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

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Date:   Tue, 9 Feb 2021 15:00:18 +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 09:09:52PM +0800, Tiezhu Yang wrote:
> On 02/09/2021 08:11 PM, Thomas Bogendoerfer wrote:
> > 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.
> 
> When I read the original code, it looks a little confusing
> at first glance, the initial aim of this patch is to make the code
> more readable and easier to understand.

which your version is, but the description sounds like there is a semantic
change somewhere (at least to me). So with a little bit rewording I'm
fine with applying your patch.

Thomas.

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