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

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Message-ID: <b61ef2e3-e573-4867-af5d-fd5fabece4b1@arm.com>
Date:   Thu, 9 Dec 2021 11:13:55 +0000
From:   James Clark <james.clark@....com>
To:     Suzuki K Poulose <suzuki.poulose@....com>,
        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,
        Mathieu Poirier <mathieu.poirier@...aro.org>
Subject: Re: [PATCH 2/3] coresight: Fail to open with return stacks if they
 are unavailable



On 09/12/2021 11:00, Suzuki K Poulose wrote:
> 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 ?
> 
I started changing them all because I had trouble searching for bits by name but then
I thought it would snowball into a bigger change so I undid it.

I think I'll just go and do it now if it's an issue here.

> Otherwise, looks good to me
> 
> Suzuki