drm/i915/skl: Make 'end' of the DDB allocation entry exclusive

Ville suggested that we should use the same semantics as C arrays to
reduce the number of those pesky +1/-1 in the allocation code.

This patch leaves the debugfs file as is, showing the internal DDB
allocation structure, not the values written in the registers.

v2: Remove the test on ->end in skl_ddb_entry_size() (Ville)

Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Suggested-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Damien Lespiau <damien.lespiau@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index ee744a2..84e8cdb 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -1388,16 +1388,12 @@
 };
 
 struct skl_ddb_entry {
-	uint16_t start, end;	/* in number of blocks */
+	uint16_t start, end;	/* in number of blocks, 'end' is exclusive */
 };
 
 static inline uint16_t skl_ddb_entry_size(const struct skl_ddb_entry *entry)
 {
-	/* end not set, clearly no allocation here. start can be 0 though */
-	if (entry->end == 0)
-		return 0;
-
-	return entry->end - entry->start + 1;
+	return entry->end - entry->start;
 }
 
 static inline bool skl_ddb_entry_equal(const struct skl_ddb_entry *e1,