linux-kernel - Re: [PATCH] x86: Bypass legacy PIC and PIT on ACPI hardware reduced platform

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Date:	Wed, 04 Mar 2015 14:04:59 +0800
From:	"Li, Aubrey" <aubrey.li@...ux.intel.com>
To:	Ingo Molnar <mingo@...nel.org>
CC:	"alan@...ux.intel.com" <alan@...ux.intel.com>,
	"H. Peter Anvin" <hpa@...ux.intel.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, arjan@...ux.intel.com,
	"Rafael J. Wysocki" <rjw@...ysocki.net>, Len.Brown@...el.com,
	x86@...nel.org, LKML <linux-kernel@...r.kernel.org>,
	Borislav Petkov <bp@...en8.de>
Subject: Re: [PATCH] x86: Bypass legacy PIC and PIT on ACPI hardware reduced
 platform

On 2015/3/4 13:31, Ingo Molnar wrote:
> 
> * Li, Aubrey <aubrey.li@...ux.intel.com> wrote:
> 
>> On 2015/3/4 13:08, Ingo Molnar wrote:
>>>
>>> * Li, Aubrey <aubrey.li@...ux.intel.com> wrote:
>>>
>>>> On ACPI hardware reduced platform, the legacy PIC and PIT may not be
>>>> initialized even though they may be present in silicon. Touching
>>>> these legacy components causes unexpected result on system.
>>>>
>>>> On Bay Trail-T(ASUS-T100) platform, touching these legacy components
>>>> blocks platform hardware low idle power state(S0ix) during system suspend.
>>>> So we should bypass them on ACPI hardware reduced platform.
>>>>
>>>> Suggested-by: Arjan van de Ven <arjan@...ux.intel.com>
>>>> Signed-off-by: Li Aubrey <aubrey.li@...ux.intel.com>
>>>> Cc: Len Brown <len.brown@...el.com>
>>>> Cc: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
>>>> ---
>>>>  arch/x86/kernel/irqinit.c | 6 +++++-
>>>>  arch/x86/kernel/time.c    | 3 ++-
>>>>  2 files changed, 7 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/arch/x86/kernel/irqinit.c b/arch/x86/kernel/irqinit.c
>>>> index 70e181e..9a64cc3 100644
>>>> --- a/arch/x86/kernel/irqinit.c
>>>> +++ b/arch/x86/kernel/irqinit.c
>>>> @@ -75,7 +75,11 @@ void __init init_ISA_irqs(void)
>>>>  #if defined(CONFIG_X86_64) || defined(CONFIG_X86_LOCAL_APIC)
>>>>  	init_bsp_APIC();
>>>>  #endif
>>>> -	legacy_pic->init(0);
>>>> +	if (acpi_gbl_reduced_hardware) {
>>>> +		pr_info("Using NULL legacy PIC\n");
>>>> +		legacy_pic = &null_legacy_pic;
>>>> +	} else
>>>> +		legacy_pic->init(0);
>>>>  
>>>>  	for (i = 0; i < nr_legacy_irqs(); i++)
>>>>  		irq_set_chip_and_handler(i, chip, handle_level_irq);
>>>> diff --git a/arch/x86/kernel/time.c b/arch/x86/kernel/time.c
>>>> index 25adc0e..5ba94fa 100644
>>>> --- a/arch/x86/kernel/time.c
>>>> +++ b/arch/x86/kernel/time.c
>>>> @@ -14,6 +14,7 @@
>>>>  #include <linux/i8253.h>
>>>>  #include <linux/time.h>
>>>>  #include <linux/export.h>
>>>> +#include <linux/acpi.h>
>>>>  
>>>>  #include <asm/vsyscall.h>
>>>>  #include <asm/x86_init.h>
>>>> @@ -76,7 +77,7 @@ void __init setup_default_timer_irq(void)
>>>>  /* Default timer init function */
>>>>  void __init hpet_time_init(void)
>>>>  {
>>>> -	if (!hpet_enable())
>>>> +	if (!hpet_enable() && !acpi_gbl_reduced_hardware)
>>>>  		setup_pit_timer();
>>>>  	setup_default_timer_irq();
>>>>  }
>>>
>>> So the whole acpi_gbl_reduced_hardware flaggery sucks as it mixes 
>>> various hardware drivers that have little relation to each other...
>>>
>>> Instead of having a proper platform init this flag hooks into various 
>>> drivers and generic code, such as the efi reboot and shutdown code, 
>>> and now the generic irq init code.
>>>
>>> For this IRQ init problem, why not add a proper callback to 
>>> x86_platform_ops, define your own IRQ init function, initialize it in 
>>> your platform init sequence and let it be called? That solves it 
>>> without creating an ugly mix of different platform methods.
>>>
>>> For the EFI shutdown case, what's wrong with setting your own 
>>> pm_power_off handler like most of the other platforms are doing? Plus 
>>> the EFI code in drivers/firmware/efi/reboot.c should probably only set 
>>> the shutdown handler if pm_power_off is still NULL.
>>
>> I think our goal is to make the code as generic as possible for all 
>> x86 platform, rather than creating a new x86 branch, I added Alan 
>> Cox for this strategy discussion.
>>
>> Do you have any inputs for the patch itself?
> 
> Other than that the patch is unacceptable for an upstream merge in its 
> current form for the reason I mentioned? No.

So you are suggesting we extend a new x86 platform branch and override
the x86_platform and pm_power_off and reboot, like what intel_mid does?

Thanks,
-Aubrey

> 
> Thanks,
> 
> 	Ingo
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