Re: [PATCH] coresight: docs: Remove target sink from examples

[James Clark]

On 12/12/2024 7:38 pm, Steve Clevenger wrote:
> On 12/12/2024 7:27 AM, James Clark wrote:
> > On 11/12/2024 6:01 pm, Steve Clevenger wrote:
> > > Hi James,
> > >
> > > I thought I'd mention this issue with multicore self-hosted trace. The
> > > perf command line syntax does not allow a sink "type" to be specified
> > > (e.g. @tmc_etf or @tmc_etr). For multicore, it doesn't make sense to
> > > specify a processor mapped sink as would be the case for single core
> > > trace. A sink "type" should be allowed to avoid the auto select default.
> > > In our case, the default is the ETF sink.
> > >
> > > Thanks,
> > > Steve C.
> >
> > I'm sure it would be possible to add support for this, but I'm wondering
> > if the real issue is that the default selection logic is wrong? Are you
> > saying the default you get is ETF but you want ETR? And there is both
> > for each ETM? The default selection logic isn't easy to summarize but it
> > should prefer ETR (sysmem) over ETF (link sink), see coresight_find_sink().
> >
> > It's probably better to fix that rather than add a new sink selection
> > feature. Maybe if you shared a diagram of your coresight architecture it
> > would help.
> >
> > Thanks
> > James
>
> Hi James,
>
> It appears the default sink selection is ETF for multicore trace. In any
> case, for the Arm® CoreSight Base System Architecture STC Level
> compliance, I need to be able to specify the sink type.

Yep it makes sense to add support for selecting it then then, I will put 
it on the list but not sure about the priority. I think looking into why 
the default isn't working is more important for now.

> The Ampere CoreSight hierarchy is described to the ACPI as follows:
>
>
> +-----------------+
> |                 |
> |       ETM       |
> |                 |
> +--------+--------+
>           |
>           |
> +--------+--------+
> |                 |
> |       ETF       |
> |                 |
> +--------+--------+
>           |
>           |
> +--------+--------+
> |                 |
> |       ETR       |
> |                 |
> +--------+--------+
>           |
>           |
> +--------+--------+
> |                 |
> |      CATU       |
> |                 |
> +--------+--------+
>
> Steve C.

I recreated this in the test here: 
https://lore.kernel.org/linux-kernel/20241217171132.834943-1-james.clark@xxxxxxxxxx/T/#u

But it looks like it correctly selects ETR rather than ETF, so I'm not 
sure what the difference is between your setup and that. If you can have 
a look at that test and compare it that would be very helpful.

Thanks
James