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From:   Mike Leach <mike.leach@linaro.org>
Date:   Fri, 21 Jan 2022 12:42:34 +0000
Message-ID: <CAJ9a7ViuON11QZRhejcmCM3KOkWx-i0NZw_Kh-2m1Ps0bop2xw@mail.gmail.com>
Subject: Re: [PATCH v2 2/6] coresight: Fail to open with return stacks if they
 are unavailable
To:     James Clark <James.Clark@arm.com>
Cc:     suzuki.poulose@arm.com, mathieu.poirier@linaro.org,
        coresight@lists.linaro.org, leo.yan@linaro.com,
        Leo Yan <leo.yan@linaro.org>,
        John Garry <john.garry@huawei.com>,
        Will Deacon <will@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Jiri Olsa <jolsa@redhat.com>,
        Namhyung Kim <namhyung@kernel.org>,
        linux-arm-kernel@lists.infradead.org, linux-doc@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org
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Reviewed-by: Mike Leach <mike.leach@linaro.org>

On Thu, 13 Jan 2022 at 09:11, James Clark <james.clark@arm.com> wrote:
>
> Maintain consistency with the other options by failing to open when they
> aren't supported. For example ETM_OPT_TS, ETM_OPT_CTXTID2 and the newly
> added ETM_OPT_BRANCH_BROADCAST all return with -EINVAL if they are
> requested but not supported by hardware.
>
> The consequence of not doing this is that the user may not be
> aware that they are not enabling the feature as it is silently disabled.
>
> Signed-off-by: James Clark <james.clark@arm.com>
> ---
>  drivers/hwtracing/coresight/coresight-etm4x-core.c | 13 +++++++++----
>  1 file changed, 9 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/hwtracing/coresight/coresight-etm4x-core.c b/drivers/hwtracing/coresight/coresight-etm4x-core.c
> index 04669ecc0efa..a93c1a5fe045 100644
> --- a/drivers/hwtracing/coresight/coresight-etm4x-core.c
> +++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c
> @@ -674,10 +674,15 @@ static int etm4_parse_event_config(struct coresight_device *csdev,
>         }
>
>         /* return stack - enable if selected and supported */
> -       if ((attr->config & BIT(ETM_OPT_RETSTK)) && drvdata->retstack)
> -               /* bit[12], Return stack enable bit */
> -               config->cfg |= BIT(12);
> -
> +       if (attr->config & BIT(ETM_OPT_RETSTK)) {
> +               if (!drvdata->retstack) {
> +                       ret = -EINVAL;
> +                       goto out;
> +               } else {
> +                       /* bit[12], Return stack enable bit */
> +                       config->cfg |= BIT(12);
> +               }
> +       }
>         /*
>          * Set any selected configuration and preset.
>          *
> --
> 2.28.0
>


-- 
Mike Leach
Principal Engineer, ARM Ltd.
Manchester Design Centre. UK