linux-kernel - Re: [patch 4/5] x2apic, IR: remove reinit_intr_remapped_IO

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Message-ID: <20090422100335.GH18226@elte.hu>
Date:	Wed, 22 Apr 2009 12:03:35 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	"Han, Weidong" <weidong.han@...el.com>
Cc:	"Siddha, Suresh B" <suresh.b.siddha@...el.com>,
	"hpa@...or.com" <hpa@...or.com>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"dwmw2@...radead.org" <dwmw2@...radead.org>
Subject: Re: [patch 4/5] x2apic, IR: remove reinit_intr_remapped_IO_APIC()


* Han, Weidong <weidong.han@...el.com> wrote:

> Siddha, Suresh B wrote:
> > On Tue, 2009-04-21 at 00:01 -0700, Ingo Molnar wrote:
> >> * Han, Weidong <weidong.han@...el.com> wrote:
> >> 
> >>> Siddha, Suresh B wrote:
> >>>> When interrupt-remapping is enabled, We are relying on
> >>>> setup_IO_APIC_irqs() to configure remapped entries in the IO-APIC,
> >>>> which comes little bit later after enabling interrupt-remapping.
> >>>> 
> >>>> Meanwhile, Restore of old io-apic entries after enabling
> >>>> interrupt-remapping will not make the interrupts through io-apic
> >>>> functional anyway. 
> >>>> 
> >>>> So remove unnecessary reinit_intr_remapped_IO_APIC().
> >>>> 
> >>>> Signed-off-by: Suresh Siddha <suresh.b.siddha@...el.com>
> >>>> Cc: Weidong Han <weidong.han@...el.com>
> >>>> ---
> >>>> 
> >>>> Index: tip/arch/x86/include/asm/io_apic.h
> >>>> ===================================================================
> >>>> --- tip.orig/arch/x86/include/asm/io_apic.h
> >>>> +++ tip/arch/x86/include/asm/io_apic.h
> >>>> @@ -166,8 +166,6 @@ extern void free_ioapic_entries(struct I
> >>>>  extern int save_IO_APIC_setup(struct IO_APIC_route_entry
> >>>>  **ioapic_entries); extern void mask_IO_APIC_setup(struct
> >>>>  IO_APIC_route_entry **ioapic_entries); extern int
> >>>> restore_IO_APIC_setup(struct IO_APIC_route_entry **ioapic_entries);
> >>>> -extern void reinit_intr_remapped_IO_APIC(int intr_remapping,
> >>>> -	struct IO_APIC_route_entry **ioapic_entries);
> >>>> 
> >>>>  extern void probe_nr_irqs_gsi(void);
> >>>> 
> >>>> Index: tip/arch/x86/kernel/apic/apic.c
> >>>> ===================================================================
> >>>> --- tip.orig/arch/x86/kernel/apic/apic.c
> >>>> +++ tip/arch/x86/kernel/apic/apic.c
> >>>> @@ -1416,8 +1416,6 @@ end_restore:
> >>>>  		 * IR enabling failed
> >>>>  		 */
> >>>>  		restore_IO_APIC_setup(ioapic_entries);
> >>>> -	else
> >>>> -		reinit_intr_remapped_IO_APIC(x2apic_preenabled, ioapic_entries);
> >>> 
> >>> Whether IR enabling succeeds or fails, it always needs to restore
> >>> old IOAPIC entries. Due to removing reinit_intr_remapped_IO_APIC
> >>> here, it needs to also remove the "if (ret)" before
> >>> restore_IO_APIC_setup(ioapic_entries);
> >> 
> >> Ok - i skipped this patch for now.
> > 
> > Let me clarify what I am doing in this patch:
> > 
> > When interrupt-remapping is enabled, IO-APIC entries need to be setup
> > in the re-mappable format (pointing to interrupt-remapping table
> > entries setup by the OS). This remapping configuration is happening
> > in the same place where we traditionally configure IO-APIC (i.e., in
> > setup_IO_APIC_irqs()).
> > 
> > So when we enable interrupt-remapping successfully, there is no need
> > to restore old io-apic RTE entries before we actually do a complete
> > configuration shortly in setup_IO_APIC_irqs(). Old IO-APIC RTE's may
> > be in traditional format (non re-mappable) or in re-mappable format
> > pointing to interrupt-remapping table entries setup by BIOS. Restoring
> > both of these will not make IO-APIC functional. We have to rely on
> > setup_IO_APIC_irqs() for proper configuration by OS.
> > 
> > So I am removing this unnecessary and broken step.
> > 
> > When enabling interrupt-remapping is not successful, we are doing
> > plain restore of old RTE's (which will still work as we went back to
> > original no-remapping state). Complete IO-APIC configuration will be
> > done shortly in setup_IO_APIC_irqs().
> > 
> 
> Clear explanation. I misunderstood it. This patch is fine.

Applied to tip:x86/apic - thanks guys,

	Ingo
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