drm/i915: Disable gpu relocations

Media userspace was the last userspace to still use them, and they
converted now too:

https://github.com/intel/media-driver/commit/144020c37770083974bedf59902b70b8f444c799

This means no reason anymore to make relocations faster than they've
been for the first 9 years of gem. This code was added in

commit 7dd4f672
Author: Chris Wilson <chris@chris-wilson.co.uk>
Date:   Fri Jun 16 15:05:24 2017 +0100

    drm/i915: Async GPU relocation processing

Furthermore there's pretty strong indications it's buggy, since the
code to use it by default as the only option had to be reverted:

commit ad5d95e4
Author: Dave Airlie <airlied@redhat.com>
Date:   Tue Sep 8 15:41:17 2020 +1000

    Revert "drm/i915/gem: Async GPU relocations only"

This code just disables gpu relocations, leaving the garbage
collection for later patches and more importantly, much less confusing
diff. Also given how much headaches this code has caused in the past,
letting this soak for a bit seems justified.
Acked-by: Dave Airlie <airlied@redhat.com>
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Cc: Jon Bloomfield <jon.bloomfield@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: "Thomas Hellström" <thomas.hellstrom@linux.intel.com>
Cc: Matthew Auld <matthew.auld@intel.com>
Cc: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Cc: Dave Airlie <airlied@redhat.com>
Cc: Jason Ekstrand <jason@jlekstrand.net>
Link: https://patchwork.freedesktop.org/patch/msgid/20210803124833.3817354-1-daniel.vetter@ffwll.ch

drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c

@@ -1577,7 +1577,7 @@ static int __reloc_entry_gpu(struct i915_execbuffer *eb,
 	return true;
 }
 
-static int reloc_entry_gpu(struct i915_execbuffer *eb,
+static int __maybe_unused reloc_entry_gpu(struct i915_execbuffer *eb,
 			    struct i915_vma *vma,
 			    u64 offset,
 			    u64 target_addr)
@@ -1599,32 +1599,25 @@ relocate_entry(struct i915_vma *vma,
 {
 	u64 target_addr = relocation_target(reloc, target);
 	u64 offset = reloc->offset;
-	int reloc_gpu = reloc_entry_gpu(eb, vma, offset, target_addr);
-
-	if (reloc_gpu < 0)
-		return reloc_gpu;
-
-	if (!reloc_gpu) {
-		bool wide = eb->reloc_cache.use_64bit_reloc;
-		void *vaddr;
+	bool wide = eb->reloc_cache.use_64bit_reloc;
+	void *vaddr;
 
 repeat:
-		vaddr = reloc_vaddr(vma->obj, eb,
-				    offset >> PAGE_SHIFT);
-		if (IS_ERR(vaddr))
-			return PTR_ERR(vaddr);
-
-		GEM_BUG_ON(!IS_ALIGNED(offset, sizeof(u32)));
-		clflush_write32(vaddr + offset_in_page(offset),
-				lower_32_bits(target_addr),
-				eb->reloc_cache.vaddr);
-
-		if (wide) {
-			offset += sizeof(u32);
-			target_addr >>= 32;
-			wide = false;
-			goto repeat;
-		}
+	vaddr = reloc_vaddr(vma->obj, eb,
+			    offset >> PAGE_SHIFT);
+	if (IS_ERR(vaddr))
+		return PTR_ERR(vaddr);
+
+	GEM_BUG_ON(!IS_ALIGNED(offset, sizeof(u32)));
+	clflush_write32(vaddr + offset_in_page(offset),
+			lower_32_bits(target_addr),
+			eb->reloc_cache.vaddr);
+
+	if (wide) {
+		offset += sizeof(u32);
+		target_addr >>= 32;
+		wide = false;
+		goto repeat;
 	}
 
 	return target->node.start | UPDATE;