Date:   Thu, 28 Oct 2021 12:08:57 +0200
From:   Etienne Carriere <etienne.carriere@...aro.org>
To:     Cristian Marussi <cristian.marussi@....com>
Cc:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        Sudeep Holla <sudeep.holla@....com>,
        Vincent Guittot <vincent.guittot@...aro.org>
Subject: Re: [PATCH v7 2/2] firmware: arm_scmi: Add optee transport

Hello Cristian,

On Thu, 28 Oct 2021 at 11:26, Cristian Marussi <cristian.marussi@....com> wrote:
>
> On Thu, Oct 28, 2021 at 09:53:44AM +0200, Etienne Carriere wrote:
> > Add a new transport channel to the SCMI firmware interface driver for
> > SCMI message exchange based on optee transport channel. The optee
> > transport is realized by connecting and invoking OP-TEE SCMI service
> > interface PTA.
> >
>
> Hi Etienne,
>
> I was going to just add Reviewed-by...but...
>
> > Optee transport support (CONFIG_ARM_SCMI_TRANSPORT_OPTEE) is default
> > enabled when optee driver (CONFIG_OPTEE) is enabled. Effective optee
> > transport is setup upon OP-TEE SCMI service discovery at optee
> > device initialization. For this SCMI UUID is registered to the optee
> > bus for probing. This is done from the link_supplier operator of the
> > SCMI optee transport.
> >
> > The optee transport can use a statically defined shared memory in
> > which case SCMI device tree node defines it using an "arm,scmi-shmem"
> > compatible phandle through property shmem. Alternatively, optee transport
> > allocates the shared memory buffer from the optee driver when no shmem
> > property is defined.
> >
> > The protocol used to exchange SCMI message over that shared memory is
> > negotiated between optee transport driver and the OP-TEE service through
> > capabilities exchange.
> >
> > OP-TEE SCMI service is integrated in OP-TEE since its release tag 3.13.0.
> > The service interface is published in [1].
> >
> > Link: [1] https://github.com/OP-TEE/optee_os/blob/3.13.0/lib/libutee/include/pta_scmi_client.h
> > Cc: Cristian Marussi <cristian.marussi@....com>
> > Cc: Sudeep Holla <sudeep.holla@....com>
> > Signed-off-by: Etienne Carriere <etienne.carriere@...aro.org>
>
> I build tested again...and booted without using it really, just to try load/unload
> of the core SCMI module (so building with ARM_SCMI_PROTOCOL=m) and unfortunately
> I spotted this warning:
>
> root@...-buster-arm64:~# insmod ./scmi-module.ko
> root@...-buster-arm64:~# rmmod ./scmi-module.ko
>
> [   99.860225] ------------[ cut here ]------------
> [   99.865006] Unexpected driver unregister!
> [   99.869116] WARNING: CPU: 0 PID: 339 at drivers/base/driver.c:194 driver_unregister+0x50/0x60
> [   99.877684] Modules linked in: scmi_module(-) [last unloaded: scmi_hwmon]
> [   99.884501] CPU: 0 PID: 339 Comm: rmmod Not tainted 5.15.0-rc1-00003-g46a1949d5e4f #8
> [   99.892352] Hardware name: ARM LTD ARM Juno Development Platform/ARM Juno Development Platform, BIOS EDK II Jun 30 2020
> [   99.903156] pstate: 40000005 (nZcv daif -PAN -UAO -TCO -DIT -SSBS BTYPE=--)
> [   99.910136] pc : driver_unregister+0x50/0x60
> [   99.914419] lr : driver_unregister+0x50/0x60
> [   99.918701] sp : ffff80001259bd50
> [   99.922018] x29: ffff80001259bd50 x28: ffff0008010a5280 x27: 0000000000000000
> [   99.929182] x26: 0000000000000000 x25: 0000000000000000 x24: 0000000000000000
> [   99.936344] x23: 0000000000000000 x22: ffff8000121446d8 x21: ffff800011e19948
> [   99.943506] x20: ffff800011ea7548 x19: ffff80000900b340 x18: 0000000000000010
> [   99.950669] x17: 31333d4d554e5145 x16: 53007375623d4d45 x15: 000000000000017c
> [   99.957831] x14: ffff80001259ba60 x13: 00000000ffffffea x12: ffff800011ea2e70
> [   99.964994] x11: 0000000000000003 x10: ffff800011e8ae30 x9 : ffff800011e8ae88
> [   99.972156] x8 : 0000000000017fe8 x7 : c0000000ffffefff x6 : ffff00097ef4e988
> [   99.979318] x5 : ffff00097ef4e988 x4 : 0000000000000000 x3 : ffff00097ef51910
> [   99.986480] x2 : ffff00097ef51910 x1 : c33162034fce8d00 x0 : 0000000000000000
> [   99.993643] Call trace:
> [   99.996092]  driver_unregister+0x50/0x60
> [  100.000028]  scmi_optee_exit+0x1c/0x28 [scmi_module]
> [  100.005040]  scmi_driver_exit+0x58/0x7c [scmi_module]
> [  100.010131]  __arm64_sys_delete_module+0x19c/0x228
> [  100.014938]  invoke_syscall+0x44/0x108
> [  100.018700]  el0_svc_common.constprop.3+0x94/0xf8
> [  100.023418]  do_el0_svc+0x24/0x88
> [  100.026743]  el0_svc+0x20/0x50
> [  100.029807]  el0t_64_sync_handler+0x90/0xb8
> [  100.034001]  el0t_64_sync+0x180/0x184
> [  100.037674] ---[ end trace 4c09a5e866689fa7 ]---
>
> I suppose it could be that on my system I have not defined an OPTEE DT node, so
> the transport is NEVER initialized (and driver_register) since you are doing it
> in .link_supplier not in .transport_init, BUT then it is indeed always .exited
> by the usual .transport_exit.
>
> I would recommend adding a check on your exit to avoid this (probably using
> scmi_optee_private to avoid unregistering if never registered ?).

Fully make sense, yes. If transport was not initialized (from scmi
link_supplier), it cannot be unregistered (from scmi transport_exit).
I'll follow your suggestion.

>
> Sorry, I think I thought about telling you about this check on .exit in previous
> version but I did not eventaully.

Don't be sorry and many thanks again for the reviews, feedback and guidelines.

>
> Additionally, I have a slight concern if default-enabling it or not; as an
> example virtio is default-N just because it felt like a more esoteric
> transport not generally needed...but this will probably change indeed with all the
> work you guys are doing on virtualizing the stack, so no strong opinion here ...
>
> ...and I'll happily let Sudeep decide on this :D.

Sure. From my view, once both CONFIG_ARM_SCMI_PROTOCOL and
CONFIG_OPTEE are enabled, we can enable SCMI optee transport since it
will be initialized only upon discovery of the OP-TEE firmware SCMI
service (using the tee bus).

Cheers,
Etienne

>
> Thanks,
> Cristian

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