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Message-ID: <f2b879d3e8120c7aeb0e6c9a5fd45b15a2b8e5a0.camel@gmail.com>
Date: Fri, 17 Oct 2025 13:33:19 +0100
From: Nuno Sá <noname.nuno@...il.com>
To: Geert Uytterhoeven <geert+renesas@...der.be>, Michael Turquette
<mturquette@...libre.com>, Stephen Boyd <sboyd@...nel.org>, Nicolas Ferre
<nicolas.ferre@...rochip.com>, Alexandre Belloni
<alexandre.belloni@...tlin.com>, Claudiu Beznea
<claudiu.beznea@...on.dev>, Giovanni Cabiddu <giovanni.cabiddu@...el.com>,
Herbert Xu <herbert@...dor.apana.org.au>, David Miller
<davem@...emloft.net>, Linus Walleij <linus.walleij@...aro.org>, Bartosz
Golaszewski <brgl@...ev.pl>, Joel Stanley <joel@....id.au>, Andrew Jeffery
<andrew@...econstruct.com.au>, Crt Mori <cmo@...exis.com>, Jonathan
Cameron <jic23@...nel.org>, Lars-Peter Clausen <lars@...afoo.de>, Jacky
Huang <ychuang3@...oton.com>, Shan-Chun Hung <schung@...oton.com>, Yury
Norov <yury.norov@...il.com>, Rasmus Villemoes <linux@...musvillemoes.dk>,
Jaroslav Kysela <perex@...ex.cz>, Takashi Iwai <tiwai@...e.com>, Johannes
Berg <johannes@...solutions.net>, Jakub Kicinski <kuba@...nel.org>, Alex
Elder <elder@...e.org>, David Laight <david.laight.linux@...il.com>,
Vincent Mailhol <mailhol.vincent@...adoo.fr>, Jason Baron
<jbaron@...mai.com>, Borislav Petkov <bp@...en8.de>, Tony Luck
<tony.luck@...el.com>, Michael Hennerich <Michael.Hennerich@...log.com>,
Kim Seer Paller <kimseer.paller@...log.com>, David Lechner
<dlechner@...libre.com>, Nuno Sá <nuno.sa@...log.com>,
Andy Shevchenko <andy@...nel.org>, Richard Genoud
<richard.genoud@...tlin.com>, Cosmin Tanislav <demonsingur@...il.com>,
Biju Das <biju.das.jz@...renesas.com>, Jianping Shen
<Jianping.Shen@...bosch.com>
Cc: linux-clk@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
linux-renesas-soc@...r.kernel.org, linux-crypto@...r.kernel.org,
linux-edac@...r.kernel.org, qat-linux@...el.com,
linux-gpio@...r.kernel.org, linux-aspeed@...ts.ozlabs.org,
linux-iio@...r.kernel.org, linux-sound@...r.kernel.org,
linux-kernel@...r.kernel.org, Jonathan Cameron
<Jonathan.Cameron@...wei.com>
Subject: Re: [PATCH v4 2/4] bitfield: Add non-constant field_{prep,get}()
helpers
On Fri, 2025-10-17 at 12:54 +0200, Geert Uytterhoeven wrote:
> The existing FIELD_{GET,PREP}() macros are limited to compile-time
> constants. However, it is very common to prepare or extract bitfield
> elements where the bitfield mask is not a compile-time constant.
>
> To avoid this limitation, the AT91 clock driver and several other
> drivers already have their own non-const field_{prep,get}() macros.
> Make them available for general use by consolidating them in
> <linux/bitfield.h>, and improve them slightly:
> 1. Avoid evaluating macro parameters more than once,
> 2. Replace "ffs() - 1" by "__ffs()",
> 3. Support 64-bit use on 32-bit architectures.
>
> This is deliberately not merged into the existing FIELD_{GET,PREP}()
> macros, as people expressed the desire to keep stricter variants for
> increased safety, or for performance critical paths.
