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, 12 insertions, 0 deletions

diff --git a/common/host_command.c b/common/host_command.c
index 51d1a9cf97..0a6226b59e 100644
--- a/common/host_command.c
+++ b/common/host_command.c
@@ -81,6 +81,18 @@ uint8_t *host_get_memmap(int offset)
 #endif
 }
 
+static struct mutex memmap_write_mutex;
+
+void host_lock_memmap()
+{
+	mutex_lock(&memmap_write_mutex);
+}
+
+void host_unlock_memmap()
+{
+	mutex_unlock(&memmap_write_mutex);
+}
+
 int host_get_vboot_mode(void)
 {
 	return g_vboot_mode;