linux-kernel - Re: [PULL -tip] x86: replacing mp_config_X with mpc

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Date:	Wed, 14 Jan 2009 12:01:42 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Jaswinder Singh Rajput <jaswinderlinux@...il.com>
Cc:	Jaswinder Singh Rajput <jaswinder@...radead.org>,
	"Maciej W. Rozycki" <macro@...ux-mips.org>,
	Alexey Starikovskiy <astarikovskiy@...e.de>,
	Yinghai Lu <yinghai@...nel.org>, paul.s.diefenbaugh@...el.com,
	jun.nakajima@...el.com, Alan Cox <alan@...rguk.ukuu.org.uk>,
	x86 maintainers <x86@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PULL -tip] x86: replacing mp_config_X with mpc_X


* Jaswinder Singh Rajput <jaswinderlinux@...il.com> wrote:

> On Mon, Jan 12, 2009 at 6:41 PM, Ingo Molnar <mingo@...e.hu> wrote:
> >
> > * Jaswinder Singh Rajput <jaswinder@...radead.org> wrote:
> >
> >> -struct mp_config_ioapic {
> >> -     unsigned long mp_apicaddr;
> >> -     unsigned int mp_apicid;
> >> -     unsigned char mp_type;
> >> -     unsigned char mp_apicver;
> >> -     unsigned char mp_flags;
> >> -};
> >> -
> >> -struct mp_config_intsrc {
> >> -     unsigned int mp_dstapic;
> >> -     unsigned char mp_type;
> >> -     unsigned char mp_irqtype;
> >> -     unsigned short mp_irqflag;
> >> -     unsigned char mp_srcbus;
> >> -     unsigned char mp_srcbusirq;
> >> -     unsigned char mp_dstirq;
> >> -};
> >
> > So you replaced that with mpc_ioapic and mpc_intsrc uses:
> >
> >  struct mpc_ioapic {
> >         unsigned char type;
> >         unsigned char apicid;
> >         unsigned char apicver;
> >         unsigned char flags;
> >         unsigned int apicaddr;
> >  };
> >
> >  struct mpc_intsrc {
> >         unsigned char type;
> >         unsigned char irqtype;
> >         unsigned short irqflag;
> >         unsigned char srcbus;
> >         unsigned char srcbusirq;
> >         unsigned char dstapic;
> >         unsigned char dstirq;
> >  };
> >
> > And removed the mp_config_ioapic and mp_config_intsrc types.
> >
> > The mp_config_ioapic and mp_config_intsrc types are kernel-internal, while
> > mpc_ioapic and mpc_intsrc is an MP Specification type - the lowlevel
> > structure of these tables as provided in RAM or ROM by the BIOS.
> >
> > Here's the potential problems that need to be thought through:
> >
> > - the biggest potential problem is that apicaddr is 32-bit wide while
> >  mp_apicaddr is 64-bit wide, on the 64-bit kernel. Can an apic address be
> >  above 4 GB, in an mptable? I dont think it can be.
> >
> 
> mp_apicaddr is getting its value from apicaddr which is u32
> (arch/x86/kernel/acpi/boot.c)
>  OR
> mp_apicaddr is getting its value from apicaddr which is u32
> (arch/x86/kernel/mpparse.c)
> 
> > - another problem could be that dstapic are all 1-byte entities - while in
> >  the in-kernel version (mp_apicid and mp_dstapic) they are 32 bit. The
> >  ACPI code fills in the tables too so maybe there it can be wider than 8
> >  bits?
> >
> 
> mp_apicid is getting its value from uniq_ioapic_id(id) which returns
> u8 (arch/x86/kernel/acpi/boot.c)
>  OR
> mp_apicid is getting its value from reg_00.bits.ID which also 8 bits
> (arch/x86/kernel/io_apic.c)
>  OR
> mp_apicid is getting its value from apicid which also 8 bits
> (arch/x86/kernel/mpparse.c)
> 
> and
> 
> mp_dstapic is getting its value from mp_apicid which is already 8 bits
> (arch/x86/kernel/acpi/boot.c)
>  OR
> mp_dstapic is getting its value from mpc_intsrc->dstapic which is
> already 8 bits (arch/x86/kernel/mpparse.c)
> 
> By using current structure we are wasting space as well as creating
> confusion for checking u8 <-> u32 and u32 <-> u64.

ok, that sounds fair enough - double-checking that we are not introducing 
some stupid limit somewhere was important.

I've pulled your two cleanup commits, thanks,

	Ingo
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