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

@@ -1470,42 +1470,43 @@ 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;
-
-		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);
-				ret = -EINVAL;
-				break;
-			}
+	do {
+		u32 length;
 
-			if (desc->flags & CMD_DESC_FIXED)
-				length = desc->length.fixed;
-			else
-				length = (*cmd & desc->length.mask) + LENGTH_BIAS;
+		if (*cmd == MI_BATCH_BUFFER_END)
+			break;
 
-			if ((batch_end - cmd) < length) {
-				DRM_DEBUG("CMD: Command length exceeds batch length: 0x%08X length=%u batchlen=%td\n",
-					  *cmd,
-					  length,
-					  batch_end - cmd);
-				ret = -EINVAL;
-				break;
-			}
+		desc = find_cmd(engine, *cmd, desc, &default_desc);
+		if (!desc) {
+			DRM_DEBUG("CMD: Unrecognized command: 0x%08X\n", *cmd);
+			ret = -EINVAL;
+			break;
+		}
 
-			if (!check_cmd(engine, desc, cmd, length)) {
-				ret = -EACCES;
-				break;
-			}
+		if (desc->flags & CMD_DESC_FIXED)
+			length = desc->length.fixed;
+		else
+			length = (*cmd & desc->length.mask) + LENGTH_BIAS;
 
-			if (cmd_desc_is(desc, MI_BATCH_BUFFER_START)) {
-				ret = check_bbstart(cmd, offset, length, batch_length,
-						    batch_addr, shadow_addr,
-						    jump_whitelist);
-				break;
-			}
+		if ((batch_end - cmd) < length) {
+			DRM_DEBUG("CMD: Command length exceeds batch length: 0x%08X length=%u batchlen=%td\n",
+				  *cmd,
+				  length,
+				  batch_end - cmd);
+			ret = -EINVAL;
+			break;
+		}
+
+		if (!check_cmd(engine, desc, cmd, length)) {
+			ret = -EACCES;
+			break;
+		}
+
+		if (cmd_desc_is(desc, MI_BATCH_BUFFER_START)) {
+			ret = check_bbstart(cmd, offset, length, batch_length,
+					    batch_addr, shadow_addr,
+					    jump_whitelist);
+			break;
 		}
 
 		if (!IS_ERR_OR_NULL(jump_whitelist))
@@ -1518,7 +1519,7 @@ int intel_engine_cmd_parser(struct intel_engine_cs *engine,
 			ret = -EINVAL;
 			break;
 		}
-	}
+	} while (1);
 
 	if (trampoline) {
 		/*