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

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Date:	Wed, 4 Mar 2015 06:31:06 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	"Li, Aubrey" <aubrey.li@...ux.intel.com>
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


* 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.

Thanks,

	Ingo
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