>
> Signed-off-by: Geert Uytterhoeven <geert+renesas@...der.be>
> Acked-by: Alexandre Belloni <alexandre.belloni@...tlin.com>
> Acked-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>
> Acked-by: Crt Mori <cmo@...exis.com>
> ---
Hopefully this gets merged soon. About time to have these variants (I do have a
driver submitted - in review - which is adding yet another variant of this)
Acked-by: Nuno Sá <nuno.sa@...log.com>
> v4:
> - Add Acked-by,
> - Rebase on top of commit 7c68005a46108ffa ("crypto: qat - relocate
> power management debugfs helper APIs") in v6.17-rc1,
> - Convert more recently introduced upstream copies:
> - drivers/edac/ie31200_edac.c
> - drivers/iio/dac/ad3530r.c
>
> v3:
> - Add Acked-by,
> - Drop underscores from macro parameters,
> - Use __auto_type where possible,
> - Correctly cast reg to the mask type,
> - Introduces __val and __reg intermediates to simplify the actual
> operation,
> - Drop unneeded parentheses,
> - Clarify having both FIELD_{GET,PREP}() and field_{get,prep}(),
>
> v2:
> - Cast val resp. reg to the mask type,
> - Fix 64-bit use on 32-bit architectures,
> - Convert new upstream users:
> - drivers/crypto/intel/qat/qat_common/adf_gen4_pm_debugfs.c
> - drivers/gpio/gpio-aspeed.c
> - drivers/iio/temperature/mlx90614.c
> - drivers/pinctrl/nuvoton/pinctrl-ma35.c
> - sound/usb/mixer_quirks.c
> - Convert new user queued in renesas-devel for v6.15:
> - drivers/soc/renesas/rz-sysc.c
> ---
> drivers/clk/at91/clk-peripheral.c | 1 +
> drivers/clk/at91/pmc.h | 3 --
> .../intel/qat/qat_common/adf_pm_dbgfs_utils.c | 8 +----
> drivers/edac/ie31200_edac.c | 4 +--
> drivers/gpio/gpio-aspeed.c | 5 +--
> drivers/iio/dac/ad3530r.c | 3 --
> drivers/iio/temperature/mlx90614.c | 5 +--
> drivers/pinctrl/nuvoton/pinctrl-ma35.c | 4 ---
> drivers/soc/renesas/rz-sysc.c | 3 +-
> include/linux/bitfield.h | 36 +++++++++++++++++++
> sound/usb/mixer_quirks.c | 4 ---
> 11 files changed, 42 insertions(+), 34 deletions(-)
>
> diff --git a/drivers/clk/at91/clk-peripheral.c b/drivers/clk/at91/clk-
> peripheral.c
> index e700f40fd87f9327..e7208c47268b6397 100644
> --- a/drivers/clk/at91/clk-peripheral.c
> +++ b/drivers/clk/at91/clk-peripheral.c
> @@ -3,6 +3,7 @@
> * Copyright (C) 2013 Boris BREZILLON <b.brezillon@...rkiz.com>
> */
>
> +#include <linux/bitfield.h>
> #include <linux/bitops.h>
> #include <linux/clk-provider.h>
> #include <linux/clkdev.h>
> diff --git a/drivers/clk/at91/pmc.h b/drivers/clk/at91/pmc.h
> index 5daa32c4cf2540d7..543d7aee8d248cdb 100644
> --- a/drivers/clk/at91/pmc.h
> +++ b/drivers/clk/at91/pmc.h
> @@ -117,9 +117,6 @@ struct at91_clk_pms {
> unsigned int parent;
> };
>
> -#define field_get(_mask, _reg) (((_reg) & (_mask)) >> (ffs(_mask) - 1))
> -#define field_prep(_mask, _val) (((_val) << (ffs(_mask) - 1)) & (_mask))
> -
> #define ndck(a, s) (a[s - 1].id + 1)
> #define nck(a) (a[ARRAY_SIZE(a) - 1].id + 1)
>
> diff --git a/drivers/crypto/intel/qat/qat_common/adf_pm_dbgfs_utils.c
> b/drivers/crypto/intel/qat/qat_common/adf_pm_dbgfs_utils.c
> index 69295a9ddf0ac92f..4ccc94ed9493a64c 100644
> --- a/drivers/crypto/intel/qat/qat_common/adf_pm_dbgfs_utils.c
> +++ b/drivers/crypto/intel/qat/qat_common/adf_pm_dbgfs_utils.c
> @@ -1,18 +1,12 @@
> // SPDX-License-Identifier: GPL-2.0-only
> /* Copyright(c) 2025 Intel Corporation */
> +#include <linux/bitfield.h>
> #include <linux/bitops.h>
> #include <linux/sprintf.h>
> #include <linux/string_helpers.h>
>
> #include "adf_pm_dbgfs_utils.h"
>
> -/*
> - * This is needed because a variable is used to index the mask at
> - * pm_scnprint_table(), making it not compile time constant, so the compile
> - * asserts from FIELD_GET() or u32_get_bits() won't be fulfilled.
