iommu/io-pgtable-arm-v7s: Clarify LVL_SHIFT/BITS macro

The current _ARM_V7S_LVL_BITS/ARM_V7S_LVL_SHIFT use a formula to calculate
the corresponding value for level1 and level2 to pretend the code sane.
Actually their level1 and level2 values are different from each other.
This patch only clarify the two macro. No functional change.
Suggested-by: NRobin Murphy <robin.murphy@arm.com>
Signed-off-by: NYong Wu <yong.wu@mediatek.com>
Reviewed-by: NRobin Murphy <robin.murphy@arm.com>
Reviewed-by: NTomasz Figa <tfiga@chromium.org>
Link: https://lore.kernel.org/r/20210111111914.22211-12-yong.wu@mediatek.comSigned-off-by: NWill Deacon <will@kernel.org>

drivers/iommu/io-pgtable-arm-v7s.c

@@ -44,13 +44,11 @@
 
 /*
  * We have 32 bits total; 12 bits resolved at level 1, 8 bits at level 2,
- * and 12 bits in a page. With some carefully-chosen coefficients we can
- * hide the ugly inconsistencies behind these macros and at least let the
- * rest of the code pretend to be somewhat sane.
+ * and 12 bits in a page.
  */
 #define ARM_V7S_ADDR_BITS		32
-#define _ARM_V7S_LVL_BITS(lvl)		(16 - (lvl) * 4)
-#define ARM_V7S_LVL_SHIFT(lvl)		(ARM_V7S_ADDR_BITS - (4 + 8 * (lvl)))
+#define _ARM_V7S_LVL_BITS(lvl)		((lvl) == 1 ? 12 : 8)
+#define ARM_V7S_LVL_SHIFT(lvl)		((lvl) == 1 ? 20 : 12)
 #define ARM_V7S_TABLE_SHIFT		10
 
 #define ARM_V7S_PTES_PER_LVL(lvl)	(1 << _ARM_V7S_LVL_BITS(lvl))