Re: Re: [PATCH v3 2/3] bits: Introduce fixed-type BIT

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On Fri, Feb 09, 2024 at 08:53:25AM -0800, Yury Norov wrote:
On Wed, Feb 07, 2024 at 11:45:20PM -0800, Lucas De Marchi wrote:
Implement fixed-type BIT() to help drivers add stricter checks, like was
done for GENMASK.

Signed-off-by: Lucas De Marchi <lucas.demarchi@xxxxxxxxx>
Acked-by: Jani Nikula <jani.nikula@xxxxxxxxx>

So I get v1 from Jan.23 in my mailbox, and this one is v3. Did I miss
a v2? Anyways, please bear my reviewed-by from v1 for this patch.

Jan 23 was actually the v2 and I missed the subject prefix.

My understanding was that you were going to apply this through some
bitmap tree, but checking MAINTAINERS now it seems there's no git tree
associated.  So I will just add your r-b and merge this through
drm-xe.

thanks
Lucas De Marchi


Thanks,
Yury

---
 include/linux/bits.h | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/include/linux/bits.h b/include/linux/bits.h
index bd56f32de44e..811846ce110e 100644
--- a/include/linux/bits.h
+++ b/include/linux/bits.h
@@ -24,12 +24,16 @@
 #define GENMASK_INPUT_CHECK(h, l) \
 	(BUILD_BUG_ON_ZERO(__builtin_choose_expr( \
 		__is_constexpr((l) > (h)), (l) > (h), 0)))
+#define BIT_INPUT_CHECK(type, b) \
+	((BUILD_BUG_ON_ZERO(__builtin_choose_expr( \
+		__is_constexpr(b), (b) >= BITS_PER_TYPE(type), 0))))
 #else
 /*
  * 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
+#define BIT_INPUT_CHECK(type, b) 0
 #endif

 /*
@@ -54,4 +58,17 @@
 #define GENMASK_U32(h, l)	__GENMASK(u32, h, l)
 #define GENMASK_U64(h, l)	__GENMASK(u64, h, l)

+/*
+ * Fixed-type variants of BIT(), with additional checks like __GENMASK().  The
+ * following examples generate compiler warnings due to shift-count-overflow:
+ *
+ * - BIT_U8(8)
+ * - BIT_U32(-1)
+ * - BIT_U32(40)
+ */
+#define BIT_U8(b)		((u8)(BIT_INPUT_CHECK(u8, b) + BIT(b)))
+#define BIT_U16(b)		((u16)(BIT_INPUT_CHECK(u16, b) + BIT(b)))
+#define BIT_U32(b)		((u32)(BIT_INPUT_CHECK(u32, b) + BIT(b)))
+#define BIT_U64(b)		((u64)(BIT_INPUT_CHECK(u64, b) + BIT(b)))
+
 #endif	/* __LINUX_BITS_H */
--
2.43.0



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