Revert "drm/i915: Skip over MI_NOOP when parsing"

This reverts a6c5e2ae ("drm/i915: Skip over MI_NOOP when parsing").
It complicates the batch parsing code a bit and increases indentation
for no reason other than fast-skipping a command that userspace uses
only rarely.  Sure, there may be IGT tests that fill batches with NOOPs
but that's not a case we should optimize for in the kernel.  We should
optimize for code clarity instead.
Signed-off-by: Jason Ekstrand <jason@jlekstrand.net>
Reviewed-by: Jon Bloomfield <jon.bloomfield@intel.com>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20210714193419.1459723-6-jason@jlekstrand.net

drivers/gpu/drm/i915/i915_cmd_parser.c

@@ -1470,10 +1470,12 @@ int intel_engine_cmd_parser(struct intel_engine_cs *engine,
 	 * space. Parsing should be faster in some cases this way.
 	 */
 	batch_end = cmd + batch_length / sizeof(*batch_end);
-	while (*cmd != MI_BATCH_BUFFER_END) {
-		u32 length = 1;
+	do {
+		u32 length;
+
+		if (*cmd == MI_BATCH_BUFFER_END)
+			break;
 
-		if (*cmd != MI_NOOP) { /* MI_NOOP == 0 */
 		desc = find_cmd(engine, *cmd, desc, &default_desc);
 		if (!desc) {
 			DRM_DEBUG("CMD: Unrecognized command: 0x%08X\n", *cmd);
@@ -1506,7 +1508,6 @@ int intel_engine_cmd_parser(struct intel_engine_cs *engine,
 					    jump_whitelist);
 			break;
 		}
-		}
 
 		if (!IS_ERR_OR_NULL(jump_whitelist))
 			__set_bit(offset, jump_whitelist);
@@ -1518,7 +1519,7 @@ int intel_engine_cmd_parser(struct intel_engine_cs *engine,
 			ret = -EINVAL;
 			break;
 		}
-	}
+	} while (1);
 
 	if (trampoline) {
 		/*