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Message-Id: <20250623-byeword-update-v2-1-cf1fc08a2e1f@collabora.com>
Date: Mon, 23 Jun 2025 18:05:29 +0200
From: Nicolas Frattaroli <nicolas.frattaroli@...labora.com>
To: Yury Norov <yury.norov@...il.com>,
Rasmus Villemoes <linux@...musvillemoes.dk>,
Jaehoon Chung <jh80.chung@...sung.com>,
Ulf Hansson <ulf.hansson@...aro.org>, Heiko Stuebner <heiko@...ech.de>,
Shreeya Patel <shreeya.patel@...labora.com>,
Mauro Carvalho Chehab <mchehab@...nel.org>,
Sandy Huang <hjc@...k-chips.com>, Andy Yan <andy.yan@...k-chips.com>,
Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>,
David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
Vinod Koul <vkoul@...nel.org>, Kishon Vijay Abraham I <kishon@...nel.org>,
Nicolas Frattaroli <frattaroli.nicolas@...il.com>,
Liam Girdwood <lgirdwood@...il.com>, Mark Brown <broonie@...nel.org>,
Jaroslav Kysela <perex@...ex.cz>, Takashi Iwai <tiwai@...e.com>,
Andrew Lunn <andrew+netdev@...n.ch>,
"David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
Maxime Coquelin <mcoquelin.stm32@...il.com>,
Alexandre Torgue <alexandre.torgue@...s.st.com>,
Shawn Lin <shawn.lin@...k-chips.com>,
Lorenzo Pieralisi <lpieralisi@...nel.org>,
Krzysztof Wilczyński <kwilczynski@...nel.org>,
Manivannan Sadhasivam <mani@...nel.org>, Rob Herring <robh@...nel.org>,
Bjorn Helgaas <bhelgaas@...gle.com>, Chanwoo Choi <cw00.choi@...sung.com>,
MyungJoo Ham <myungjoo.ham@...sung.com>,
Kyungmin Park <kyungmin.park@...sung.com>, Qin Jian <qinjian@...lus1.com>,
Michael Turquette <mturquette@...libre.com>,
Stephen Boyd <sboyd@...nel.org>, Nathan Chancellor <nathan@...nel.org>,
Nick Desaulniers <nick.desaulniers+lkml@...il.com>,
Bill Wendling <morbo@...gle.com>, Justin Stitt <justinstitt@...gle.com>
Cc: kernel@...labora.com, linux-kernel@...r.kernel.org,
linux-mmc@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
linux-rockchip@...ts.infradead.org, linux-media@...r.kernel.org,
dri-devel@...ts.freedesktop.org, linux-phy@...ts.infradead.org,
linux-sound@...r.kernel.org, netdev@...r.kernel.org,
linux-stm32@...md-mailman.stormreply.com, linux-pci@...r.kernel.org,
linux-pm@...r.kernel.org, linux-clk@...r.kernel.org, llvm@...ts.linux.dev,
Nicolas Frattaroli <nicolas.frattaroli@...labora.com>
Subject: [PATCH v2 01/20] bitmap: introduce hardware-specific bitfield
operations
Hardware of various vendors, but very notably Rockchip, often uses
32-bit registers where the upper 16-bit half of the register is a
write-enable mask for the lower half.
This type of hardware setup allows for more granular concurrent register
write access.
Over the years, many drivers have hand-rolled their own version of this
macro, usually without any checks, often called something like
HIWORD_UPDATE or FIELD_PREP_HIWORD, commonly with slightly different
semantics between them.
Clearly there is a demand for such a macro, and thus the demand should
be satisfied in a common header file. As this is a convention that spans
across multiple vendors, and similar conventions may also have
cross-vendor adoption, it's best if it lives in a vendor-agnostic header
file that can be expanded over time.
Add hw_bitfield.h with two macros: FIELD_PREP_WM16, and
FIELD_PREP_WM16_CONST. The latter is a version that can be used in
initializers, like FIELD_PREP_CONST.
Suggested-by: Yury Norov [NVIDIA] <yury.norov@...il.com>
Signed-off-by: Nicolas Frattaroli <nicolas.frattaroli@...labora.com>
---
MAINTAINERS | 1 +
include/linux/hw_bitfield.h | 62 +++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 63 insertions(+)
diff --git a/MAINTAINERS b/MAINTAINERS
index 41f13ccef4c84dcb1762c166553a2dc35704f211..8d2cf600d5cd722b5b08e81b6b24338fdc044240 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -4187,6 +4187,7 @@ F: include/linux/bits.h
F: include/linux/cpumask.h
F: include/linux/cpumask_types.h
F: include/linux/find.h
+F: include/linux/hw_bitfield.h
F: include/linux/nodemask.h
F: include/linux/nodemask_types.h
F: include/vdso/bits.h
diff --git a/include/linux/hw_bitfield.h b/include/linux/hw_bitfield.h
new file mode 100644
index 0000000000000000000000000000000000000000..df202e167ce487122e4440962eacb2e44817ad9f
--- /dev/null
+++ b/include/linux/hw_bitfield.h
@@ -0,0 +1,62 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * Copyright (C) 2025, Collabora Ltd.
+ */
+
+#ifndef _LINUX_HW_BITFIELD_H
+#define _LINUX_HW_BITFIELD_H
+
+#include <linux/bitfield.h>
+#include <linux/build_bug.h>
+#include <linux/limits.h>
+
+/**
+ * FIELD_PREP_WM16() - prepare a bitfield element with a mask in the upper half
+ * @_mask: shifted mask defining the field's length and position
+ * @_val: value to put in the field
+ *
+ * FIELD_PREP_WM16() masks and shifts up the value, as well as bitwise ORs the
+ * result with the mask shifted up by 16.
+ *
+ * This is useful for a common design of hardware registers where the upper
+ * 16-bit half of a 32-bit register is used as a write-enable mask. In such a
+ * register, a bit in the lower half is only updated if the corresponding bit
+ * in the upper half is high.
+ */
+#define FIELD_PREP_WM16(_mask, _val) \
+ ({ \
+ typeof(_val) __val = _val; \
+ typeof(_mask) __mask = _mask; \
+ __BF_FIELD_CHECK(__mask, ((u16)0U), __val, \
+ "HWORD_UPDATE: "); \
+ (((typeof(__mask))(__val) << __bf_shf(__mask)) & (__mask)) | \
+ ((__mask) << 16); \
+ })
+
+/**
+ * FIELD_PREP_WM16_CONST() - prepare a constant bitfield element with a mask in
+ * the upper half
+ * @_mask: shifted mask defining the field's length and position
+ * @_val: value to put in the field
+ *
+ * FIELD_PREP_WM16_CONST() masks and shifts up the value, as well as bitwise ORs
+ * the result with the mask shifted up by 16.
+ *
+ * This is useful for a common design of hardware registers where the upper
+ * 16-bit half of a 32-bit register is used as a write-enable mask. In such a
+ * register, a bit in the lower half is only updated if the corresponding bit
+ * in the upper half is high.
+ *
+ * Unlike FIELD_PREP_WM16(), this is a constant expression and can therefore
+ * be used in initializers. Error checking is less comfortable for this
+ * version.
+ */
+#define FIELD_PREP_WM16_CONST(_mask, _val) \
+ ( \
+ FIELD_PREP_CONST(_mask, _val) | \
+ (BUILD_BUG_ON_ZERO(const_true((u64)(_mask) > U16_MAX)) + \
+ ((_mask) << 16)) \
+ )
+
+
+#endif /* _LINUX_HW_BITFIELD_H */
--
2.50.0
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