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

[Suzuki K Poulose]

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@xxxxxxx>
> > > > ---
> > > >    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