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

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Message-ID: <f6e2378a-11be-0886-6105-86ad9ccbc992@arm.com>
Date:   Wed, 12 Jan 2022 09:46:38 +0000
From:   Suzuki K Poulose <suzuki.poulose@....com>
To:     James Clark <james.clark@....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 07/01/2022 15:10, James Clark wrote:
> 
> 
> On 09/12/2021 11:13, James Clark wrote:
>>
>>
>> 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.
> 
> Hi Suzuki,
> 
> I started on this and I think the only worthwhile change is to make them all consistent
> with sysreg.h. As in have xxx_SHIFT and xxx_MASK style definitions like:
> 
>    #define TRCCONFIGR_INSTP0_SHIFT		1
>    #define TRCCONFIGR_INSTPO_MASK		GENMASK(1,0)
> 
> This has been done for SPE and some of the new ETM stuff. If that sounds right to you
> I will go and do it as a followup patch to this one. It is quite a bit change so I can
> see maybe we don't want to do it? (Personally I would vote to do it)

Yes, please go ahead with that. Thanks for taking it up !

Suzuki