[PATCH] drm/i915/hwmon: Don't use FIELD_PREP

[Ashutosh Dixit]

FIELD_PREP and REG_FIELD_PREP have checks requiring a compile time constant
mask. When the mask comes in as the argument of a function these checks can
can fail depending on the compiler (gcc vs clang), optimization level,
etc. Use a simpler version of FIELD_PREP which skips these checks. The
checks are not needed because the mask is formed using REG_GENMASK (so is
actually a compile time constant).

v2: Split REG_FIELD_PREP into a macro with checks and one without and use
    the one without checks in i915_hwmon.c (Gwan-gyeong Mun)

Bug: https://gitlab.freedesktop.org/drm/intel/-/issues/7354
Signed-off-by: Ashutosh Dixit <ashutosh.dixit at intel.com>
---
 drivers/gpu/drm/i915/i915_hwmon.c    |  2 +-
 drivers/gpu/drm/i915/i915_reg_defs.h | 17 +++++++++++------
 2 files changed, 12 insertions(+), 7 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_hwmon.c b/drivers/gpu/drm/i915/i915_hwmon.c
index 9e97814930254..ae435b035229a 100644
--- a/drivers/gpu/drm/i915/i915_hwmon.c
+++ b/drivers/gpu/drm/i915/i915_hwmon.c
@@ -112,7 +112,7 @@ hwm_field_scale_and_write(struct hwm_drvdata *ddat, i915_reg_t rgadr,
 	nval = DIV_ROUND_CLOSEST_ULL((u64)lval << nshift, scale_factor);
 
 	bits_to_clear = field_msk;
-	bits_to_set = FIELD_PREP(field_msk, nval);
+	bits_to_set = __REG_FIELD_PREP(field_msk, nval);
 
 	hwm_locked_with_pm_intel_uncore_rmw(ddat, rgadr,
 					    bits_to_clear, bits_to_set);
diff --git a/drivers/gpu/drm/i915/i915_reg_defs.h b/drivers/gpu/drm/i915/i915_reg_defs.h
index f1859046a9c48..dddacc8d48928 100644
--- a/drivers/gpu/drm/i915/i915_reg_defs.h
+++ b/drivers/gpu/drm/i915/i915_reg_defs.h
@@ -67,12 +67,17 @@
  *
  * @return: @__val masked and shifted into the field defined by @__mask.
  */
-#define REG_FIELD_PREP(__mask, __val)						\
-	((u32)((((typeof(__mask))(__val) << __bf_shf(__mask)) & (__mask)) +	\
-	       BUILD_BUG_ON_ZERO(!__is_constexpr(__mask)) +		\
-	       BUILD_BUG_ON_ZERO((__mask) == 0 || (__mask) > U32_MAX) +		\
-	       BUILD_BUG_ON_ZERO(!IS_POWER_OF_2((__mask) + (1ULL << __bf_shf(__mask)))) + \
-	       BUILD_BUG_ON_ZERO(__builtin_choose_expr(__is_constexpr(__val), (~((__mask) >> __bf_shf(__mask)) & (__val)), 0))))
+#define __REG_FIELD_PREP_CHK(__mask, __val) \
+	(BUILD_BUG_ON_ZERO(!__is_constexpr(__mask)) + \
+	 BUILD_BUG_ON_ZERO((__mask) == 0 || (__mask) > U32_MAX) + \
+	 BUILD_BUG_ON_ZERO(!IS_POWER_OF_2((__mask) + (1ULL << __bf_shf(__mask)))) + \
+	 BUILD_BUG_ON_ZERO(__builtin_choose_expr(__is_constexpr(__val), (~((__mask) >> __bf_shf(__mask)) & (__val)), 0)))
+
+#define __REG_FIELD_PREP(__mask, __val) \
+	((u32)((((typeof(__mask))(__val) << __bf_shf(__mask)) & (__mask))))
+
+#define REG_FIELD_PREP(__mask, __val) \
+	(__REG_FIELD_PREP(__mask, __val) + __REG_FIELD_PREP_CHK(__mask, __val))
 
 /**
  * REG_FIELD_GET() - Extract a u32 bitfield value
-- 
2.38.0