linux-kernel - Re: [PATCH 03/15] powerpc/watchpoint: Introduce function to get nr watchpoints dynamically

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Message-ID: <53b8bf54-200f-6f37-5870-e641b35f373c@c-s.fr>
Date:   Tue, 17 Mar 2020 11:21:39 +0100
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 03/15] powerpc/watchpoint: Introduce function to get nr
 watchpoints dynamically



Le 09/03/2020 à 09:57, 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.
> 
> Signed-off-by: Ravi Bangoria <ravi.bangoria@...ux.ibm.com>
> ---
>   arch/powerpc/include/asm/cputable.h      | 6 +++++-
>   arch/powerpc/include/asm/hw_breakpoint.h | 2 ++
>   arch/powerpc/include/asm/processor.h     | 2 +-
>   arch/powerpc/kernel/hw_breakpoint.c      | 2 +-
>   arch/powerpc/kernel/process.c            | 6 ++++++
>   5 files changed, 15 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..741c4f7573c4 100644
> --- a/arch/powerpc/include/asm/hw_breakpoint.h
> +++ b/arch/powerpc/include/asm/hw_breakpoint.h
> @@ -43,6 +43,8 @@ struct arch_hw_breakpoint {
>   #define DABR_MAX_LEN	8
>   #define DAWR_MAX_LEN	512
>   
> +extern int nr_wp_slots(void);

'extern' keyword is unneeded and irrelevant here. Please remove it. Even 
checkpatch is unhappy 
(https://openpower.xyz/job/snowpatch/job/snowpatch-linux-checkpatch/12172//artifact/linux/checkpatch.log)


> +
>   #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 8387698bd5b6..666b2825278c 100644
> --- a/arch/powerpc/include/asm/processor.h
> +++ b/arch/powerpc/include/asm/processor.h
> @@ -176,7 +176,7 @@ 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 d0854320bb50..e68798cee3fa 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 */
>   }
>   
> diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
> index 110db94cdf3c..6d4b029532e2 100644
> --- a/arch/powerpc/kernel/process.c
> +++ b/arch/powerpc/kernel/process.c
> @@ -835,6 +835,12 @@ static inline bool hw_brk_match(struct arch_hw_breakpoint *a,
>   	return true;
>   }
>   
> +/* Returns total number of data breakpoints available. */
> +int nr_wp_slots(void)
> +{
> +	return HBP_NUM_MAX;
> +}
> +

This is not worth a global function. At least it should be a static 
function located in hw_breakpoint.c. But it would be even better to have 
it as a static inline in asm/hw_breakpoint.h

Christophe