drm/i915/selftests: Ensure we don't clamp a random offset to 32b

Specify that we do want a 64b value for sizeof(u32) as we want to
compute the mask of the upper 62bits.

v2: Use round_down() for automatic type promotion
Signed-off-by: NChris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Reviewed-by: NMika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190710161413.7115-1-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/gem/selftests/i915_gem_context.c

@@ -1539,7 +1539,7 @@ static int igt_vm_isolation(void *arg)
 
 			div64_u64_rem(i915_prandom_u64_state(&prng),
 				      vm_total, &offset);
-			offset &= -sizeof(u32);
+			offset = round_down(offset, alignof_dword);
 			offset += I915_GTT_PAGE_SIZE;
 
 			err = write_to_scratch(ctx_a, engine,

drivers/gpu/drm/i915/gt/intel_gpu_commands.h

@@ -7,6 +7,13 @@
 #ifndef _INTEL_GPU_COMMANDS_H_
 #define _INTEL_GPU_COMMANDS_H_
 
+/*
+ * Target address alignments required for GPU access e.g.
+ * MI_STORE_DWORD_IMM.
+ */
+#define alignof_dword 4
+#define alignof_qword 8
+
 /*
  * Instruction field definitions used by the command parser
  */