Re: [PATCH 8/8] cpufreq: elanfreq: Drop support for AMD Elan SC4*

[Zhongqiu Han <zhongqiu.han@oss.qualcomm.com>]

On 5/6/2026 10:42 PM, Sean Young wrote:
> Since commit 8b793a92d862 ("x86/cpu: Remove M486/M486SX/ELAN support"),
> the AMD Elan SC4* is no longer supported, so the cpu frequency
> driver is no longer needed.
> 
> Signed-off-by: Sean Young <sean@mess.org>
> ---
>   drivers/cpufreq/Kconfig.x86 |  15 ---
>   drivers/cpufreq/Makefile    |   1 -
>   drivers/cpufreq/elanfreq.c  | 226 ------------------------------------
>   3 files changed, 242 deletions(-)
>   delete mode 100644 drivers/cpufreq/elanfreq.c
> 

Thanks Sean,

One minor nit: now that the elanfreq driver and its setup code are
removed, should the corresponding elanfreq= entry in
Documentation/admin-guide/kernel-parameters.txt be dropped as well?

https://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm.git/tree/Documentation/admin-guide/kernel-parameters.txt?h=linux-next#n1671


> diff --git a/drivers/cpufreq/Kconfig.x86 b/drivers/cpufreq/Kconfig.x86
> index 865b290b01ff..c42dd39e0b2a 100644
> --- a/drivers/cpufreq/Kconfig.x86
> +++ b/drivers/cpufreq/Kconfig.x86
> @@ -126,21 +126,6 @@ config X86_ACPI_CPUFREQ_CPB
>   	  By enabling this option the acpi_cpufreq driver provides the old
>   	  entry in addition to the new boost ones, for compatibility reasons.
>   
> -config ELAN_CPUFREQ
> -	tristate "AMD Elan SC400 and SC410"
> -	depends on MELAN
> -	help
> -	  This adds the CPUFreq driver for AMD Elan SC400 and SC410
> -	  processors.
> -
> -	  You need to specify the processor maximum speed as boot
> -	  parameter: elanfreq=maxspeed (in kHz) or as module
> -	  parameter "max_freq".
> -
> -	  For details, take a look at <file:Documentation/cpu-freq/>.
> -
> -	  If in doubt, say N.
> -
>   config X86_POWERNOW_K6
>   	tristate "AMD Mobile K6-2/K6-3 PowerNow!"
>   	depends on X86_32
> diff --git a/drivers/cpufreq/Makefile b/drivers/cpufreq/Makefile
> index 96196edf79d5..6c7a39b7f8d2 100644
> --- a/drivers/cpufreq/Makefile
> +++ b/drivers/cpufreq/Makefile
> @@ -40,7 +40,6 @@ obj-$(CONFIG_X86_POWERNOW_K6)		+= powernow-k6.o
>   obj-$(CONFIG_X86_POWERNOW_K7)		+= powernow-k7.o
>   obj-$(CONFIG_X86_LONGHAUL)		+= longhaul.o
>   obj-$(CONFIG_X86_E_POWERSAVER)		+= e_powersaver.o
> -obj-$(CONFIG_ELAN_CPUFREQ)		+= elanfreq.o
>   obj-$(CONFIG_X86_LONGRUN)		+= longrun.o
>   obj-$(CONFIG_X86_GX_SUSPMOD)		+= gx-suspmod.o
>   obj-$(CONFIG_X86_SPEEDSTEP_ICH)		+= speedstep-ich.o
> diff --git a/drivers/cpufreq/elanfreq.c b/drivers/cpufreq/elanfreq.c
> deleted file mode 100644
> index fc5a58088b35..000000000000
> --- a/drivers/cpufreq/elanfreq.c
> +++ /dev/null
> @@ -1,226 +0,0 @@
> -// SPDX-License-Identifier: GPL-2.0-or-later
> -/*
> - *	elanfreq:	cpufreq driver for the AMD ELAN family
> - *
> - *	(c) Copyright 2002 Robert Schwebel <r.schwebel@pengutronix.de>
> - *
> - *	Parts of this code are (c) Sven Geggus <sven@geggus.net>
> - *
> - *      All Rights Reserved.
> - *
