drm/i915: fix up tiling/fence reg setup on i8xx class hw

This fixes all the tiling problems with the 2d ddx. glxgears still doesn't work.
Changes:

- fix a copy&paste error in i8xx fence reg setup. It resulted in an at most a
  512KB offset of the fence reg window, so was only visible sometimes.
- add tests for stride and object size constrains (also for i915 and 1965 class
  hw). Userspace seems to have an of-by-one bug there, which changes the fence
  size by at most 512KB due to an overflow.
- because i8xx hw is quite old (and therefore not as well-tested) I left 2 debug
  WARN_ONs in the i8xx fence reg setup code to hopefully catch any further
  overflows in the bit-fields. Lastly there's one small change to make the
  alignment checks more consistent.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=20289
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Eric Anholt <eric@anholt.net>
diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
index 377cc58..83357b0 100644
--- a/drivers/gpu/drm/i915/i915_reg.h
+++ b/drivers/gpu/drm/i915/i915_reg.h
@@ -190,6 +190,8 @@
 #define   I830_FENCE_SIZE_BITS(size)	((ffs((size) >> 19) - 1) << 8)
 #define   I830_FENCE_PITCH_SHIFT	4
 #define   I830_FENCE_REG_VALID		(1<<0)
+#define   I830_FENCE_MAX_PITCH_VAL	0x10
+#define   I830_FENCE_MAX_SIZE_VAL	(1<<8)
 
 #define   I915_FENCE_START_MASK		0x0ff00000
 #define   I915_FENCE_SIZE_BITS(size)	((ffs((size) >> 20) - 1) << 8)
@@ -198,6 +200,7 @@
 #define   I965_FENCE_PITCH_SHIFT	2
 #define   I965_FENCE_TILING_Y_SHIFT	1
 #define   I965_FENCE_REG_VALID		(1<<0)
+#define   I965_FENCE_MAX_PITCH_VAL	0x0400
 
 /*
  * Instruction and interrupt control regs