linux-kernel - Re: [PATCH 04/12] powerpc: Implement hw_breakpoint_arch

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Date:   Mon, 28 May 2018 21:31:07 +1000
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Frederic Weisbecker <frederic@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>, Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Joel Fernandes <joel.opensrc@...il.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Chris Zankel <chris@...kel.net>,
        Paul Mackerras <paulus@...ba.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Will Deacon <will.deacon@....com>,
        Rich Felker <dalias@...c.org>, Ingo Molnar <mingo@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Max Filippov <jcmvbkbc@...il.com>
Subject: Re: [PATCH 04/12] powerpc: Implement hw_breakpoint_arch_parse()

Frederic Weisbecker <frederic@...nel.org> writes:

> On Thu, May 24, 2018 at 12:01:52PM +1000, Michael Ellerman wrote:
>> Frederic Weisbecker <frederic@...nel.org> writes:
>> 
>> > diff --git a/arch/powerpc/kernel/hw_breakpoint.c b/arch/powerpc/kernel/hw_breakpoint.c
>> > index 348cac9..fba6527 100644
>> > --- a/arch/powerpc/kernel/hw_breakpoint.c
>> > +++ b/arch/powerpc/kernel/hw_breakpoint.c
>> > @@ -139,30 +139,31 @@ int arch_bp_generic_fields(int type, int *gen_bp_type)
>> >  /*
>> >   * Validate the arch-specific HW Breakpoint register settings
>> >   */
>> > -int arch_validate_hwbkpt_settings(struct perf_event *bp)
>> > +int hw_breakpoint_arch_parse(struct perf_event *bp,
>> > +			     struct perf_event_attr *attr,
>> > +			     struct arch_hw_breakpoint *hw)
>> 
>> I think the semantics here are that we are reading from bp/attr and
>> writing to hw?
>> 
>> If so would some sprinkling of const on the first two parameters help
>> make that clearer?
>
> I seem to remember there was an issue with that due to the various functions
> we call that need to be converted to take const as well. I thought I would
> do it in a seperate series but actually it should be no big deal to do it
> on this one.

Yeah, that does sometimes snowball out of control.

> Let me try that and respin.

Cool. It would be nice to have, but obviously not crucial.

cheers