linux-kernel - Re: [v3][PATCH 8/8] book3e/kexec/kdump: recover "r4 = 0" to create the initial TLB

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Date:	Tue, 17 Dec 2013 21:50:38 -0600
From:	Scott Wood <scottwood@...escale.com>
To:	Tiejun Chen <tiejun.chen@...driver.com>
CC:	<benh@...nel.crashing.org>, <linuxppc-dev@...ts.ozlabs.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [v3][PATCH 8/8] book3e/kexec/kdump: recover "r4 = 0" to create
 the initial TLB

On Tue, 2013-07-09 at 16:03 +0800, Tiejun Chen wrote:
> In commit 96f013f, "powerpc/kexec: Add kexec "hold" support for Book3e
> processors", requires that GPR4 survive the "hold" process, for IBM Blue
> Gene/Q with with some very strange firmware. But for FSL Book3E, r4 = 1
> to indicate that the initial TLB entry for this core already exists so
> we still should set r4 with 0 to create that initial TLB.
> 
> Signed-off-by: Tiejun Chen <tiejun.chen@...driver.com>
> ---
>  arch/powerpc/kernel/head_64.S |    4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/arch/powerpc/kernel/head_64.S b/arch/powerpc/kernel/head_64.S
> index 0b46c9d..d546c5e 100644
> --- a/arch/powerpc/kernel/head_64.S
> +++ b/arch/powerpc/kernel/head_64.S
> @@ -127,6 +127,10 @@ __secondary_hold:
>  	/* Grab our physical cpu number */
>  	mr	r24,r3
>  	/* stash r4 for book3e */
> +#ifdef CONFIG_PPC_FSL_BOOK3E
> +	/* we need to setup initial TLB entry. */
> +	li	r4,0
> +#endif
>  	mr	r25,r4

This breaks being able to build one kernel that supports both FSL book3e
and IBM book3e.

-Scott


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