ACPI: EC: Limit burst to 64 bits

access_bit_width field is u8 in ACPICA, thus 256 value written to it
becomes 0, causing divide by zero later.

Proper fix would be to remove access_bit_width at all, just because
we already have access_byte_width, which is access_bit_width / 8.
Limit access width to 64 bit for now.

https://bugzilla.kernel.org/show_bug.cgi?id=15749
fixes regression caused by the fix for:
https://bugzilla.kernel.org/show_bug.cgi?id=14667

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

1 files changed, 11 insertions, 6 deletions

diff --git a/drivers/acpi/acpica/exprep.c b/drivers/acpi/acpica/exprep.c
index a610ebe18edd..2fbfe51fb141 100644
--- a/drivers/acpi/acpica/exprep.c
+++ b/drivers/acpi/acpica/exprep.c
@@ -471,13 +471,18 @@ acpi_status acpi_ex_prep_field_value(struct acpi_create_field_info *info)
                 /* allow full data read from EC address space */
                 if (obj_desc->field.region_obj->region.space_id ==
                         ACPI_ADR_SPACE_EC) {
-                        if (obj_desc->common_field.bit_length > 8)
-                                obj_desc->common_field.access_bit_width =
-                                ACPI_ROUND_UP(obj_desc->common_field.
-                                                        bit_length, 8);
+                        if (obj_desc->common_field.bit_length > 8) {
+                                unsigned width =
+                                        ACPI_ROUND_BITS_UP_TO_BYTES(
+                                        obj_desc->common_field.bit_length);
+                                // access_bit_width is u8, don't overflow it
+                                if (width > 8)
+                                        width = 8;
                                 obj_desc->common_field.access_byte_width =
-                                ACPI_DIV_8(obj_desc->common_field.
-                                                        access_bit_width);
+                                                        width;
+                                obj_desc->common_field.access_bit_width =
+                                                        8 * width;
+                        }
                 }
 
                 ACPI_DEBUG_PRINT((ACPI_DB_BFIELD,