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

Ravi Bangoria
2020-07-21T13:33:48Z

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