From: Alexey Neyman <stilor@att.net>
To: Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>,
        "H. Peter Anvin" <hpa@zytor.com>, Bjorn Helgaas <bhelgaas@google.com>,
        "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>,
        Feng Tang <feng.tang@intel.com>, Yijing Wang <wangyijing@huawei.com>
Cc: x86@kernel.org, linux-kernel@vger.kernel.org
Subject: [PATCH] Fix coalescing host bridge windows in arch/x86/pci/acpi.c
Date: Sun, 22 Sep 2013 23:15:46 -0700
Message-ID: <6362938.J7ZtNEOFpc@mistral>
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[Resending due to no response to the original message in a week]

Hi all,

I have a board with a BIOS bug that reports the following I/O port regions in 
_CRS on one of the host bridges:

0x0000-0x03af // #0
0x03e0-0x0cf7 // #1
0x03b0-0x03bb // #2
0x03c0-0x03df // #3
0x0000-0xdfff // #4
0xf000-0xffff // #5

Obviously, region number #4 is erroneous as it overlaps with regions #0..3. 
The code in coalesce_windows() in arch/x86/pci/acpi.c attempts to recover from 
such kind of BIOS bugs by merging the overlapping regions. Current code 
expands region #0 to 0x0000-0xdffff and makes region #4 ignored. As a result, 
overlap of the expanded region #0 with regions #1..3 remains undetected (as 
the inner loop already compared them with region #0). As a result, regions 
#1..3 are inserted into the resource tree even though they overlap with 
adjusted region #0 - which later results in resource conflicts for PCI devices 
with IO ports in one of those regions (e.g., for an PCI IDE controller in 
legacy mode - which has port 0x3f6). The kernel then refuses to initialize 
these devices.

The fix: instead of expanding res1 and ignoring res2, do the opposite. The 
res2 window is yet to be compared against all windows between res1 and res2 
(regions #1..3 in the above example), so the resulting resource map will 
include just the expanded region - and will ignore any overlapping ones.

Signed-off-by: Alexey Neyman <stilor@att.net>
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diff --git a/arch/x86/pci/acpi.c b/arch/x86/pci/acpi.c
index b30e937..7fb24e5 100644
--- a/arch/x86/pci/acpi.c
+++ b/arch/x86/pci/acpi.c
@@ -354,12 +354,12 @@ static void coalesce_windows(struct pci_root_info *info, unsigned long type)
 			 * the kernel resource tree doesn't allow overlaps.
 			 */
 			if (resource_overlaps(res1, res2)) {
-				res1->start = min(res1->start, res2->start);
-				res1->end = max(res1->end, res2->end);
+				res2->start = min(res1->start, res2->start);
+				res2->end = max(res1->end, res2->end);
 				dev_info(&info->bridge->dev,
 					 "host bridge window expanded to %pR; %pR ignored\n",
-					 res1, res2);
-				res2->flags = 0;
+					 res2, res1);
+				res1->flags = 0;
 			}
 		}
 	}

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