PCI: Work around poweroff & suspend-to-RAM issue on Macbook Pro 11

commit 13cfc732160f7bc7e596128ce34cda361c556966 upstream.

Neither soft poweroff (transition to ACPI power state S5) nor
suspend-to-RAM (transition to state S3) works on the Macbook Pro 11,4 and
11,5.

The problem is related to the [mem 0x7fa00000-0x7fbfffff] space.  When we
use that space, e.g., by assigning it to the 00:1c.0 Root Port, the ACPI
Power Management 1 Control Register (PM1_CNT) at [io 0x1804] doesn't work
anymore.

Linux does a soft poweroff (transition to S5) by writing to PM1_CNT.  The
theory about why this doesn't work is:

  - The write to PM1_CNT causes an SMI
  - The BIOS SMI handler depends on something in
    [mem 0x7fa00000-0x7fbfffff]
  - When Linux assigns [mem 0x7fa00000-0x7fbfffff] to the 00:1c.0 Port, it
    covers up whatever the SMI handler uses, so the SMI handler no longer
    works correctly

Reserve the [mem 0x7fa00000-0x7fbfffff] space so we don't assign it to
anything.

This is voodoo programming, since we don't know what the real conflict is,
but we've failed to find the root cause.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=103211
Tested-by: thejoe@gmail.com
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Cc: Rafael J. Wysocki <rafael@kernel.org>
Cc: Lukas Wunner <lukas@wunner.de>
Cc: Chen Yu <yu.c.chen@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

0 files changed, 0 insertions, 0 deletions