linux-kernel - Re: [PATCH v2] MIPS: Make check condition for SDBBP consistent with EJTAG spec

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Message-ID: <20210209121124.GA11134@alpha.franken.de>
Date:   Tue, 9 Feb 2021 13:11:24 +0100
From:   Thomas Bogendoerfer <tsbogend@...ha.franken.de>
To:     Tiezhu Yang <yangtiezhu@...ngson.cn>
Cc:     linux-mips@...r.kernel.org, linux-kernel@...r.kernel.org,
        Xuefeng Li <lixuefeng@...ngson.cn>
Subject: Re: [PATCH v2] MIPS: Make check condition for SDBBP consistent with
 EJTAG spec

On Tue, Feb 09, 2021 at 01:05:25PM +0800, Tiezhu Yang wrote:
> According to MIPS EJTAG Specification [1], a Debug Breakpoint
> exception occurs when an SDBBP instruction is executed, the
> CP0_DEBUG bit DBp indicates that a Debug Breakpoint exception
> occurred, just check bit DBp for SDBBP is more accurate.
> 
> [1] http://www.t-es-t.hu/download/mips/md00047f.pdf
> 
> Signed-off-by: Tiezhu Yang <yangtiezhu@...ngson.cn>
> ---
> 
> v2: add MIPS_DEBUG_DBP definition
> 
>  arch/mips/include/asm/mipsregs.h | 4 ++++
>  arch/mips/kernel/genex.S         | 4 ++--
>  2 files changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/mips/include/asm/mipsregs.h b/arch/mips/include/asm/mipsregs.h
> index a0e8ae5..9c8099a 100644
> --- a/arch/mips/include/asm/mipsregs.h
> +++ b/arch/mips/include/asm/mipsregs.h
> @@ -1085,6 +1085,10 @@
>  #define CVMVMCONF_RMMUSIZEM1_S	0
>  #define CVMVMCONF_RMMUSIZEM1	(_U64CAST_(0xff) << CVMVMCONF_RMMUSIZEM1_S)
>  
> +/* Debug register field definitions */
> +#define MIPS_DEBUG_DBP_SHIFT	1
> +#define MIPS_DEBUG_DBP		(_ULCAST_(1) << MIPS_DEBUG_DBP_SHIFT)
> +
>  /*
>   * Coprocessor 1 (FPU) register names
>   */
> diff --git a/arch/mips/kernel/genex.S b/arch/mips/kernel/genex.S
> index bcce32a..743d759 100644
> --- a/arch/mips/kernel/genex.S
> +++ b/arch/mips/kernel/genex.S
> @@ -349,8 +349,8 @@ NESTED(ejtag_debug_handler, PT_SIZE, sp)
>  	MTC0	k0, CP0_DESAVE
>  	mfc0	k0, CP0_DEBUG
>  
> -	sll	k0, k0, 30	# Check for SDBBP.
> -	bgez	k0, ejtag_return
> +	andi	k0, k0, MIPS_DEBUG_DBP	# Check for SDBBP.
> +	beqz	k0, ejtag_return

IMHO both implementations are doing the same thing.

Thomas.

-- 
Crap can work. Given enough thrust pigs will fly, but it's not necessarily a
good idea.                                                [ RFC1925, 2.3 ]