linux-kernel - Re: FW: 2.6.38.3 and 2.6.39-rc4 hangs after "Booting the kernel" on quad Pentium Pro system

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Date:	Sat, 23 Apr 2011 10:51:08 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Thomas Meyer <thomas@...3r.de>
CC:	Yuhong Bao <yuhongbao_386@...mail.com>, chris@...muel.org,
	alan@...rguk.ukuu.org.uk, tglx@...utronix.de, mingo@...hat.com,
	x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: FW: 2.6.38.3 and 2.6.39-rc4 hangs after "Booting the kernel"
 on quad Pentium Pro system

On 04/23/2011 06:52 AM, Thomas Meyer wrote:
>
> so your bios seems to report the size in AX/BX. the code in
> arch/x86/boot/memory.c move the return sizes from CX/DX into AX/BX, when
> CX or DX is not zero.
>
> Could you try to change the line:
>
> 	} else if (oreg.ax == 15*1024) {
> 		boot_params.alt_mem_k = (oreg.dx<<  6) + oreg.ax;
>
> to
> 	} else if (oreg.ax == 15*1024) {
> 		boot_params.alt_mem_k = (oreg.bx<<  6) + oreg.ax;
>
> That should fix your misdetection.
>
> The assembler code in arch/i386/boot/setup.S seemed to move AX/BX into
> CX/DX, when CX and(!) DX were zero. Then used CX/DX to calc the memory
> size.
>
> PS: gitk --follow arch/x86/boot/memory.c seems to react strangley...
>

Ah yes, this should have been bx; ax/bx and cx/dx forms pairs (unlike 
the normal x86 convention of DX:AX and BX:CX forming pairs), and it 
doesn't make sense to mix and match them.

	-hpa
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