Re: [PATCH 4/4] PCI: fix the io resource alignment calculation in pbus_size_io()

[Bjorn Helgaas <bhelgaas@google.com>]

On Tue, Aug 06, 2013 at 12:01:55PM -0600, Bjorn Helgaas wrote:
> On Tue, Aug 06, 2013 at 11:47:42PM +0800, Wei Yang wrote:
> > On Tue, Aug 06, 2013 at 07:44:21AM -0600, Bjorn Helgaas wrote:
> > >On Tue, Aug 06, 2013 at 02:19:24PM +0800, Wei Yang wrote:
> > >> On Mon, Aug 05, 2013 at 11:58:50AM -0600, Bjorn Helgaas wrote:
> > >> >[+cc Yinghai]
> > >> >
> > >> >On Fri, Aug 2, 2013 at 3:31 AM, Wei Yang <weiyang@linux.vnet.ibm.com> wrote:
> > >> >> In commit 462d9303 ("PCI: Align P2P windows using pcibios_window_alignment()"),
> > >> >> it introduce a new method to calculate the window alignment of P2P bridge.
> > >> >>
> > >> >> When the io_window_1k is set,  the calculation for the io resource alignment
> > >> >> is different from the original one. In the original logic before 462d9303,
> > >> >> the alignment is no bigger than 4K even the io_window_1k is set. The logic
> > >> >> introduced in 462d9303 will limit the alignment to 1k in this case.
> > >> >>
> > >> >> This patch fix this issue.
> > >> >
> > >> >Presumably this fixes a bug, but you don't say what it is.  "different
> > >> >from the original" is not a description of a problem.  You need
> > >> >something like "with the current code, we allocate the wrong window
> > >> >size in situation X, or we allocate a window with incorrect alignment
> > >> >in situation Y, etc."
> > >> >
> > >> 
> > >> With current code, we allocate the wrong window size when upstream bridge
> > >> could be 1k aligned and one of the downstream port is 4k aligned.
> > >> 
> > >> In this case, the "min_align" should be 4k. But the current code set
> > >> "min_align" to 1k.
> > >
> > 
> > Hmm... sorry I should say. 
> > 
> > With current code, we allocate the wrong window size and alignment when upstream 
> > bridge could be 1k aligned and one of the downstream port is 4k aligned.
> > 
> > In this case, the "min_align" should be 4k. But the current code set
> > "min_align" to 1k.
> 
> Actually, I think only the alignment is wrong (not the size).  But I do
> agree that this looks like a problem in the current code.  I'll write
> this up and post the patch soon.

Here's the patch I propose.  The code change is the same as I posted
yesterday; only the changelog is new.  I'll put these in next pending
comments.

Bjorn


commit 2d1d66780ecd12c9518835303f5302fc5262d49b
Author: Bjorn Helgaas <bhelgaas@google.com>
Date:   Mon Aug 5 16:15:10 2013 -0600

    PCI: Align bridge I/O windows as required by downstream devices & bridges
    
    An upstream bridge's I/O window must be at least as aligned as any
    downstream device or bridge requires.  In particular, if the upstream
    bridge supports 1K alignment but a downstream bridge requires 4K alignment,
    the upstream window must also be 4K aligned.
    
    Therefore, do not reduce the required alignment ("min_align") based on
    the upstream bridge's capabilities.
    
    Reported-by: Wei Yang <weiyang@linux.vnet.ibm.com>
    Suggested-by: Yinghai Lu <yinghai@kernel.org>
    Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>

diff --git a/drivers/pci/setup-bus.c b/drivers/pci/setup-bus.c
index d4f1ad9..8333c92 100644
--- a/drivers/pci/setup-bus.c
+++ b/drivers/pci/setup-bus.c
@@ -749,12 +749,12 @@ static void pbus_size_io(struct pci_bus *bus, resource_size_t min_size,
 	struct resource *b_res = find_free_bus_resource(bus, IORESOURCE_IO);
 	resource_size_t size = 0, size0 = 0, size1 = 0;
 	resource_size_t children_add_size = 0;
-	resource_size_t min_align, io_align, align;
+	resource_size_t min_align, align;
 
 	if (!b_res)
  		return;
 
-	io_align = min_align = window_alignment(bus, IORESOURCE_IO);
+	min_align = window_alignment(bus, IORESOURCE_IO);
 	list_for_each_entry(dev, &bus->devices, bus_list) {
 		int i;
 
@@ -781,9 +781,6 @@ static void pbus_size_io(struct pci_bus *bus, resource_size_t min_size,
 		}
 	}
 
-	if (min_align > io_align)
-		min_align = io_align;
-
 	size0 = calculate_iosize(size, min_size, size1,
 			resource_size(b_res), min_align);
 	if (children_add_size > add_size)