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

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Message-ID: <alpine.DEB.2.21.2102161506160.1521@angie.orcam.me.uk>
Date:   Tue, 16 Feb 2021 15:07:42 +0100 (CET)
From:   "Maciej W. Rozycki" <macro@...am.me.uk>
To:     Thomas Bogendoerfer <tsbogend@...ha.franken.de>
cc:     Tiezhu Yang <yangtiezhu@...ngson.cn>, 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, 9 Feb 2021, Thomas Bogendoerfer wrote:

> > > > 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.

 Why is it confusing?  This is assembly and you're supposed to understand 
this stuff when looking into it.  Don't fix what ain't broke!

  Maciej