drm/i915: introduce REG_BIT() and REG_GENMASK() to define register contents

Introduce REG_BIT(n) to define register bits and REG_GENMASK(h, l) to
define register bitfield masks.

We define the above as wrappers to BIT() and GENMASK() respectively to
force u32 type to go with our register size, and to add compile time
checks on the bit numbers.

The intention is that these are easier to get right and review against
the spec than hand rolled masks.

Convert power sequencer registers as an example.

v4:
- rebase

v3:
- rename macros to REG_BIT() and REG_GENMASK() to avoid underscore
  prefix and to be in line with kernel macros (Chris)
- add compile time checks (Mika)

v2:
- rename macros to just _BIT() and _MASK() to reduce verbosity

Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Michal Wajdeczko <michal.wajdeczko@intel.com>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Acked-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/787307c0ba9bc23471e5ff1e454b8af35771fa37.1552657998.git.jani.nikula@intel.com

drivers/gpu/drm/i915/i915_reg.h

@@ -25,6 +25,8 @@
 #ifndef _I915_REG_H_
 #define _I915_REG_H_
 
+#include <linux/bits.h>
+
 /**
  * DOC: The i915 register macro definition style guide
  *
@@ -59,15 +61,13 @@
  * significant to least significant bit. Indent the register content macros
  * using two extra spaces between ``#define`` and the macro name.
  *
- * For bit fields, define a ``_MASK`` and a ``_SHIFT`` macro. Define bit field
- * contents so that they are already shifted in place, and can be directly
- * OR'd. For convenience, function-like macros may be used to define bit fields,
- * but do note that the macros may be needed to read as well as write the
- * register contents.
+ * For bit fields, define a ``_MASK`` and a ``_SHIFT`` macro. Use
+ * ``REG_GENMASK()`` to define _MASK. Define bit field contents so that they are
+ * already shifted in place, and can be directly OR'd. For convenience,
+ * function-like macros may be used to define bit fields, but do note that the
+ * macros may be needed to read as well as write the register contents.
  *
- * Define bits using ``(1 << N)`` instead of ``BIT(N)``. We may change this in
- * the future, but this is the prevailing style. Do **not** add ``_BIT`` suffix
- * to the name.
+ * Define bits using ``REG_BIT(N)``. Do **not** add ``_BIT`` suffix to the name.
  *
  * Group the register and its contents together without blank lines, separate
  * from other registers and their contents with one blank line.
@@ -105,8 +105,8 @@
  *  #define _FOO_A                      0xf000
  *  #define _FOO_B                      0xf001
  *  #define FOO(pipe)                   _MMIO_PIPE(pipe, _FOO_A, _FOO_B)
- *  #define   FOO_ENABLE                (1 << 31)
- *  #define   FOO_MODE_MASK             (0xf << 16)
+ *  #define   FOO_ENABLE                REG_BIT(31)
+ *  #define   FOO_MODE_MASK             REG_GENMASK(19, 16)
  *  #define   FOO_MODE_SHIFT            16
  *  #define   FOO_MODE_BAR              (0 << 16)
  *  #define   FOO_MODE_BAZ              (1 << 16)
@@ -116,6 +116,34 @@
  *  #define GEN8_BAR                    _MMIO(0xb888)
  */
 
+/**
+ * REG_BIT() - Prepare a u32 bit value
+ * @__n: 0-based bit number
+ *
+ * Local wrapper for BIT() to force u32, with compile time checks.
+ *
+ * @return: Value with bit @__n set.
+ */
+#define REG_BIT(__n)							\
+	((u32)(BIT(__n) +						\
+	       BUILD_BUG_ON_ZERO(__builtin_constant_p(__n) &&		\
+				 ((__n) < 0 || (__n) > 31))))
+
+/**
+ * REG_GENMASK() - Prepare a continuous u32 bitmask
+ * @__high: 0-based high bit
+ * @__low: 0-based low bit
+ *
+ * Local wrapper for GENMASK() to force u32, with compile time checks.
+ *
+ * @return: Continuous bitmask from @__high to @__low, inclusive.
+ */
+#define REG_GENMASK(__high, __low)					\
+	((u32)(GENMASK(__high, __low) +					\
+	       BUILD_BUG_ON_ZERO(__builtin_constant_p(__high) &&	\
+				 __builtin_constant_p(__low) &&		\
+				 ((__low) < 0 || (__high) > 31 || (__low) > (__high)))))
+
 typedef struct {
 	u32 reg;
 } i915_reg_t;
@@ -4692,18 +4720,18 @@ enum {
 
 #define _PP_STATUS			0x61200
 #define PP_STATUS(pps_idx)		_MMIO_PPS(pps_idx, _PP_STATUS)
-#define   PP_ON				(1 << 31)
+#define   PP_ON				REG_BIT(31)
 
