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

[Ravi Bangoria]

On 7/21/20 5:06 PM, Michael Ellerman wrote:
> Ravi Bangoria <ravi.bangoria@xxxxxxxxxxxxx> writes:
> > On 7/20/20 9:12 AM, Jordan Niethe wrote:
> > > On Fri, Jul 17, 2020 at 2:11 PM Ravi Bangoria
> > > <ravi.bangoria@xxxxxxxxxxxxx> 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@xxxxxxxxxxxxx>
> > > > ---
> > > >    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