From: Vincent Mailhol <mailhol.vincent@xxxxxxxxxx>
Add GENMASK_TYPE() which generalizes __GENMASK() to support different
types, and implement fixed-types versions of GENMASK() based on it.
The fixed-type version allows more strict checks to the min/max values
accepted, which is useful for defining registers like implemented by
i915 and xe drivers with their REG_GENMASK*() macros.
The strict checks rely on shift-count-overflow compiler check to fail
the build if a number outside of the range allowed is passed.
Example:
#define FOO_MASK GENMASK_U32(33, 4)
will generate a warning like:
include/linux/bits.h:51:27: error: right shift count >= width of type [-Werror=shift-count-overflow]
51 | type_max(t) >> (BITS_PER_TYPE(t) - 1 - (h)))))
| ^~
While GENMASK_TYPE() is crafted to cover all variants, including the
already existing GENMASK(), GENMASK_ULL() and GENMASK_U128(), for the
moment, only use it for the newly introduced GENMASK_U*(). The
consolidation will be done in a separate change.
Co-developed-by: Yury Norov <yury.norov@xxxxxxxxx>
Signed-off-by: Yury Norov <yury.norov@xxxxxxxxx>
Signed-off-by: Lucas De Marchi <lucas.demarchi@xxxxxxxxx>
Acked-by: Jani Nikula <jani.nikula@xxxxxxxxx>
Signed-off-by: Vincent Mailhol <mailhol.vincent@xxxxxxxxxx>
---
Changelog:
v6 -> v7:
- Fix grammar in comment: 'GENMASK_U*() depends' -> 'GENMASK_U*()
depend'.
- Fix typo in comment: 'Nethertheless' -> 'Nevertheless'
- Do an artificial early line wrap in comment so that the next
patch only has a one line diff change.
- Re-wrap the comments to the 80th column.
- The patch changed a lot since Yury first version: put myself as
main author and Yury as Co-developer.
- Add a new paragraph to the patch description to explain that
consolidation will be done later.
v5 -> v6:
- No changes.
v4 -> v5:
- Rename GENMASK_t() to GENMASK_TYPE().
- Fix typo in patch description.
- Use tab indentations instead of single space to separate the
macro name from its body.
- s/__GENMASK_U*()/GENMASK_U*()/g in the comment.
- Add a tag to credit myself as Co-developer. Keep Yury as the
main author.
- Modify GENMASK_TYPE() to match the changes made to __GENMASK()
in: https://github.com/norov/linux/commit/1e7933a575ed
- Replace (t)~_ULL(0) with type_max(t). This is OK because
GENMASK_TYPE() is not available in asm.
- linux/const.h and asm/bitsperlong.h are not used anymore. Remove
them.
- Apply GENMASK_TYPE() to GENMASK_U128().
- Remove the unsigned int cast for the U8 and U16 variants. Cast
to the target type instead. Do that cast directly in
GENMASK_TYPE().
v3 -> v4:
- The v3 is one year old. Meanwhile people started using
__GENMASK() directly. So instead of generalizing __GENMASK() to
support different types, add a new GENMASK_t().
- replace ~0ULL by ~_ULL(0). Otherwise, GENMASK_t() would fail in
asm code.
- Make GENMASK_U8() and GENMASK_U16() return an unsigned int. In
v3, due to the integer promotion rules, these were returning a
signed integer. By casting these to unsigned int, at least the
signedness is kept.
---
include/linux/bitops.h | 1 -
include/linux/bits.h | 39 +++++++++++++++++++++++++++++++++++++--
2 files changed, 37 insertions(+), 3 deletions(-)
diff --git a/include/linux/bitops.h b/include/linux/bitops.h
index c1cb53cf2f0f8662ed3e324578f74330e63f935d..9be2d50da09a417966b3d11c84092bb2f4cd0bef 100644
--- a/include/linux/bitops.h
+++ b/include/linux/bitops.h
@@ -8,7 +8,6 @@
#include <uapi/linux/kernel.h>
-#define BITS_PER_TYPE(type) (sizeof(type) * BITS_PER_BYTE)
#define BITS_TO_LONGS(nr) __KERNEL_DIV_ROUND_UP(nr, BITS_PER_TYPE(long))
#define BITS_TO_U64(nr) __KERNEL_DIV_ROUND_UP(nr, BITS_PER_TYPE(u64))
#define BITS_TO_U32(nr) __KERNEL_DIV_ROUND_UP(nr, BITS_PER_TYPE(u32))
diff --git a/include/linux/bits.h b/include/linux/bits.h
index 14fd0ca9a6cd17339dd2f69e449558312a8a001b..beb3ee2f1bc74a9346dd72eb06c722a9bc536051 100644
--- a/include/linux/bits.h
+++ b/include/linux/bits.h
@@ -12,6 +12,7 @@
#define BIT_ULL_MASK(nr) (ULL(1) << ((nr) % BITS_PER_LONG_LONG))
#define BIT_ULL_WORD(nr) ((nr) / BITS_PER_LONG_LONG)
#define BITS_PER_BYTE 8
+#define BITS_PER_TYPE(type) (sizeof(type) * BITS_PER_BYTE)
/*
* Create a contiguous bitmask starting at bit position @l and ending at
@@ -19,16 +20,50 @@
* GENMASK_ULL(39, 21) gives us the 64bit vector 0x000000ffffe00000.
*/
#if !defined(__ASSEMBLY__)
+
+/*
+ * Missing asm support
+ *
+ * GENMASK_U*() depend on BITS_PER_TYPE() which relies on sizeof(),
+ * something not available in asm. Nevertheless, fixed width integers is a C
+ * concept. Assembly code can rely on the long and long long versions instead.
+ */
+
#include <linux/build_bug.h>
#include <linux/compiler.h>
+#include <linux/overflow.h>
+
#define GENMASK_INPUT_CHECK(h, l) BUILD_BUG_ON_ZERO(const_true((l) > (h)))
-#else
+
+/*
+ * Generate a mask for the specified type @t. Additional checks are made to
+ * guarantee the value returned fits in that type, relying on
+ * shift-count-overflow compiler check to detect incompatible arguments.
+ * For example, all these create build errors or warnings:
+ *
+ * - GENMASK(15, 20): wrong argument order
+ * - GENMASK(72, 15): doesn't fit unsigned long
+ * - GENMASK_U32(33, 15): doesn't fit in a u32
+ */
+#define GENMASK_TYPE(t, h, l) \
+ ((t)(GENMASK_INPUT_CHECK(h, l) + \
+ (type_max(t) << (l) & \
+ type_max(t) >> (BITS_PER_TYPE(t) - 1 - (h)))))
+
+#define GENMASK_U8(h, l) GENMASK_TYPE(u8, h, l)
+#define GENMASK_U16(h, l) GENMASK_TYPE(u16, h, l)
+#define GENMASK_U32(h, l) GENMASK_TYPE(u32, h, l)
+#define GENMASK_U64(h, l) GENMASK_TYPE(u64, h, l)
+
+#else /* defined(__ASSEMBLY__) */
+
/*
* BUILD_BUG_ON_ZERO is not available in h files included from asm files,
* disable the input check if that is the case.
*/
#define GENMASK_INPUT_CHECK(h, l) 0
-#endif
+
+#endif /* !defined(__ASSEMBLY__) */
#define GENMASK(h, l) \
(GENMASK_INPUT_CHECK(h, l) + __GENMASK(h, l))
--
2.48.1
