Subject: Re: [patch 4/5] x2apic, IR: remove reinit_intr_remapped_IO_APIC()
From: Suresh Siddha <suresh.b.siddha@intel.com>
Reply-To: suresh.b.siddha@intel.com
To: Ingo Molnar <mingo@elte.hu>
Cc: "Han, Weidong" <weidong.han@intel.com>, "hpa@zytor.com" <hpa@zytor.com>,
       "tglx@linutronix.de" <tglx@linutronix.de>,
       "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
       "dwmw2@infradead.org" <dwmw2@infradead.org>
In-Reply-To: <20090421070130.GC22937@elte.hu>
References: <20090420200450.128993000@linux-os.sc.intel.com>
	 <20090420200450.552359000@linux-os.sc.intel.com>
	 <715D42877B251141A38726ABF5CABF2C01A6B7F9FC@pdsmsx503.ccr.corp.intel.com>
	 <20090421070130.GC22937@elte.hu>
Content-Type: text/plain
Organization: Intel Corp
Date: Tue, 21 Apr 2009 11:24:44 -0700
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On Tue, 2009-04-21 at 00:01 -0700, Ingo Molnar wrote:
> * Han, Weidong <weidong.han@intel.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@intel.com>
> > > Cc: Weidong Han <weidong.han@intel.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().

thanks,
suresh

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