Re: [RESEND PATCH v2 2/4] PCI: Do not Use IORESOURCE_STARTALIGN to identify bridge resources

On 2016/6/21 9:50, Bjorn Helgaas wrote:

On Thu, Jun 02, 2016 at 01:46:49PM +0800, Yongji Xie wrote:

quoted

Now we use the IORESOURCE_STARTALIGN to identify bridge resources
in __assign_resources_sorted(). That's quite fragile. We can't
make sure that the PCI devices' resources will not use
IORESOURCE_STARTALIGN any more.

Can you explain this a little more?  I don't quite understand the
problem.  Maybe you can give an example of the problem?

Now there are two kinds of additional resources in the list: bridge
resource and SR-IOV resource. Here we just want to fix the
additional alignment for bridge. But if SR-IOV resource get the
flag IORESOURCE_STARTALIGN which is not only for bridge, the
current check seems to be wrong. And kernel parameter
"resource_alignment" could set IORESOURCE_STARTALIGN for
SR-IOV resource with my next patch applied.

Thanks,
Yongji

quoted

In this patch, we try to use a more robust way to identify
bridge resources.

Signed-off-by: Yongji Xie <redacted>
---
  drivers/pci/setup-bus.c |    9 ++++++---
  1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/drivers/pci/setup-bus.c b/drivers/pci/setup-bus.c
index 55641a3..216ddbc 100644
--- a/drivers/pci/setup-bus.c
+++ b/drivers/pci/setup-bus.c

@@ -390,6 +390,7 @@ static void __assign_resources_sorted(struct list_head *head,
  	struct pci_dev_resource *dev_res, *tmp_res, *dev_res2;
  	unsigned long fail_type;
  	resource_size_t add_align, align;
+	int index;
  
  	/* Check if optional add_size is there */
  	if (!realloc_head || list_empty(realloc_head))

@@ -410,11 +411,13 @@ static void __assign_resources_sorted(struct list_head *head,
  
  		/*
  		 * There are two kinds of additional resources in the list:
-		 * 1. bridge resource  -- IORESOURCE_STARTALIGN
-		 * 2. SR-IOV resource   -- IORESOURCE_SIZEALIGN
+		 * 1. bridge resource
+		 * 2. SR-IOV resource
  		 * Here just fix the additional alignment for bridge
  		 */
-		if (!(dev_res->res->flags & IORESOURCE_STARTALIGN))
+		index = dev_res->res - dev_res->dev->resource;
+		if (index < PCI_BRIDGE_RESOURCES ||
+			index > PCI_BRIDGE_RESOURCE_END)

I think the code looks OK; at least, it seems to match the comment.
I'd just like to understand the problem a little better.

quoted

  			continue;
  
  		add_align = get_res_add_align(realloc_head, dev_res->res);
-- 
1.7.9.5

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