Re: [RFC PATCH 0/8] coresight: syscfg: dynamic load, resource management

[Mathieu Poirier <mathieu.poirier@linaro.org>]

On Wed, May 19, 2021 at 10:43:03AM +0100, Mike Leach wrote:
> Hi Suzuki,
> 
> On Tue, 18 May 2021 at 19:31, Suzuki K Poulose <suzuki.poulose@arm.com> wrote:
> >
> > Hi Mike
> >
> > On 12/05/2021 22:17, Mike Leach wrote:
> >
> > > This patchset represents the second phase of CoreSight configuration
> > > management.
> >
> > Thanks for the series.
> >
> > >
> > > 1) API updated to allow dynamic load and unload of configurations and
> > > features. Dependency management between loaded sets is added.
> > >
> > > 2) New configuration and feature sets can be added using a loadable module.
> > > An example in /samples/coresight is provided to demonstrate this.
> >
> > Is it possible to do this at runtime configfs ? I thought we tied this
> > to configfs for this feautre.
> >
> > While the module approach works, I feel is a hinderance for wider
> > adoption and is something that doesn't allow for use on production
> > systems.
> >
> > >
> > > 3) Resource management API is added. This allows the system to ensure that
> > > loaded configurations and features are only loaded onto devices that can
> > > support them.
> > >
> > > Further - it ensures that configurations with multiple features cannot over
> > > allocate resources.
> > >
> > > 4) configfs can be used to activate a configuration which will then be used
> > > when controlling tracing using sysfs.
> > >
> > > 5) Resource management is added to ETMv4 configurations. This allows current
> > > and future features and configurations to be defined in terms of resources
> > > used as well as registers to be programmed.
> > >
> > > Defining features in this way allows the resource management to operate
> > > correctly.
> > >
> > > The perf event parsing is also adjusted to allow the ETM resources requested
> > > on the command line (e.g. address filters, etc) to be correctly handled
> > > using resoruce management alongside the complex configurations such as
> > > autofdo.
> > >
> > > Applies to coresight/next - which is 5.13-rc1 + initial Coresight configuration
> > > patchset.
> > >
> > > To follow in future revisions / sets:-
> > > a) load of additional config and features by configfs
> >
> > Is this something that implements what I requested above ?
> > Then I don't see how the module approach will be used once that is in
> > place and we will be left with something to maintain forever.
> >
> 
> The first couple of patches in this set implement the dynamic load and
> unload of configurations on top of the existing static load only
> infrastructure from the baseline set.
> This code is used when dynamic loading from both a module and in the
> case of a configfs load. So there is very little code that is specific
> to the module load case.
> 
> The module load was requested by Mathieu as a way of loading new
> configurations and I guess even in production environments, approved
> modules can be loaded at boot to provide standard configs should
> people want them - after all the coresight modules themselves have to
> be loaded.

The goal in making the complex configurations dynamically configurable was to
avoid bloat of the driver.  I don't know how many new implemenation we'll end up
with but I'd rather provision for a large number now rather than having to
backtrack in a couple of years from now.

If I recall correctly we discussed the possibility of having all complex configuration go
through configfs and be added from user space, i.e no static or module elements.
But there were scenarios (and I can't recall those) where static/module elements
were needed, which got us to the current implementation.

If my assesment of the situation is erroneous and static/module elements are not
needed then I'd be in favour a configfs only solution.

> 
> Also - the module load tests the new code very nicely.
> 
> Regards
> 
> Mike
> 
> 
> 
> > Suzuki
> >
> > > b) ECT and CTI and other Coresight components support for configuration and
> > > features.
> > >
> > >
> > > Mike Leach (8):
> > >    coresight: syscfg: Update API to allow dynamic load and unload
> > >    coresight: syscfg: Update load API for config loadable modules
> > >    coresight: syscfg: Example CoreSight configuration loadable module
> > >    coresight: configfs: Allow configfs to activate configuration.
> > >    coresight: syscfg: Add API to check and validate device resources.
> > >    coresight: etm4x: syscfg: Add resource management to etm4x.
> > >    coresight: etm4x: Update perf event resource handling.
> > >    coresight: etm4x: Update configuration example.
> > >
> > >   MAINTAINERS                                   |   1 +
> > >   .../hwtracing/coresight/coresight-cfg-afdo.c  |  38 +-
> > >   .../coresight/coresight-cfg-preload.c         |   9 +-
> > >   .../hwtracing/coresight/coresight-config.c    |  71 ++-
> > >   .../hwtracing/coresight/coresight-config.h    |  45 +-
> > >   .../hwtracing/coresight/coresight-etm4x-cfg.c | 533 ++++++++++++++++++
> > >   .../hwtracing/coresight/coresight-etm4x-cfg.h | 196 ++++++-
> > >   .../coresight/coresight-etm4x-core.c          | 250 +++-----
> > >   .../coresight/coresight-syscfg-configfs.c     |  87 +++
> > >   .../coresight/coresight-syscfg-configfs.h     |   4 +
> > >   .../hwtracing/coresight/coresight-syscfg.c    | 390 +++++++++++--
> > >   .../hwtracing/coresight/coresight-syscfg.h    |  38 +-
> > >   include/linux/coresight.h                     |   2 +
> > >   samples/Kconfig                               |   9 +
> > >   samples/Makefile                              |   1 +
> > >   samples/coresight/Makefile                    |   4 +
> > >   samples/coresight/coresight-cfg-sample.c      |  73 +++
> > >   17 files changed, 1511 insertions(+), 240 deletions(-)
> > >   create mode 100644 samples/coresight/Makefile
> > >   create mode 100644 samples/coresight/coresight-cfg-sample.c
> > >
> >
> 
> 
> --
> Mike Leach
> Principal Engineer, ARM Ltd.
> Manchester Design Centre. UK

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel