linux-kernel - Re: [PATCH v4 09/10] powerpc/watchpoint: Return available watchpoints dynamically

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Date:   Tue, 21 Jul 2020 09:27:37 +0530
From:   Ravi Bangoria <ravi.bangoria@...ux.ibm.com>
To:     Jordan Niethe <jniethe5@...il.com>
Cc:     Michael Ellerman <mpe@...erman.id.au>, mikey@...ling.org,
        apopple@...ux.ibm.com, Paul Mackerras <paulus@...ba.org>,
        Nicholas Piggin <npiggin@...il.com>,
        Christophe Leroy <christophe.leroy@....fr>,
        naveen.n.rao@...ux.vnet.ibm.com, peterz@...radead.org,
        jolsa@...nel.org, oleg@...hat.com, fweisbec@...il.com,
        mingo@...nel.org, pedromfc@...ibm.com, miltonm@...ibm.com,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        Ravi Bangoria <ravi.bangoria@...ux.ibm.com>
Subject: Re: [PATCH v4 09/10] powerpc/watchpoint: Return available watchpoints
 dynamically



On 7/20/20 9:12 AM, Jordan Niethe wrote:
> On Fri, Jul 17, 2020 at 2:11 PM Ravi Bangoria
> <ravi.bangoria@...ux.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@...ux.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.

>>
>>   #endif /* !__ASSEMBLY__ */
>>
>> diff --git a/arch/powerpc/include/asm/hw_breakpoint.h b/arch/powerpc/include/asm/hw_breakpoint.h
>> index cb424799da0d..d4eab1694bcd 100644
>> --- a/arch/powerpc/include/asm/hw_breakpoint.h
>> +++ b/arch/powerpc/include/asm/hw_breakpoint.h
>> @@ -5,10 +5,11 @@
>>    * Copyright 2010, IBM Corporation.
>>    * Author: K.Prasad <prasad@...ux.vnet.ibm.com>
>>    */
>> -
> Was removing this line deliberate?

Nah. Will remove that hunk.

>>   #ifndef _PPC_BOOK3S_64_HW_BREAKPOINT_H
>>   #define _PPC_BOOK3S_64_HW_BREAKPOINT_H
>>
>> +#include <asm/cpu_has_feature.h>
>> +
>>   #ifdef __KERNEL__
>>   struct arch_hw_breakpoint {
>>          unsigned long   address;
>> @@ -46,7 +47,7 @@ struct arch_hw_breakpoint {
>>
>>   static inline int nr_wp_slots(void)
>>   {
>> -       return HBP_NUM_MAX;
>> +       return cpu_has_feature(CPU_FTR_DAWR1) ? HBP_NUM_TWO : HBP_NUM_ONE;
> So it'd be something like:
> +       return cpu_has_feature(CPU_FTR_DAWR1) ? HBP_NUM_MAX : 1;
> But thinking that there might be more slots added in the future, it
> may be better to make the number of slots a variable that is set
> during the init and then have this function return that.

Not sure I follow. What do you mean by setting number of slots a
variable that is set during the init?

Thanks,
Ravi