ACPI: EC: Do the byte access with a fast path

Specification allows only byte access for EC region, so
make it separate from bug-compatible multi-byte access.
Also do not allow return of garbage in supplied *value.

Reference: http://bugzilla.kernel.org/show_bug.cgi?id=9341

Signed-off-by: Alexey Starikovskiy <astarikovskiy@suse.de>
Signed-off-by: Len Brown <len.brown@intel.com>

1 files changed, 11 insertions, 4 deletions

diff --git a/drivers/acpi/ec.c b/drivers/acpi/ec.c
index d411017f8c06..63862dfe347b 100644
--- a/drivers/acpi/ec.c
+++ b/drivers/acpi/ec.c
@@ -563,7 +563,7 @@ acpi_ec_space_handler(u32 function, acpi_physical_address address,
                       void *handler_context, void *region_context)
 {
         struct acpi_ec *ec = handler_context;
-        int result = 0, i = 0;
+        int result = 0, i;
         u8 temp = 0;
 
         if ((address > 0xFF) || !value || !handler_context)
@@ -575,7 +575,16 @@ acpi_ec_space_handler(u32 function, acpi_physical_address address,
         if (bits != 8 && acpi_strict)
                 return AE_BAD_PARAMETER;
 
-        while (bits - i > 0) {
+        if (function == ACPI_READ) {
+                result = acpi_ec_read(ec, address, &temp);
+                *value = temp;
+        } else {
+                temp = 0xff & (*value);
+                result = acpi_ec_write(ec, address, temp);
+        }
+
+        for (i = 8; unlikely(bits - i > 0); i += 8) {
+                ++address;
                 if (function == ACPI_READ) {
                         result = acpi_ec_read(ec, address, &temp);
                         (*value) |= ((acpi_integer)temp) << i;
@@ -583,8 +592,6 @@ acpi_ec_space_handler(u32 function, acpi_physical_address address,
                         temp = 0xff & ((*value) >> i);
                         result = acpi_ec_write(ec, address, temp);
                 }
-                i += 8;
-                ++address;
         }
 
         switch (result) {