linux-kernel - Re: [PATCH 2/3] coresight: Fail to open with return stacks if they are unavailable

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Message-ID: <b52ef2f3-9e30-59a6-2aea-e46c93915868@arm.com>
Date:   Thu, 9 Dec 2021 11:00:40 +0000
From:   Suzuki K Poulose <suzuki.poulose@....com>
To:     James Clark <james.clark@....com>, mathieu.poirier@...aro.org,
        coresight@...ts.linaro.org
Cc:     Mike Leach <mike.leach@...aro.org>, Leo Yan <leo.yan@...aro.org>,
        John Garry <john.garry@...wei.com>,
        Will Deacon <will@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-perf-users@...r.kernel.org
Subject: Re: [PATCH 2/3] coresight: Fail to open with return stacks if they
 are unavailable

On 08/12/2021 16:09, James Clark 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@....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 d2bafb50c66a..0a9bb943a5e5 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);
> +		}

nit: While at this, please could you change the hard coded value
to ETM4_CFG_BIT_RETSTK ?

Otherwise, looks good to me

Suzuki