> - */
> -#define field_get(_mask, _reg) (((_reg) & (_mask)) >> (ffs(_mask) - 1))
> -
> #define PM_INFO_MAX_KEY_LEN 21
>
> static int pm_scnprint_table(char *buff, const struct pm_status_row *table,
> diff --git a/drivers/edac/ie31200_edac.c b/drivers/edac/ie31200_edac.c
> index 5a080ab65476dacf..dfc9a9cecd74207d 100644
> --- a/drivers/edac/ie31200_edac.c
> +++ b/drivers/edac/ie31200_edac.c
> @@ -44,6 +44,7 @@
> * but lo_hi_readq() ensures that we are safe across all e3-1200 processors.
> */
>
> +#include <linux/bitfield.h>
> #include <linux/module.h>
> #include <linux/init.h>
> #include <linux/pci.h>
> @@ -139,9 +140,6 @@
> #define IE31200_CAPID0_DDPCD BIT(6)
> #define IE31200_CAPID0_ECC BIT(1)
>
> -/* Non-constant mask variant of FIELD_GET() */
> -#define field_get(_mask, _reg) (((_reg) & (_mask)) >> (ffs(_mask) - 1))
> -
> static int nr_channels;
> static struct pci_dev *mci_pdev;
> static int ie31200_registered = 1;
> diff --git a/drivers/gpio/gpio-aspeed.c b/drivers/gpio/gpio-aspeed.c
> index 7953a9c4e36d7550..3da999334971d501 100644
> --- a/drivers/gpio/gpio-aspeed.c
> +++ b/drivers/gpio/gpio-aspeed.c
> @@ -5,6 +5,7 @@
> * Joel Stanley <joel@....id.au>
> */
>
> +#include <linux/bitfield.h>
> #include <linux/cleanup.h>
> #include <linux/clk.h>
> #include <linux/gpio/aspeed.h>
> @@ -31,10 +32,6 @@
> #include <linux/gpio/consumer.h>
> #include "gpiolib.h"
>
> -/* Non-constant mask variant of FIELD_GET() and FIELD_PREP() */
> -#define field_get(_mask, _reg) (((_reg) & (_mask)) >> (ffs(_mask) - 1))
> -#define field_prep(_mask, _val) (((_val) << (ffs(_mask) - 1)) &
> (_mask))
> -
> #define GPIO_G7_IRQ_STS_BASE 0x100
> #define GPIO_G7_IRQ_STS_OFFSET(x) (GPIO_G7_IRQ_STS_BASE + (x) * 0x4)
> #define GPIO_G7_CTRL_REG_BASE 0x180
> diff --git a/drivers/iio/dac/ad3530r.c b/drivers/iio/dac/ad3530r.c
> index 6134613777b8e1d4..b97b46090d808ee7 100644
> --- a/drivers/iio/dac/ad3530r.c
> +++ b/drivers/iio/dac/ad3530r.c
> @@ -53,9 +53,6 @@
> #define AD3530R_MAX_CHANNELS 8
> #define AD3531R_MAX_CHANNELS 4
>
> -/* Non-constant mask variant of FIELD_PREP() */
> -#define field_prep(_mask, _val) (((_val) << (ffs(_mask) - 1)) &
> (_mask))
> -
> enum ad3530r_mode {
> AD3530R_NORMAL_OP,
> AD3530R_POWERDOWN_1K,
> diff --git a/drivers/iio/temperature/mlx90614.c
> b/drivers/iio/temperature/mlx90614.c
> index 8a44a00bfd5ece38..1ad21b73e1b44cb0 100644
> --- a/drivers/iio/temperature/mlx90614.c
> +++ b/drivers/iio/temperature/mlx90614.c
> @@ -22,6 +22,7 @@
> * the "wakeup" GPIO is not given, power management will be disabled.
