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

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Date:	Wed, 22 Apr 2009 10:55:23 +0800
From:	"Han, Weidong" <weidong.han@...el.com>
To:	"Siddha, Suresh B" <suresh.b.siddha@...el.com>,
	Ingo Molnar <mingo@...e.hu>
CC:	"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()

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.

Regards,
Weidong

> thanks,
> suresh

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