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

[Ravi Bangoria]

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.

> >   #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@xxxxxxxxxxxxxxxxxx>
> >    */
> > -
> 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