Re: [PATCH 3/9] arm: add call to CPU idle quirks handler

Paul Osmialowski
2015-06-26T05:34:07Z

Hi Nicolas,

Thanks for your proposal, however, I have some trouble with it.

That would look lovely:

#include <linux/linkage.h>
#include <asm/assembler.h>

/*
* cpu_kinetis_do_idle()
*
* Idle the processor (wait for interrupt).
*
* IRQs are already disabled.
*/
ENTRY(cpu_kinetis_do_idle)
wfi
movw r3, #:lower16:0xe0082000
movt r3, #:upper16:0xe0082000
ldr r0, [r3, #0]
orr r2, r0, #0x85000000
str r2, [r3, #0]
ret lr
ENDPROC(cpu_kinetis_do_idle)

But... what about the rest of this hypothetical proc_kinetis.S file?

It would be a lot of code duplication with proc-v7m.S I think.

I could define CPU_KINETIS as such:

config CPU_KINETIS
bool
select CPU_V7M

But there's no such thing like customize_processor_functions that would be
called after proc-v7m.S define_processor_functions specified things like
idle routine.

Finally, while I was searching for suitable arm_pm_idle-based solution, I
found idle.c in mach-gemini that encouraged me to write my own idle.c for
Kinetis:

/*
* arch/arm/mach-kinetis/idle.c
*/

#include <linux/init.h>
#include <linux/io.h>
#include <asm/system_misc.h>
#include <asm/proc-fns.h>

static void kinetis_idle(void)
{
asm volatile ("wfi");

/*
* This is a dirty hack that invalidates the I/D bus cache
* on Kinetis K70. This must be done after idle.
*/
writel(readl(IOMEM(0xe0082000)) | 0x85000000, IOMEM(0xe0082000));
}

static int __init kinetis_idle_init(void)
{
arm_pm_idle = kinetis_idle;
return 0;
}

arch_initcall(kinetis_idle_init);

Et voila:

(gdb) c
Continuing.
^C
Program received signal SIGTRAP, Trace/breakpoint trap.
kinetis_idle () at ../arch/arm/mach-kinetis/idle.c:18
18 writel(readl(IOMEM(0xe0082000)) | 0x85000000,
IOMEM(0xe0082000));
(gdb) bt
#0 kinetis_idle () at ../arch/arm/mach-kinetis/idle.c:18
#1 0x0800a91e in arch_cpu_idle () at ../arch/arm/kernel/process.c:70
#2 0x08025402 in cpuidle_idle_call (state=<value optimized out>)
at ../kernel/sched/idle.c:157
#3 cpu_idle_loop (state=<value optimized out>) at
../kernel/sched/idle.c:253
#4 cpu_startup_entry (state=<value optimized out>) at
../kernel/sched/idle.c:301
#5 0x081bf816 in start_kernel () at ../init/main.c:683
#6 0x08008024 in stext () at ../arch/arm/kernel/head-nommu.S:85
(gdb)

On Thu, 25 Jun 2015, Nicolas Pitre wrote:

> On Tue, 23 Jun 2015, Arnd Bergmann wrote:
>
>> On Tuesday 23 June 2015 23:19:41 Paul Osmialowski wrote:
>>> Some SoCs need additional actions to be performed after arch idle,
>>> e.g. Kinetis requires invalidation of the I/D bus cache.
>>>
>>> Such handler could be held in provided <mach/idle.h> header file.
>>>
>>> Signed-off-by: Paul Osmialowski <pawelo@king.net.pl>
>>> ---
>>> arch/arm/Kconfig | 7 +++++++
>>> arch/arm/kernel/process.c | 7 +++++++
>>> 2 files changed, 14 insertions(+)
>>>
>>> diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
>>> index 8e3a833..8ef8f8f 100644
>>> --- a/arch/arm/Kconfig
>>> +++ b/arch/arm/Kconfig
>>> @@ -98,6 +98,13 @@ config ARM_HAS_SG_CHAIN
>>> config NEED_SG_DMA_LENGTH
>>> bool
>>>
>>> +config NEED_MACH_IDLE_H
>>> + bool
>>> +
>>> +config ARM_CPU_IDLE_QUIRKS
>>> + bool
>>> + select NEED_MACH_IDLE_H
>>> +
>>
>> We're not adding header files like this, please come up
>> with another solution. How about a cpuidle driver, or
>> possibly just overriding arm_pm_idle()?
>
> If the WFI instruction always requires I and D flushing, then it might
> be a better idea to provide a replacement for the corresponding
> cpu_*_do_idle function. Plenty of examples exist for other cpu_*
> functions.
>
>
> Nicolas
>