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Message-ID: <c3549740-f01c-4a98-8a3e-5af70326f0eb@bootlin.com>
Date: Fri, 17 Oct 2025 14:43:17 +0200
From: Richard GENOUD <richard.genoud@...tlin.com>
To: Nuno Sá <noname.nuno@...il.com>,
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>,
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
Le 17/10/2025 à 14:33, Nuno Sá a écrit :
> 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>
Same here, I would happily drop field_{get,set} from my series under
review to include bitfield.h
Thanks Geert!
Acked-by: Richard Genoud <richard.genoud@...tlin.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);
--
Richard Genoud, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com
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