linux-kernel - [PATCH v2 1/5] wordpart.h: Add REPEAT_BYTE

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Date: Mon, 17 Jun 2024 12:18:37 +0100
From: Mark Rutland <mark.rutland@....com>
To: linux-arm-kernel@...ts.infradead.org
Cc: alexandru.elisei@....com,
	catalin.marinas@....com,
	linux-kernel@...r.kernel.org,
	mark.rutland@....com,
	maz@...nel.org,
	tglx@...utronix.de,
	will@...nel.org
Subject: [PATCH v2 1/5] wordpart.h: Add REPEAT_BYTE_U32()

In some cases it's necessary to replicate a byte across a u32 value, for
which REPEAT_BYTE() would be helpful. Currently this requires explicit
masking of the result to avoid sparse warnings, as e.g.

    (u32)REPEAT_BYTE(0xa0))

... will result in a warning:

    cast truncates bits from constant value (a0a0a0a0a0a0a0a0 becomes a0a0a0a0)

Add a new REPEAT_BYTE_U32() which does the necessary masking internally,
so that we don't need to duplicate this for every usage.

Signed-off-by: Mark Rutland <mark.rutland@....com>
Cc: Alexandru Elisei <alexandru.elisei@....com>
Cc: Catalin Marinas <catalin.marinas@....com>
Cc: Marc Zyngier <maz@...nel.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Will Deacon <will@...nel.org>
---
 include/linux/wordpart.h | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/include/linux/wordpart.h b/include/linux/wordpart.h
index 4ca1ba66d2f07..5a7b97bb7c956 100644
--- a/include/linux/wordpart.h
+++ b/include/linux/wordpart.h
@@ -39,6 +39,14 @@
  */
 #define REPEAT_BYTE(x)	((~0ul / 0xff) * (x))
 
+/**
+ * REPEAT_BYTE_U32 - repeat the value @x multiple times as a u32 value
+ * @x: value to repeat
+ *
+ * NOTE: @x is not checked for > 0xff; larger values produce odd results.
+ */
+#define REPEAT_BYTE_U32(x)	lower_32_bits(REPEAT_BYTE(x))
+
 /* Set bits in the first 'n' bytes when loaded from memory */
 #ifdef __LITTLE_ENDIAN
 #  define aligned_byte_mask(n) ((1UL << 8*(n))-1)
-- 
2.30.2