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

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Date:   Mon, 20 Jul 2020 13:42:42 +1000
From:   Jordan Niethe <jniethe5@...il.com>
To:     Ravi Bangoria <ravi.bangoria@...ux.ibm.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
Subject: Re: [PATCH v4 09/10] powerpc/watchpoint: Return available watchpoints dynamically

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?
>
>  #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?
>  #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.
>  }
>
>  #ifdef CONFIG_HAVE_HW_BREAKPOINT
> --
> 2.26.2
>