linux-kernel - Re: [PATCH v2 03/16] powerpc/watchpoint: Introduce function to get nr watchpoints dynamically

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Message-ID: <7851b702-8a93-11a8-6553-e0a51967dfc0@c-s.fr>
Date:   Wed, 1 Apr 2020 08:29:06 +0200
From:   Christophe Leroy <christophe.leroy@....fr>
To:     Ravi Bangoria <ravi.bangoria@...ux.ibm.com>, mpe@...erman.id.au,
        mikey@...ling.org
Cc:     apopple@...ux.ibm.com, paulus@...ba.org, npiggin@...il.com,
        naveen.n.rao@...ux.vnet.ibm.com, peterz@...radead.org,
        jolsa@...nel.org, oleg@...hat.com, fweisbec@...il.com,
        mingo@...nel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 03/16] powerpc/watchpoint: Introduce function to get nr
 watchpoints dynamically



Le 01/04/2020 à 08:12, Ravi Bangoria a écrit :
> So far we had only one watchpoint, so we have hardcoded HBP_NUM to 1.
> But future Power architecture is introducing 2nd DAWR and thus kernel
> should be able to dynamically find actual number of watchpoints
> supported by hw it's running on. Introduce function for the same.
> Also convert HBP_NUM macro to HBP_NUM_MAX, which will now represent
> maximum number of watchpoints supported by Powerpc.


Everywhere else in the code, it is called 'breakpoint', not 'watchpoint'.

Wouldn't it be more consistent to call the function nr_bp_slots() 
instead of nr_wp_slots() ?

Especially as we are likely going to extend your changes to support 
DABR2 in addition to DABR on BOOK3S/32.

Christophe

> 
> Signed-off-by: Ravi Bangoria <ravi.bangoria@...ux.ibm.com>
> ---
>   arch/powerpc/include/asm/cputable.h      | 6 +++++-
>   arch/powerpc/include/asm/hw_breakpoint.h | 5 +++++
>   arch/powerpc/include/asm/processor.h     | 2 +-
>   arch/powerpc/kernel/hw_breakpoint.c      | 2 +-
>   4 files changed, 12 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/powerpc/include/asm/cputable.h b/arch/powerpc/include/asm/cputable.h
> index 40a4d3c6fd99..c67b94f3334c 100644
> --- a/arch/powerpc/include/asm/cputable.h
> +++ b/arch/powerpc/include/asm/cputable.h
> @@ -614,7 +614,11 @@ enum {
>   };
>   #endif /* __powerpc64__ */
>   
> -#define HBP_NUM 1
> +/*
> + * 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
>   
>   #endif /* !__ASSEMBLY__ */
>   
> diff --git a/arch/powerpc/include/asm/hw_breakpoint.h b/arch/powerpc/include/asm/hw_breakpoint.h
> index f2f8d8aa8e3b..518b41eef924 100644
> --- a/arch/powerpc/include/asm/hw_breakpoint.h
> +++ b/arch/powerpc/include/asm/hw_breakpoint.h
> @@ -43,6 +43,11 @@ struct arch_hw_breakpoint {
>   #define DABR_MAX_LEN	8
>   #define DAWR_MAX_LEN	512
>   
> +static inline int nr_wp_slots(void)
> +{
> +	return HBP_NUM_MAX;
> +}
> +
>   #ifdef CONFIG_HAVE_HW_BREAKPOINT
>   #include <linux/kdebug.h>
>   #include <asm/reg.h>
> diff --git a/arch/powerpc/include/asm/processor.h b/arch/powerpc/include/asm/processor.h
> index eedcbfb9a6ff..90f6dbc7ff00 100644
> --- a/arch/powerpc/include/asm/processor.h
> +++ b/arch/powerpc/include/asm/processor.h
> @@ -180,7 +180,7 @@ struct thread_struct {
>   	int		fpexc_mode;	/* floating-point exception mode */
>   	unsigned int	align_ctl;	/* alignment handling control */
>   #ifdef CONFIG_HAVE_HW_BREAKPOINT
> -	struct perf_event *ptrace_bps[HBP_NUM];
> +	struct perf_event *ptrace_bps[HBP_NUM_MAX];
>   	/*
>   	 * Helps identify source of single-step exception and subsequent
>   	 * hw-breakpoint enablement
> diff --git a/arch/powerpc/kernel/hw_breakpoint.c b/arch/powerpc/kernel/hw_breakpoint.c
> index 72f461bd70fb..4120349e2abe 100644
> --- a/arch/powerpc/kernel/hw_breakpoint.c
> +++ b/arch/powerpc/kernel/hw_breakpoint.c
> @@ -38,7 +38,7 @@ static DEFINE_PER_CPU(struct perf_event *, bp_per_reg);
>   int hw_breakpoint_slots(int type)
>   {
>   	if (type == TYPE_DATA)
> -		return HBP_NUM;
> +		return nr_wp_slots();
>   	return 0;		/* no instruction breakpoints available */
>   }
>   
>