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

[Ravi Bangoria <ravi.bangoria@linux.ibm.com>]

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.

>>
>>   #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@linux.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