[PATCH v2] powerpc: Enable generic cpu idle-loop

[PATCH v2] powerpc: Enable generic cpu idle-loop

[Vaibhav Jain]

This minor patch enables config option GENERIC_IDLE_POLL_SETUP for arch
powerpc. This should add support for kernel param 'nohlt'.

Powerpc kernel also supports another kernel boot-time param called
'powersave' which can also be used to disable all cpu idle-states and
forces CPU to an idle-loop similar to what cpu_idle_poll() does. Hence this
patch  also updates the handling of 'powersave=off' kernel param to enable
generic cpu idle-loop if its enabled.

Signed-off-by: Vaibhav Jain<vaibhav@linux.ibm.com>
---
Changelog:

Since v1:
https://lore.kernel.org/all/20230818050739.827851-1-vaibhav@linux.ibm.com
* Updated powersave_off() to enable generic cpu idle-loop if
'powersave=off' kernel arg is given. [Mpe]
* Update patch description
---
 Documentation/admin-guide/kernel-parameters.txt | 2 +-
 arch/powerpc/Kconfig                            | 1 +
 arch/powerpc/kernel/idle.c                      | 3 +++
 3 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 722b6eca2e93..6b657ebafcfb 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -3738,7 +3738,7 @@
 
 	nohibernate	[HIBERNATION] Disable hibernation and resume.
 
-	nohlt		[ARM,ARM64,MICROBLAZE,MIPS,SH] Forces the kernel to
+	nohlt		[ARM,ARM64,MICROBLAZE,MIPS,PPC,SH] Forces the kernel to
 			busy wait in do_idle() and not use the arch_cpu_idle()
 			implementation; requires CONFIG_GENERIC_IDLE_POLL_SETUP
 			to be effective. This is useful on platforms where the
diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 0b1172cbeccb..574661403800 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -193,6 +193,7 @@ config PPC
 	select GENERIC_CPU_VULNERABILITIES	if PPC_BARRIER_NOSPEC
 	select GENERIC_EARLY_IOREMAP
 	select GENERIC_GETTIMEOFDAY
+	select GENERIC_IDLE_POLL_SETUP
 	select GENERIC_IRQ_SHOW
 	select GENERIC_IRQ_SHOW_LEVEL
 	select GENERIC_PCI_IOMAP		if PCI
diff --git a/arch/powerpc/kernel/idle.c b/arch/powerpc/kernel/idle.c
index b1c0418b25c8..7367a0698459 100644
--- a/arch/powerpc/kernel/idle.c
+++ b/arch/powerpc/kernel/idle.c
@@ -21,6 +21,7 @@
 #include <linux/cpu.h>
 #include <linux/sysctl.h>
 #include <linux/tick.h>
+#include <linux/cpu.h>
 
 #include <asm/processor.h>
 #include <asm/cputable.h>
@@ -35,6 +36,8 @@ EXPORT_SYMBOL(cpuidle_disable);
 
 static int __init powersave_off(char *arg)
 {
+	/* Use generic idle loop if thats available */
+	cpu_idle_poll_ctrl(true);
 	ppc_md.power_save = NULL;
 	cpuidle_disable = IDLE_POWERSAVE_OFF;
 	return 1;
-- 
2.41.0

Re: [PATCH v2] powerpc: Enable generic cpu idle-loop

[Michael Ellerman]

Hi Vaibhav,

Vaibhav Jain <vaibhav@linux.ibm.com> writes:
> This minor patch enables config option GENERIC_IDLE_POLL_SETUP for arch
> powerpc. This should add support for kernel param 'nohlt'.
>
> Powerpc kernel also supports another kernel boot-time param called
> 'powersave' which can also be used to disable all cpu idle-states and
> forces CPU to an idle-loop similar to what cpu_idle_poll() does. Hence this
> patch  also updates the handling of 'powersave=off' kernel param to enable
> generic cpu idle-loop if its enabled.
>
> Signed-off-by: Vaibhav Jain<vaibhav@linux.ibm.com>
> ---
> Changelog:
>
> Since v1:
> https://lore.kernel.org/all/20230818050739.827851-1-vaibhav@linux.ibm.com
> * Updated powersave_off() to enable generic cpu idle-loop if
> 'powersave=off' kernel arg is given. [Mpe]
> * Update patch description

I had already merged the v1 when I saw this, and ...

> diff --git a/arch/powerpc/kernel/idle.c b/arch/powerpc/kernel/idle.c
> index b1c0418b25c8..7367a0698459 100644
> --- a/arch/powerpc/kernel/idle.c
> +++ b/arch/powerpc/kernel/idle.c
> @@ -35,6 +36,8 @@ EXPORT_SYMBOL(cpuidle_disable);
>  
>  static int __init powersave_off(char *arg)
>  {
> +	/* Use generic idle loop if thats available */
> +	cpu_idle_poll_ctrl(true);
>  	ppc_md.power_save = NULL;
>  	cpuidle_disable = IDLE_POWERSAVE_OFF;
>  	return 1;

The hope here would be that we could remove the need for cpuidle_disable.

cheers