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

["Li, Aubrey" <aubrey.li@linux.intel.com>]

On 2015/3/4 13:08, Ingo Molnar wrote:
> 
> * Li, Aubrey <aubrey.li@linux.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@linux.intel.com>
>> Signed-off-by: Li Aubrey <aubrey.li@linux.intel.com>
>> Cc: Len Brown <len.brown@intel.com>
>> Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.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?

Thanks,
-Aubrey

> 
> Thanks,
> 
> 	Ingo
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