drm/i915/cmdparser: Ignore Length operands during command matching

commit 926abff2 upstream.

Some of the gen instruction macros (e.g. MI_DISPLAY_FLIP) have the
length directly encoded in them. Since these are used directly in
the tables, the Length becomes part of the comparison used for
matching during parsing. Thus, if the cmd being parsed has a
different length to that in the table, it is not matched and the
cmd is accepted via the default variable length path.

Fix by masking out everything except the Opcode in the cmd tables

Cc: Tony Luck <tony.luck@intel.com>
Cc: Dave Airlie <airlied@redhat.com>
Cc: Takashi Iwai <tiwai@suse.de>
Cc: Tyler Hicks <tyhicks@canonical.com>
Signed-off-by: Jon Bloomfield <jon.bloomfield@intel.com>
Reviewed-by: Chris Wilson <chris.p.wilson@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/gpu/drm/i915/i915_cmd_parser.c

@@ -187,7 +187,7 @@ struct drm_i915_cmd_table {
 #define CMD(op, opm, f, lm, fl, ...)				\
 	{							\
 		.flags = (fl) | ((f) ? CMD_DESC_FIXED : 0),	\
-		.cmd = { (op), ~0u << (opm) },			\
+		.cmd = { (op & ~0u << (opm)), ~0u << (opm) },	\
 		.length = { (lm) },				\
 		__VA_ARGS__					\
 	}