drm/i915: Don't use GPU relocations prior to cmdparser stalls

If we are using the cmdparser, we will have to copy the batch and so
stall for the relocations. Rather than prolong that stall by adding more
relocation requests, just use CPU relocations and do the stall upfront.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20170826135620.25949-1-chris@chris-wilson.co.uk
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>

drivers/gpu/drm/i915/i915_gem_execbuffer.c

@@ -268,6 +268,11 @@ static inline u64 gen8_noncanonical_addr(u64 address)
 	return address & GENMASK_ULL(GEN8_HIGH_ADDRESS_BIT, 0);
 }
 
+static inline bool eb_use_cmdparser(const struct i915_execbuffer *eb)
+{
+	return eb->engine->needs_cmd_parser && eb->batch_len;
+}
+
 static int eb_create(struct i915_execbuffer *eb)
 {
 	if (!(eb->args->flags & I915_EXEC_HANDLE_LUT)) {
@@ -1159,6 +1164,10 @@ static u32 *reloc_gpu(struct i915_execbuffer *eb,
 	if (unlikely(!cache->rq)) {
 		int err;
 
+		/* If we need to copy for the cmdparser, we will stall anyway */
+		if (eb_use_cmdparser(eb))
+			return ERR_PTR(-EWOULDBLOCK);
+
 		err = __reloc_gpu_alloc(eb, vma, len);
 		if (unlikely(err))
 			return ERR_PTR(err);
@@ -2293,7 +2302,7 @@ i915_gem_do_execbuffer(struct drm_device *dev,
 		goto err_vma;
 	}
 
-	if (eb.engine->needs_cmd_parser && eb.batch_len) {
+	if (eb_use_cmdparser(&eb)) {
 		struct i915_vma *vma;
 
 		vma = eb_parse(&eb, drm_is_current_master(file));