linux-kernel - Re: [PATCH] x86: APIC: Remove apic_write

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Date:	Fri, 18 Jul 2008 12:52:59 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	"Maciej W. Rozycki" <macro@...ux-mips.org>
Cc:	x86@...nel.org, linux-kernel@...r.kernel.org,
	Suresh Siddha <suresh.b.siddha@...el.com>,
	Yinghai Lu <yhlu.kernel@...il.com>,
	Jeremy Fitzhardinge <jeremy@...p.org>
Subject: Re: [PATCH] x86: APIC: Remove apic_write_around(); use alternatives


* Maciej W. Rozycki <macro@...ux-mips.org> wrote:

>  Use alternatives to select the workaround for the 11AP Pentium 
> erratum for the affected steppings on the fly rather than build time.  
> Remove the X86_GOOD_APIC configuration option and replace all the 
> calls to apic_write_around() with plain apic_write(), protecting 
> accesses to the ESR as appropriate due to the 3AP Pentium erratum.  
> Remove apic_read_around() and all its invocations altogether as not 
> needed.  Remove apic_write_atomic() and all its implementing backends.  
> The use of ASM_OUTPUT2() is not strictly needed for input constraints, 
> but I have used it for readability's sake.

wow, impressive patch!

>  I had the feeling no one else was brave enough to do it, so I went 
> ahead and here it is.  Verified by checking the generated assembly and 
> tested with both a 32-bit and a 64-bit configuration, also with the 
> 11AP "feature" forced on and verified with gdb on /proc/kcore to work 
> as expected (as an 11AP machines are quite hard to get hands on these 
> days).  Some script complained about the use of "volatile", but 
> apic_write() needs it for the same reason and is effectively a 
> replacement for writel(), so I have disregarded it.

kudos for pulling this off :-)

applied to tip/x86/apic. This will interact with tip/x86/x2apic but that 
topic is being worked on anyway. The interaction should be trivial.

	Ingo
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