ibm,pmemory");
        pmem_present = dn != NULL;
        of_node_put(dn);


ah, true. v4 then.




@@ -1126,7 +1129,7 @@ static u64 enable_ddw(struct pci_dev *dev, struct 
device_node *pdn)
  
  	mutex_lock(&direct_window_init_mutex);
  
-	dma_addr = find_existing_ddw(pdn);
+       dma_addr = find_existing_ddw(pdn, &len);

I don't see len used anywhere?

        if (dma_addr != 0)
                goto out_unlock;
  
@@ -1212,14 +1215,26 @@ static u64 enable_ddw(struct pci_dev *dev, struct device_node *pdn)
        }
        /* verify the window * number of ptes will map the partition */
        /* check largest block * page size > max memory hotplug addr */
-       max_addr = ddw_memory_hotplug_max();
-       if (query.largest_available_block < (max_addr >> page_shift)) {
-               dev_dbg(&dev->dev, "can't map partition max 0x%llx with %llu "
-                         "%llu-sized pages\n", max_addr,  
query.largest_available_block,
-                         1ULL << page_shift);
+       /*
+        * The "ibm,pmemory" can appear anywhere in the address space.
+        * Assuming it is still backed by page structs, try MAX_PHYSMEM_BITS
+        * for the upper limit and fallback to max RAM otherwise but this
+        * disables device::dma_ops_bypass.
+        */
+       len = max_ram_len;

Here you override whatever find_existing_ddw() wrote to len?


Not always, there is a bunch of gotos before this line to the end of the 
function and one (which returns the existing window) is legit. Thanks,




+       if (pmem_present) {
+               if (query.largest_available_block >=
+                   (1ULL << (MAX_PHYSMEM_BITS - page_shift)))
+                       len = MAX_PHYSMEM_BITS - page_shift;
+               else
+                       dev_info(&dev->dev, "Skipping ibm,pmemory");
+       }
+
+       if (query.largest_available_block < (1ULL << (len - page_shift))) {
+               dev_dbg(&dev->dev, "can't map partition max 0x%llx with %llu 
%llu-sized pages\n",
+                       1ULL << len, query.largest_available_block, 1ULL << 
page_shift);
                goto out_failed;
        }
-       len = order_base_2(max_addr);
        win64 = kzalloc(sizeof(struct property), GFP_KERNEL);
        if (!win64) {
                dev_info(&dev->dev,


cheers


--
Alexey