Message-ID: <CAKfTPtDV7NwbH=QhewQD2JXGWwVDjqwVGom35Wx2+Mxpt4kTPA@mail.gmail.com>
Date:   Thu, 3 Nov 2022 11:58:07 +0100
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     Cristian Marussi <cristian.marussi@....com>
Cc:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        sudeep.holla@....com, james.quinlan@...adcom.com,
        Jonathan.Cameron@...wei.com, f.fainelli@...il.com,
        etienne.carriere@...aro.org, souvik.chakravarty@....com,
        wleavitt@...vell.com, peter.hilber@...nsynergy.com,
        nicola.mazzucato@....com, tarek.el-sherbiny@....com,
        quic_kshivnan@...cinc.com
Subject: Re: [PATCH v4 0/11] Introduce a unified API for SCMI Server testing

On Thu, 3 Nov 2022 at 10:21, Cristian Marussi <cristian.marussi@....com> wrote:
>
> On Wed, Nov 02, 2022 at 09:54:50AM +0100, Vincent Guittot wrote:
> > On Fri, 28 Oct 2022 at 18:58, Cristian Marussi <cristian.marussi@....com> wrote:
> > >
> > > On Fri, Oct 28, 2022 at 06:18:52PM +0200, Vincent Guittot wrote:
> > > > On Fri, 28 Oct 2022 at 17:04, Cristian Marussi <cristian.marussi@....com> wrote:
> > > > >
> > > > > On Fri, Oct 28, 2022 at 04:40:02PM +0200, Vincent Guittot wrote:
> > > > > > On Wed, 19 Oct 2022 at 22:46, Cristian Marussi <cristian.marussi@....com> wrote:
> > > > > > >
> > > > > > > Hi all,
> > > > > > >
> > > > >
> > > > > Hi Vincent,
> > > > >
> > > > > > > This series aims to introduce a new SCMI unified userspace interface meant
> > > > > > > to ease testing an SCMI Server implementation for compliance, fuzzing etc.,
> > > > > > > from the perspective of the OSPM agent (non-secure world only ...)
> > > > > > >
> > > >
> > > > [ snip]
> > > >
> > > > > > Hi Cristian,
> > > > > >
> > > > > > I have tested your series with an optee message transport layer and
> > > > > > been able to send raw messages to the scmi server PTA
> > > > > >
> > > > > > FWIW
> > > > > >
> > > > > > Tested-by: Vincent Guittot <vincent.guittot@...aro.org>
> > > > > >
> > > > >
> > > > > Thanks a lot for your test and feedback !
> > > > >
> > > > > ... but I was going to reply to this saying that I spotted another issue
> > > > > with the current SCMI Raw implementation (NOT related to optee/smc) so
> > > > > that I'll post a V5 next week :P
> > > > >
> > > > > Anyway, the issue is much related to the debugfs root used by SCMI Raw,
> > > > > i.e.:
> > > > >
> > > > >         /sys/kernel/debug/scmi_raw/
> > > > >
> > > > > ..this works fine unless you run it on a system sporting multiple DT-defined
> > > > > server instances ...that is not officially supported but....ehm...a little
> > > > > bird told these system with multiple servers do exists :D
> > > >
> > > > ;-)
> > > >
> > > > >
> > > > > In such a case the SCMI core stack is probed multiuple times and so it
> > > > > will try to register multiple debugfs Raw roots: there is no chanche to
> > > > > root the SCMI Raw entries at the same point clearly ... and then anyway
> > > > > there is the issue of recognizing which server is rooted where ... with
> > > > > the additional pain that a server CANNOT be recognized by querying...cause
> > > > > there is only one by teh spec with agentID ZERO ... in theory :D...
> > > > >
> > > > > So my tentaive solution for V5 would be:
> > > > >
> > > > > - change the Raw root debugfs as:
> > > > >
> > > > >         /sys/kernel/debug/scmi_raw/0/... (first server defined)
> > > > >
> > > > >         /sys/kernel/debug/scmi_raw/1/... (possible additional server(s)..)
> > > > >
> > > > > - expose the DT scmi-server root-node name of the server somewhere under
> > > > >   that debugfs root like:
> > > > >
> > > > >         ..../scmi_raw/0/transport_name -> 'scmi-mbx'
> > > > >
> > > > >         ..../scmi_raw/1/transport_name -> 'scmi-virtio'
> > > >
> > > > I was about to say that you would display the server name but that
> > > > means that you have send a request to the server which probably
> > > > defeats the purpose of the raw mode
> > > >
> > > > >
> > > > >   so that if you know HOW you have configured your own system in the DT
> > > > >   (maybe multiple servers with different kind of transports ?), you can
> > > > >   easily select programmatically which one is which, and so decide
> > > > >   which Raw debugfs fs to use...
> > > > >
> > > > > ... I plan to leave the SCMI ACS suite use by default the first system
> > > > > rooted at /sys/kernel/debug/scmi_raw/0/...maybe adding a commandline
> > > > > option to choose an alternative path for SCMI Raw.
> > > > >
> > > > > Does all of this sound reasonable ?
> > > >
> > > > Yes, adding an index looks good to me.
> > >