> - *	2002-02-13: - initial revision for 2.4.18-pre9 by Robert Schwebel
> - */
> -
> -#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
> -
> -#include <linux/kernel.h>
> -#include <linux/module.h>
> -#include <linux/init.h>
> -
> -#include <linux/delay.h>
> -#include <linux/cpufreq.h>
> -
> -#include <asm/cpu_device_id.h>
> -#include <linux/timex.h>
> -#include <linux/io.h>
> -
> -#define REG_CSCIR 0x22		/* Chip Setup and Control Index Register    */
> -#define REG_CSCDR 0x23		/* Chip Setup and Control Data  Register    */
> -
> -/* Module parameter */
> -static int max_freq;
> -
> -struct s_elan_multiplier {
> -	int clock;		/* frequency in kHz                         */
> -	int val40h;		/* PMU Force Mode register                  */
> -	int val80h;		/* CPU Clock Speed Register                 */
> -};
> -
> -/*
> - * It is important that the frequencies
> - * are listed in ascending order here!
> - */
> -static struct s_elan_multiplier elan_multiplier[] = {
> -	{1000,	0x02,	0x18},
> -	{2000,	0x02,	0x10},
> -	{4000,	0x02,	0x08},
> -	{8000,	0x00,	0x00},
> -	{16000,	0x00,	0x02},
> -	{33000,	0x00,	0x04},
> -	{66000,	0x01,	0x04},
> -	{99000,	0x01,	0x05}
> -};
> -
> -static struct cpufreq_frequency_table elanfreq_table[] = {
> -	{0, 0,	1000},
> -	{0, 1,	2000},
> -	{0, 2,	4000},
> -	{0, 3,	8000},
> -	{0, 4,	16000},
> -	{0, 5,	33000},
> -	{0, 6,	66000},
> -	{0, 7,	99000},
> -	{0, 0,	CPUFREQ_TABLE_END},
> -};
> -
> -
> -/**
> - *	elanfreq_get_cpu_frequency: determine current cpu speed
> - *
> - *	Finds out at which frequency the CPU of the Elan SOC runs
> - *	at the moment. Frequencies from 1 to 33 MHz are generated
> - *	the normal way, 66 and 99 MHz are called "Hyperspeed Mode"
> - *	and have the rest of the chip running with 33 MHz.
> - */
> -
> -static unsigned int elanfreq_get_cpu_frequency(unsigned int cpu)
> -{
> -	u8 clockspeed_reg;    /* Clock Speed Register */
> -
> -	local_irq_disable();
> -	outb_p(0x80, REG_CSCIR);
> -	clockspeed_reg = inb_p(REG_CSCDR);
> -	local_irq_enable();
> -
> -	if ((clockspeed_reg & 0xE0) == 0xE0)
> -		return 0;
> -
> -	/* Are we in CPU clock multiplied mode (66/99 MHz)? */
> -	if ((clockspeed_reg & 0xE0) == 0xC0) {
> -		if ((clockspeed_reg & 0x01) == 0)
> -			return 66000;
> -		else
> -			return 99000;
> -	}
> -
> -	/* 33 MHz is not 32 MHz... */
> -	if ((clockspeed_reg & 0xE0) == 0xA0)
> -		return 33000;
> -
> -	return (1<<((clockspeed_reg & 0xE0) >> 5)) * 1000;
> -}
> -
> -
> -static int elanfreq_target(struct cpufreq_policy *policy,
> -			    unsigned int state)
> -{
> -	/*
> -	 * Access to the Elan's internal registers is indexed via
> -	 * 0x22: Chip Setup & Control Register Index Register (CSCI)
> -	 * 0x23: Chip Setup & Control Register Data  Register (CSCD)
> -	 *
> -	 */
> -
> -	/*
> -	 * 0x40 is the Power Management Unit's Force Mode Register.
> -	 * Bit 6 enables Hyperspeed Mode (66/100 MHz core frequency)
> -	 */
> -
> -	local_irq_disable();
> -	outb_p(0x40, REG_CSCIR);		/* Disable hyperspeed mode */
> -	outb_p(0x00, REG_CSCDR);
