Patch "x86/sysfb_efi: Fix valid BAR address range check" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

x86/sysfb_efi: Fix valid BAR address range check

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
x86-sysfb_efi-fix-valid-bar-address-range-check.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Wang YanQing <[email protected]>
Date: Thu, 5 May 2016 14:14:21 +0100
Subject: x86/sysfb_efi: Fix valid BAR address range check

From: Wang YanQing <[email protected]>

commit c10fcb14c7afd6688c7b197a814358fecf244222 upstream.

The code for checking whether a BAR address range is valid will break out of the loop when a start address of 0x0 is encountered.

This behaviour is wrong since by breaking out of the loop we may miss the BAR that describes the EFI frame buffer in a later iteration.

Because of this bug I can't use video=efifb: boot parameter to get efifb on my new ThinkPad E550 for my old linux system hard disk with 3.10 kernel. In 3.10, efifb is the only choice due to DRM/I915 not supporting the GPU.

This patch also add a trivial optimization to break out after we find the frame buffer address range without testing later BARs.

---
 arch/x86/kernel/sysfb_efi.c |   14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

@@ -106,14 +106,24 @@ static int __init efifb_set_system(const
 					continue;
 				for (i = 0; i < DEVICE_COUNT_RESOURCE; i++) {
 					resource_size_t start, end;
+					unsigned long flags;
+
+					flags = pci_resource_flags(dev, i);
+					if (!(flags & IORESOURCE_MEM))
+						continue;
+
+					if (flags & IORESOURCE_UNSET)
+						continue;
+
+					if (pci_resource_len(dev, i) == 0)
+						continue;
 
 					start = pci_resource_start(dev, i);
-					if (start == 0)
-						break;
 					end = pci_resource_end(dev, i);
 					if (screen_info.lfb_base >= start &&
 					    screen_info.lfb_base < end) {
 						found_bar = 1;
+						break;
 					}
 				}
 			}

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/x86-sysfb_efi-fix-valid-bar-address-range-check.patch