linux-kernel - Re: [PATCH] m68k: disable SRAM at startup

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Message-ID: <20240905065847.GA5215@frolo.corp.macq.eu>
Date: Thu, 5 Sep 2024 08:58:47 +0200
From: Philippe De Muyter <philippe.demuyter@...q.eu>
To: Jean-Michel Hautbois <jeanmichel.hautbois@...eli.org>
Cc: Greg Ungerer <gerg@...ux-m68k.org>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	linux-m68k@...ts.linux-m68k.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] m68k: disable SRAM at startup

Hello Jean-Michel and Greg,

Please add "coldfire' in the title and the explanation of this patch.

Best regards

Philippe

On Wed, Sep 04, 2024 at 04:26:14PM +0200, Jean-Michel Hautbois wrote:
> Some of the internal SoC registers have a higher priority over the MMU
> virtual mappings. The SRAM bank is one of them. If the bootloader
> enables the internal SRAM at address 0x80000000, virtual memory access
> at this address will not hit the MMU - so no TLB data misses would
> occurr.
> 
> Since 0x80000000 is the virtual start address of all applications that
> bit of memory is getting stomped over with inconsistent code and data
> access.
> 
> Fix it by disabling the internal SRAM at startup.
> 
> Signed-off-by: Greg Ungerer <gerg@...ux-m68k.org>
> Tested-by: Jean-Michel Hautbois <jeanmichel.hautbois@...eli.org>
> Signed-off-by: Jean-Michel Hautbois <jeanmichel.hautbois@...eli.org>
> ---
>  arch/m68k/coldfire/head.S | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/arch/m68k/coldfire/head.S b/arch/m68k/coldfire/head.S
> index c6d7fd28c6023..3901a49c47c89 100644
> --- a/arch/m68k/coldfire/head.S
> +++ b/arch/m68k/coldfire/head.S
> @@ -207,6 +207,10 @@ _start:
>  	movec	%d0,%CACR
>  	nop
>  
> +	movel   #0,%d0
> +	movec   %d0,%rambar
> +	nop
> +
>  #ifdef CONFIG_MMU
>  	/*
>  	 *	Identity mapping for the kernel region.
> 
> ---
> base-commit: 431c1646e1f86b949fa3685efc50b660a364c2b6
> change-id: 20240904-fix-cf-virt-mem-sram-abadb27fff2f
> 
> Best regards,
> -- 
> Jean-Michel Hautbois <jeanmichel.hautbois@...eli.org>
>