x86/sysfb_efi: Fix valid BAR address range check

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.

Signed-off-by: Wang YanQing <udknight@gmail.com>
[ Rewrote changelog. ]
Signed-off-by: Matt Fleming <matt@codeblueprint.co.uk>
Reviewed-by: Peter Jones <pjones@redhat.com>
Cc: <stable@vger.kernel.org>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: David Herrmann <dh.herrmann@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tomi Valkeinen <tomi.valkeinen@ti.com>
Cc: linux-efi@vger.kernel.org
Link: http://lkml.kernel.org/r/1462454061-21561-2-git-send-email-matt@codeblueprint.co.uk
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 12 insertions, 2 deletions

diff --git a/arch/x86/kernel/sysfb_efi.c b/arch/x86/kernel/sysfb_efi.c
index b285d4e8c68e..5da924bbf0a0 100644
--- a/arch/x86/kernel/sysfb_efi.c
+++ b/arch/x86/kernel/sysfb_efi.c
@@ -106,14 +106,24 @@ static int __init efifb_set_system(const struct dmi_system_id *id)
                                         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;
                                         }
                                 }
                         }