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Subject: Re: [PATCH v4 09/10] powerpc/watchpoint: Return available watchpoints
 dynamically
To:     Michael Ellerman <mpe@ellerman.id.au>
Cc:     Jordan Niethe <jniethe5@gmail.com>, mikey@neuling.org,
        apopple@linux.ibm.com, Paul Mackerras <paulus@samba.org>,
        Nicholas Piggin <npiggin@gmail.com>,
        Christophe Leroy <christophe.leroy@c-s.fr>,
        naveen.n.rao@linux.vnet.ibm.com, peterz@infradead.org,
        jolsa@kernel.org, oleg@redhat.com, fweisbec@gmail.com,
        mingo@kernel.org, pedromfc@br.ibm.com, miltonm@us.ibm.com,
        linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org,
        Ravi Bangoria <ravi.bangoria@linux.ibm.com>
References: <20200717040958.70561-1-ravi.bangoria@linux.ibm.com>
 <20200717040958.70561-10-ravi.bangoria@linux.ibm.com>
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 <ccfcf488-0ec9-1737-8368-a848de1d72d1@linux.ibm.com>
 <87k0yxrtex.fsf@mpe.ellerman.id.au>
From:   Ravi Bangoria <ravi.bangoria@linux.ibm.com>
Message-ID: <d3e9bcc9-d73e-6726-edb5-cfdb771b1d61@linux.ibm.com>
Date:   Tue, 21 Jul 2020 19:03:04 +0530
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On 7/21/20 5:06 PM, Michael Ellerman wrote:
> Ravi Bangoria <ravi.bangoria@linux.ibm.com> writes:
>> On 7/20/20 9:12 AM, Jordan Niethe wrote:
>>> On Fri, Jul 17, 2020 at 2:11 PM Ravi Bangoria
>>> <ravi.bangoria@linux.ibm.com> wrote:
>>>>
>>>> So far Book3S Powerpc supported only one watchpoint. Power10 is
>>>> introducing 2nd DAWR. Enable 2nd DAWR support for Power10.
>>>> Availability of 2nd DAWR will depend on CPU_FTR_DAWR1.
>>>>
>>>> Signed-off-by: Ravi Bangoria <ravi.bangoria@linux.ibm.com>
>>>> ---
>>>>    arch/powerpc/include/asm/cputable.h      | 4 +++-
>>>>    arch/powerpc/include/asm/hw_breakpoint.h | 5 +++--
>>>>    2 files changed, 6 insertions(+), 3 deletions(-)
>>>>
>>>> diff --git a/arch/powerpc/include/asm/cputable.h b/arch/powerpc/include/asm/cputable.h
>>>> index 3445c86e1f6f..36a0851a7a9b 100644
>>>> --- a/arch/powerpc/include/asm/cputable.h
>>>> +++ b/arch/powerpc/include/asm/cputable.h
>>>> @@ -633,7 +633,9 @@ enum {
>>>>     * Maximum number of hw breakpoint supported on powerpc. Number of
>>>>     * breakpoints supported by actual hw might be less than this.
>>>>     */
>>>> -#define HBP_NUM_MAX    1
>>>> +#define HBP_NUM_MAX    2
>>>> +#define HBP_NUM_ONE    1
>>>> +#define HBP_NUM_TWO    2
> 
>>> I wonder if these defines are necessary - has it any advantage over
>>> just using the literal?
>>
>> No, not really. Initially I had something like:
>>
>> #define HBP_NUM_MAX    2
>> #define HBP_NUM_P8_P9  1
>> #define HBP_NUM_P10    2
>>
>> But then I thought it's also not right. So I made it _ONE and _TWO.
>> Now the function that decides nr watchpoints dynamically (nr_wp_slots)
>> is in different file, I thought to keep it like this so it would be
>> easier to figure out why _MAX is 2.
> 
> I don't think it makes anything clearer.
> 
> I had to stare at it thinking there was some sort of mapping or
> indirection going on, before I realised it's just literally the number
> of breakpoints.
> 
> So please just do:
> 
> static inline int nr_wp_slots(void)
> {
>         return cpu_has_feature(CPU_FTR_DAWR1) ? 2 : 1;
> }
> 
> If you think HBP_NUM_MAX needs explanation then do that with a comment,
> it can refer to nr_wp_slots() if that's helpful.

Agreed. By adding a comment, we can remove those macros. Will change it.

Thanks,
Ravi