ACPI: Support accessing memmap data over ACPI CMD / DATA portsstabilize-6915.B

Some platforms are unable to access the 900h-9ffh region over LPC and
must instead access memmap data through the ACPI CMD / DATA ports. To
avoid racing with data updates, disallow changes to multi-byte memmap
data while in burst mode.

Linux currently enables burst mode when accessing multi-byte data and
disables it immediately afterward, though the ACPI spec defines burst mode
in a more general way.

BUG=chrome-os-partner:38224
TEST=Manual on Samus. Undefine LPC_MEMMAP and modify asl to move memmap
data to ERAM at offset 0x20. Verify system boots cleanly and battery
status is updated immediately on plug / unplug.
BRANCH=None

Change-Id: Ib848bdb491fdfece96ad0cee7a44ba85b4a1a50b
Signed-off-by: Shawn Nematbakhsh <shawnn@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/262072
Reviewed-by: Randall Spangler <rspangler@chromium.org>
Reviewed-by: Duncan Laurie <dlaurie@chromium.org>

1 files changed, 14 insertions, 0 deletions

diff --git a/include/host_command.h b/include/host_command.h
index 4bf903e6ef..f95fe06966 100644
--- a/include/host_command.h
+++ b/include/host_command.h
@@ -124,6 +124,20 @@ struct host_command {
 uint8_t *host_get_memmap(int offset);
 
 /**
+ * Grab the memmap write mutex. This function should be called before
+ * multi-byte variable reads from ACPI, and before updating multi-byte
+ * memmap variables anywhere else.
+ */
+void host_lock_memmap(void);
+
+/**
+ * Release the memmap write mutex. This function should be called once
+ * a multi-byte variable read from ACPI is done, and when updating multi-byte
+ * memmap variables is done.
+ */
+void host_unlock_memmap(void);
+
+/**
  * Process a host command and return its response
  *
  * @param args	        Command handler args