> */
>
> +#include <linux/bitfield.h>
> #include <linux/delay.h>
> #include <linux/err.h>
> #include <linux/gpio/consumer.h>
> @@ -68,10 +69,6 @@
> #define MLX90614_CONST_SCALE 20 /* Scale in milliKelvin (0.02 * 1000) */
> #define MLX90614_CONST_FIR 0x7 /* Fixed value for FIR part of low pass filter
> */
>
> -/* Non-constant mask variant of FIELD_GET() and FIELD_PREP() */
> -#define field_get(_mask, _reg) (((_reg) & (_mask)) >> (ffs(_mask) - 1))
> -#define field_prep(_mask, _val) (((_val) << (ffs(_mask) - 1)) &
> (_mask))
> -
> struct mlx_chip_info {
> /* EEPROM offsets with 16-bit data, MSB first */
> /* emissivity correction coefficient */
> diff --git a/drivers/pinctrl/nuvoton/pinctrl-ma35.c
> b/drivers/pinctrl/nuvoton/pinctrl-ma35.c
> index cdad01d68a37e365..8d71dc53cc1de1f8 100644
> --- a/drivers/pinctrl/nuvoton/pinctrl-ma35.c
> +++ b/drivers/pinctrl/nuvoton/pinctrl-ma35.c
> @@ -81,10 +81,6 @@
> #define MVOLT_1800 0
> #define MVOLT_3300 1
>
> -/* Non-constant mask variant of FIELD_GET() and FIELD_PREP() */
> -#define field_get(_mask, _reg) (((_reg) & (_mask)) >> (ffs(_mask) - 1))
> -#define field_prep(_mask, _val) (((_val) << (ffs(_mask) - 1)) &
> (_mask))
> -
> static const char * const gpio_group_name[] = {
> "gpioa", "gpiob", "gpioc", "gpiod", "gpioe", "gpiof", "gpiog",
> "gpioh", "gpioi", "gpioj", "gpiok", "gpiol", "gpiom", "gpion",
> diff --git a/drivers/soc/renesas/rz-sysc.c b/drivers/soc/renesas/rz-sysc.c
> index 9f79e299e6f41641..73eaf8b9d69f7208 100644
> --- a/drivers/soc/renesas/rz-sysc.c
> +++ b/drivers/soc/renesas/rz-sysc.c
> @@ -5,6 +5,7 @@
> * Copyright (C) 2024 Renesas Electronics Corp.
> */
>
> +#include <linux/bitfield.h>
> #include <linux/cleanup.h>
> #include <linux/io.h>
> #include <linux/mfd/syscon.h>
> @@ -16,8 +17,6 @@
>
> #include "rz-sysc.h"
>
> -#define field_get(_mask, _reg) (((_reg) & (_mask)) >> (ffs(_mask) - 1))
> -
> /**
> * struct rz_sysc - RZ SYSC private data structure
> * @base: SYSC base address
> diff --git a/include/linux/bitfield.h b/include/linux/bitfield.h
> index 7ff817bdae19b468..c999fe70076f6684 100644
> --- a/include/linux/bitfield.h
> +++ b/include/linux/bitfield.h
> @@ -220,4 +220,40 @@ __MAKE_OP(64)
> #undef __MAKE_OP
> #undef ____MAKE_OP
>
> +/**
> + * field_prep() - prepare a bitfield element
> + * @mask: shifted mask defining the field's length and position
> + * @val: value to put in the field
> + *
> + * field_prep() masks and shifts up the value. The result should be
> + * combined with other fields of the bitfield using logical OR.
> + * Unlike FIELD_PREP(), @mask is not limited to a compile-time constant.
> + */
> +#define field_prep(mask, val) \
> + ({ \
> + __auto_type __mask = (mask); \
> + typeof(mask) __val = (val); \
> + unsigned int __shift = sizeof(mask) <= 4 ? \
> + __ffs(__mask) :
> __ffs64(__mask); \
> + (__val << __shift) & __mask; \
> + })
> +
> +/**
> + * field_get() - extract a bitfield element
> + * @mask: shifted mask defining the field's length and position
> + * @reg: value of entire bitfield
> + *
> + * field_get() extracts the field specified by @mask from the
> + * bitfield passed in as @reg by masking and shifting it down.
> + * Unlike FIELD_GET(), @mask is not limited to a compile-time constant.
> + */
> +#define field_get(mask, reg) \
> + ({ \
> + __auto_type __mask = (mask); \
> + typeof(mask) __reg = (reg); \
> + unsigned int __shift = sizeof(mask) <= 4 ? \
> + __ffs(__mask) :
> __ffs64(__mask); \
> + (__reg & __mask) >> __shift; \
> + })
> +
> #endif
> diff --git a/sound/usb/mixer_quirks.c b/sound/usb/mixer_quirks.c
> index 828af3095b86ee0a..6eee89cbc0867f2b 100644
> --- a/sound/usb/mixer_quirks.c
> +++ b/sound/usb/mixer_quirks.c
> @@ -3311,10 +3311,6 @@ static int snd_bbfpro_controls_create(struct
> usb_mixer_interface *mixer)
> #define RME_DIGIFACE_REGISTER(reg, mask) (((reg) << 16) | (mask))
> #define RME_DIGIFACE_INVERT BIT(31)
>
> -/* Nonconst helpers */
> -#define field_get(_mask, _reg) (((_reg) & (_mask)) >> (ffs(_mask) - 1))
> -#define field_prep(_mask, _val) (((_val) << (ffs(_mask) - 1)) & (_mask))
> -
> static int snd_rme_digiface_write_reg(struct snd_kcontrol *kcontrol, int
> item, u16 mask, u16 val)
> {
> struct usb_mixer_elem_list *list = snd_kcontrol_chip(kcontrol);
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