> -	local_irq_enable();		/* wait till internal pipelines and */
> -	udelay(1000);			/* buffers have cleaned up          */
> -
> -	local_irq_disable();
> -
> -	/* now, set the CPU clock speed register (0x80) */
> -	outb_p(0x80, REG_CSCIR);
> -	outb_p(elan_multiplier[state].val80h, REG_CSCDR);
> -
> -	/* now, the hyperspeed bit in PMU Force Mode Register (0x40) */
> -	outb_p(0x40, REG_CSCIR);
> -	outb_p(elan_multiplier[state].val40h, REG_CSCDR);
> -	udelay(10000);
> -	local_irq_enable();
> -
> -	return 0;
> -}
> -/*
> - *	Module init and exit code
> - */
> -
> -static int elanfreq_cpu_init(struct cpufreq_policy *policy)
> -{
> -	struct cpuinfo_x86 *c = &cpu_data(0);
> -	struct cpufreq_frequency_table *pos;
> -
> -	/* capability check */
> -	if ((c->x86_vendor != X86_VENDOR_AMD) ||
> -	    (c->x86 != 4) || (c->x86_model != 10))
> -		return -ENODEV;
> -
> -	/* max freq */
> -	if (!max_freq)
> -		max_freq = elanfreq_get_cpu_frequency(0);
> -
> -	/* table init */
> -	cpufreq_for_each_entry(pos, elanfreq_table)
> -		if (pos->frequency > max_freq)
> -			pos->frequency = CPUFREQ_ENTRY_INVALID;
> -
> -	policy->freq_table = elanfreq_table;
> -	return 0;
> -}
> -
> -
> -#ifndef MODULE
> -/**
> - * elanfreq_setup - elanfreq command line parameter parsing
> - *
> - * elanfreq command line parameter.  Use:
> - *  elanfreq=66000
> - * to set the maximum CPU frequency to 66 MHz. Note that in
> - * case you do not give this boot parameter, the maximum
> - * frequency will fall back to _current_ CPU frequency which
> - * might be lower. If you build this as a module, use the
> - * max_freq module parameter instead.
> - */
> -static int __init elanfreq_setup(char *str)
> -{
> -	max_freq = simple_strtoul(str, &str, 0);
> -	pr_warn("You're using the deprecated elanfreq command line option. Use elanfreq.max_freq instead, please!\n");
> -	return 1;
> -}
> -__setup("elanfreq=", elanfreq_setup);
> -#endif
> -
> -
> -static struct cpufreq_driver elanfreq_driver = {
> -	.get		= elanfreq_get_cpu_frequency,
> -	.flags		= CPUFREQ_NO_AUTO_DYNAMIC_SWITCHING,
> -	.verify		= cpufreq_generic_frequency_table_verify,
> -	.target_index	= elanfreq_target,
> -	.init		= elanfreq_cpu_init,
> -	.name		= "elanfreq",
> -};
> -
> -static const struct x86_cpu_id elan_id[] = {
> -	X86_MATCH_VENDOR_FAM_MODEL(AMD, 4, 10, NULL),
> -	{}
> -};
> -MODULE_DEVICE_TABLE(x86cpu, elan_id);
> -
> -static int __init elanfreq_init(void)
> -{
> -	if (!x86_match_cpu(elan_id))
> -		return -ENODEV;
> -	return cpufreq_register_driver(&elanfreq_driver);
> -}
> -
> -
> -static void __exit elanfreq_exit(void)
> -{
> -	cpufreq_unregister_driver(&elanfreq_driver);
> -}
> -
> -
> -module_param(max_freq, int, 0444);
> -
> -MODULE_LICENSE("GPL");
> -MODULE_AUTHOR("Robert Schwebel <r.schwebel@pengutronix.de>, "
> -		"Sven Geggus <sven@geggus.net>");
> -MODULE_DESCRIPTION("cpufreq driver for AMD's Elan CPUs");
> -
> -module_init(elanfreq_init);
> -module_exit(elanfreq_exit);


-- 
Thx and BRs,
Zhongqiu Han