linux/arch
Lukas Wunner 850c321027 x86/quirks: Reintroduce scanning of secondary buses
We used to scan secondary buses until the following commit that
was applied in 2009:

  8659c406ad ("x86: only scan the root bus in early PCI quirks")

which commit constrained early quirks to the root bus only. Its
motivation was to prevent application of the nvidia_bugs quirk
on secondary buses.

We're about to add a quirk to reset the Broadcom 4331 wireless card on
2011/2012 Macs, which is located on a secondary bus behind a PCIe root
port. To facilitate that, reintroduce scanning of secondary buses.

The commit message of 8659c406ad notes that scanning only the root bus
"saves quite some unnecessary scanning work". The algorithm used prior
to 8659c406ad was particularly time consuming because it scanned
buses 0 to 31 brute force. To avoid lengthening boot time, employ a
recursive strategy which only scans buses that are actually reachable
from the root bus.

Yinghai Lu pointed out that the secondary bus number read from a
bridge's config space may be invalid, in particular a value of 0 would
cause an infinite loop. The PCI core goes beyond that and recurses to a
child bus only if its bus number is greater than the parent bus number
(see pci_scan_bridge()). Since the root bus is numbered 0, this implies
that secondary buses may not be 0. Do the same on early scanning.

If this algorithm is found to significantly impact boot time or cause
infinite loops on broken hardware, it would be possible to limit its
recursion depth: The Broadcom 4331 quirk applies at depth 1, all others
at depth 0, so the bus need not be scanned deeper than that for now. An
alternative approach would be to revert to scanning only the root bus,
and apply the Broadcom 4331 quirk to the root ports 8086:1c12, 8086:1e12
and 8086:1e16. Apple always positioned the card behind either of these
three ports. The quirk would then check presence of the card in slot 0
below the root port and do its deed.

Signed-off-by: Lukas Wunner <lukas@wunner.de>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Bjorn Helgaas <bhelgaas@google.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Yinghai Lu <yinghai@kernel.org>
Cc: linux-pci@vger.kernel.org
Link: http://lkml.kernel.org/r/f0daa70dac1a9b2483abdb31887173eb6ab77bdf.1465690253.git.lukas@wunner.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2016-07-10 20:13:53 +02:00
..
alpha tree wide: get rid of __GFP_REPEAT for order-0 allocations part I 2016-06-24 17:23:52 -07:00
arc ARC Fix for 4.7-rc6 2016-06-30 09:53:43 -07:00
arm KVM/ARM Fixes for v4.7-rc6: 2016-06-30 17:11:20 +02:00
arm64 arm64: Enable workaround for Cavium erratum 27456 on thunderx-81xx 2016-07-07 18:35:21 +01:00
avr32 tree wide: get rid of __GFP_REPEAT for order-0 allocations part I 2016-06-24 17:23:52 -07:00
blackfin printk/nmi: generic solution for safe printk in NMI 2016-05-20 17:58:30 -07:00
c6x asm-generic patch for 4.7 2016-05-24 15:24:37 -07:00
cris tree wide: get rid of __GFP_REPEAT for order-0 allocations part I 2016-06-24 17:23:52 -07:00
frv tree wide: get rid of __GFP_REPEAT for order-0 allocations part I 2016-06-24 17:23:52 -07:00
h8300 Merge branch 'hash' of git://ftp.sciencehorizons.net/linux 2016-05-28 16:15:25 -07:00
hexagon tree wide: get rid of __GFP_REPEAT for order-0 allocations part I 2016-06-24 17:23:52 -07:00
ia64 fix up initial thread stack pointer vs thread_info confusion 2016-06-24 17:07:33 -07:00
m32r Merge branch 'kbuild' of git://git.kernel.org/pub/scm/linux/kernel/git/mmarek/kbuild 2016-05-26 22:01:22 -07:00
m68k tree wide: get rid of __GFP_REPEAT for order-0 allocations part I 2016-06-24 17:23:52 -07:00
metag tree wide: get rid of __GFP_REPEAT for order-0 allocations part I 2016-06-24 17:23:52 -07:00
microblaze tree wide: get rid of __GFP_REPEAT for order-0 allocations part I 2016-06-24 17:23:52 -07:00
mips MIPS: Fix possible corruption of cache mode by mprotect. 2016-07-02 01:51:39 +02:00
mn10300 Merge branch 'akpm' (patches from Andrew) 2016-06-24 19:08:33 -07:00
nios2 nios2: get rid of superfluous __GFP_REPEAT 2016-06-24 17:23:52 -07:00
openrisc tree wide: get rid of __GFP_REPEAT for order-0 allocations part I 2016-06-24 17:23:52 -07:00
parisc parisc: get rid of superfluous __GFP_REPEAT 2016-06-24 17:23:52 -07:00
powerpc powerpc fixes for 4.7 #5 2016-07-02 17:47:54 -07:00
s390 s390: fix test_fp_ctl inline assembly contraints 2016-06-28 09:24:28 +02:00
score score: get rid of superfluous __GFP_REPEAT 2016-06-24 17:23:52 -07:00
sh sh: get rid of superfluous __GFP_REPEAT 2016-06-24 17:23:52 -07:00
sparc sparc: get rid of superfluous __GFP_REPEAT 2016-06-24 17:23:52 -07:00
tile Merge branch 'akpm' (patches from Andrew) 2016-06-24 19:08:33 -07:00
um tree wide: get rid of __GFP_REPEAT for order-0 allocations part I 2016-06-24 17:23:52 -07:00
unicore32 unicore32: get rid of superfluous __GFP_REPEAT 2016-06-24 17:23:52 -07:00
x86 x86/quirks: Reintroduce scanning of secondary buses 2016-07-10 20:13:53 +02:00
xtensa tree wide: get rid of __GFP_REPEAT for order-0 allocations part I 2016-06-24 17:23:52 -07:00
.gitignore
Kconfig Clarify naming of thread info/stack allocators 2016-06-24 15:09:37 -07:00