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

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Message-ID: <20211210172220.GA1238770@p14s>
Date:   Fri, 10 Dec 2021 10:22:20 -0700
From:   Mathieu Poirier <mathieu.poirier@...aro.org>
To:     James Clark <james.clark@....com>
Cc:     Suzuki K Poulose <suzuki.poulose@....com>,
        coresight@...ts.linaro.org, 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

Hi James,

On Thu, Dec 09, 2021 at 11:13:55AM +0000, 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.

I can apply this set right away and you send another patch to fix all hard coded
bitfields or you can send another revision with all 4 patches included in it
(bitfields fix plus these 3).  Just let me know what you want to do.  And next
time please add a cover letter.

Thanks,
Mathieu

> 
> > Otherwise, looks good to me
> > 
> > Suzuki