 #define _PP_CONTROL_1			0xc7204
 #define _PP_CONTROL_2			0xc7304
 #define ICP_PP_CONTROL(x)		_MMIO(((x) == 1) ? _PP_CONTROL_1 : \
 					      _PP_CONTROL_2)
-#define  POWER_CYCLE_DELAY_MASK	(0x1f << 4)
+#define  POWER_CYCLE_DELAY_MASK		REG_GENMASK(8, 4)
 #define  POWER_CYCLE_DELAY_SHIFT	4
-#define  VDD_OVERRIDE_FORCE		(1 << 3)
-#define  BACKLIGHT_ENABLE		(1 << 2)
-#define  PWR_DOWN_ON_RESET		(1 << 1)
-#define  PWR_STATE_TARGET		(1 << 0)
+#define  VDD_OVERRIDE_FORCE		REG_BIT(3)
+#define  BACKLIGHT_ENABLE		REG_BIT(2)
+#define  PWR_DOWN_ON_RESET		REG_BIT(1)
+#define  PWR_STATE_TARGET		REG_BIT(0)
 /*
  * Indicates that all dependencies of the panel are on:
  *
@@ -4711,14 +4739,14 @@ enum {
  * - pipe enabled
  * - LVDS/DVOB/DVOC on
  */
-#define   PP_READY			(1 << 30)
+#define   PP_READY			REG_BIT(30)
+#define   PP_SEQUENCE_MASK		REG_GENMASK(29, 28)
 #define   PP_SEQUENCE_NONE		(0 << 28)
 #define   PP_SEQUENCE_POWER_UP		(1 << 28)
 #define   PP_SEQUENCE_POWER_DOWN	(2 << 28)
-#define   PP_SEQUENCE_MASK		(3 << 28)
 #define   PP_SEQUENCE_SHIFT		28
-#define   PP_CYCLE_DELAY_ACTIVE		(1 << 27)
-#define   PP_SEQUENCE_STATE_MASK	0x0000000f
+#define   PP_CYCLE_DELAY_ACTIVE		REG_BIT(27)
+#define   PP_SEQUENCE_STATE_MASK	REG_GENMASK(3, 0)
 #define   PP_SEQUENCE_STATE_OFF_IDLE	(0x0 << 0)
 #define   PP_SEQUENCE_STATE_OFF_S0_1	(0x1 << 0)
 #define   PP_SEQUENCE_STATE_OFF_S0_2	(0x2 << 0)
@@ -4731,41 +4759,41 @@ enum {
 
 #define _PP_CONTROL			0x61204
 #define PP_CONTROL(pps_idx)		_MMIO_PPS(pps_idx, _PP_CONTROL)
+#define  PANEL_UNLOCK_MASK		REG_GENMASK(31, 16)
 #define  PANEL_UNLOCK_REGS		(0xabcd << 16)
-#define  PANEL_UNLOCK_MASK		(0xffff << 16)
-#define  BXT_POWER_CYCLE_DELAY_MASK	0x1f0
+#define  BXT_POWER_CYCLE_DELAY_MASK	REG_GENMASK(8, 4)
 #define  BXT_POWER_CYCLE_DELAY_SHIFT	4
-#define  EDP_FORCE_VDD			(1 << 3)
-#define  EDP_BLC_ENABLE			(1 << 2)
-#define  PANEL_POWER_RESET		(1 << 1)
-#define  PANEL_POWER_ON			(1 << 0)
+#define  EDP_FORCE_VDD			REG_BIT(3)
+#define  EDP_BLC_ENABLE			REG_BIT(2)
+#define  PANEL_POWER_RESET		REG_BIT(1)
+#define  PANEL_POWER_ON			REG_BIT(0)
 
 #define _PP_ON_DELAYS			0x61208
 #define PP_ON_DELAYS(pps_idx)		_MMIO_PPS(pps_idx, _PP_ON_DELAYS)
 #define  PANEL_PORT_SELECT_SHIFT	30
-#define  PANEL_PORT_SELECT_MASK		(3 << 30)
+#define  PANEL_PORT_SELECT_MASK		REG_GENMASK(31, 30)
 #define  PANEL_PORT_SELECT_LVDS		(0 << 30)
 #define  PANEL_PORT_SELECT_DPA		(1 << 30)
 #define  PANEL_PORT_SELECT_DPC		(2 << 30)
 #define  PANEL_PORT_SELECT_DPD		(3 << 30)
 #define  PANEL_PORT_SELECT_VLV(port)	((port) << 30)
-#define  PANEL_POWER_UP_DELAY_MASK	0x1fff0000
+#define  PANEL_POWER_UP_DELAY_MASK	REG_GENMASK(28, 16)
 #define  PANEL_POWER_UP_DELAY_SHIFT	16
-#define  PANEL_LIGHT_ON_DELAY_MASK	0x1fff
+#define  PANEL_LIGHT_ON_DELAY_MASK	REG_GENMASK(12, 0)
 #define  PANEL_LIGHT_ON_DELAY_SHIFT	0
 
 #define _PP_OFF_DELAYS			0x6120C
 #define PP_OFF_DELAYS(pps_idx)		_MMIO_PPS(pps_idx, _PP_OFF_DELAYS)
-#define  PANEL_POWER_DOWN_DELAY_MASK	0x1fff0000
+#define  PANEL_POWER_DOWN_DELAY_MASK	REG_GENMASK(28, 16)
 #define  PANEL_POWER_DOWN_DELAY_SHIFT	16
-#define  PANEL_LIGHT_OFF_DELAY_MASK	0x1fff
+#define  PANEL_LIGHT_OFF_DELAY_MASK	REG_GENMASK(12, 0)
 #define  PANEL_LIGHT_OFF_DELAY_SHIFT	0
 
 #define _PP_DIVISOR			0x61210
 #define PP_DIVISOR(pps_idx)		_MMIO_PPS(pps_idx, _PP_DIVISOR)
-#define  PP_REFERENCE_DIVIDER_MASK	0xffffff00
+#define  PP_REFERENCE_DIVIDER_MASK	REG_GENMASK(31, 8)
 #define  PP_REFERENCE_DIVIDER_SHIFT	8
-#define  PANEL_POWER_CYCLE_DELAY_MASK	0x1f
+#define  PANEL_POWER_CYCLE_DELAY_MASK	REG_GENMASK(4, 0)
 #define  PANEL_POWER_CYCLE_DELAY_SHIFT	0
 
 /* Panel fitting */