> > > Ok, I'll rework accordingly.
> > >
> > > >
> > > > As we are there, should we consider adding a per channel entry in the
> > > > tree when there are several channels shared with the same server ?
> > > >
> > >
> > > So, I was thinking about this and, even though, it seems not strictly
> > > needed for Compliance testing (as discussed offline) I do think that
> > > could be a sensible option to have as an additional mean to stress the
> > > server transport implementation (as you wish).
> >
> > Thanks
> >
> > >
> > > Having said that, this week, I was reasoning about an alternative
> > > interface to do this, i.e. to avoid to add even more debugfs entries
> > > for this chosen-channel config or possibly in the future to ask for
> > > transport polling mode (if supported by the underlying transport)
> > >
> > > My idea (not thought fully through as of now eh..) would be as follows:
> > >
> > > since the current Raw implementation enforces a minimum size of 4 bytes
> > > for the injected message (more on this later down below in NOTE), I was
> > > thinking about using less-than-4-bytes-sized messages to sort of
> > > pre-configure the Raw stack.
> > >
> > > IOW, instead of having a number of new additional entries like
> > >
> > >         ../message_ch10
> > >         ../message_ch13
> > >         ../message_poll
> > >
> > > we could design a sort of API (in the API :D) that defines how
> > > 3-bytes message payload are to be interpreted, so that in normal usage
> > > everything will go on as it is now, while if a 3-bytes message is
> > > injected by a specially crafted testcase, it would be used to configure
> > > the behaviour stack for the subsequent set of Raw transactions
> > > (i.e. for the currently opened fd...) like:
> > >
> > > - open message fd
> > >
> > > - send a configure message:
> > >
> > >         | proto_chan_#  |     flags (polling..)  |
> > >         ------------------------------------------
> > >         0               7                       21
> > >
> > > - send/receive your test messages
> > >
> > > - repeat or close (then the config will vanish...)
> > >
> > > This would mean adding some sort entry under scmi_raw to expose the
> > > configured available channels on the system though.
> > >
> > > [maybe the flags above could also include an async flag and avoid
> > >  also to add the message_async entries...]
> > >
> > > I discarded the idea to run the above config process via IOCTLs since
> > > it seemed to me even more frowned upon to use IOCTLs on a debugfs entry
> > > :P...but I maybe wrong ah...
> > >
> > > All of this is still to be explored anyway, any thoughts ? or evident
> > > drawbacks ? (beside having to clearly define an API for these message
> > > config machinery)
> >
> > TBH, I'm not a fan of adding a protocol on top of the SCMI one. This
> > interface aims to test the SCMI servers and their channels so we
> > should focus on this and make it simple to use. IMHO, adding some
> > special bytes before the real scmi message is prone to create
> > complexity and error in the use of this debug interface.
> >
>
> Indeed, even if only for transport-related tests, the risk is to make
> more complicate to use the interface.
>
> Agreed, just wanted to have some feedback. I'll revert to some based on
> debugfs trying to minimize entries and improper usage...maybe something
> like grouping on per-channel subdirs when different channels are
> available.
>
> E.g. on a system with a dedicated PERF channel I could have
>
>
>         ../scmi_raw/0/message             <<< usual auto channel selection
>                      /message_async
>                      ...
>
>                      /chan_0x10/message   <<< use default channel (base proto)
>                                /message_async
>                                ....
>
>                      /chan_0x13/message  <<< use PERF channel
>                                /message_async
>                                ....


The proposal above looks good for me

Thanks

>
> The alternative would be to have a common single entry to configure the usage
> of the a single batch of message/message_async entries BUT that seems to
> me more prone to error, e.g. if you dont clear the special config at the
> end of your special testcase you could endup using custom channels conf also
> with any following regular test which expects to benefit from the
> automatic channel selection (which I still think should be default way of
> running these tests..)
>
> Thoughts ?
>
> Thanks for the feedback.
> Cristian

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