linux-kernel - Re: [PATCH 0/2] OP-TEE FF-A notifications

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Date:   Thu, 2 Nov 2023 19:35:13 +0530
From:   Sumit Garg <sumit.garg@...aro.org>
To:     Jens Wiklander <jens.wiklander@...aro.org>
Cc:     linux-kernel@...r.kernel.org, op-tee@...ts.trustedfirmware.org,
        Jerome Forissier <jerome.forissier@...aro.org>,
        Sudeep Holla <sudeep.holla@....com>,
        Marc Bonnici <marc.bonnici@....com>,
        Olivier Deprez <Olivier.Deprez@....com>,
        Lorenzo Pieralisi <lpieralisi@...nel.org>
Subject: Re: [PATCH 0/2] OP-TEE FF-A notifications

On Thu, 2 Nov 2023 at 18:46, Jens Wiklander <jens.wiklander@...aro.org> wrote:
>
> On Thu, Nov 02, 2023 at 05:46:55PM +0530, Sumit Garg wrote:
> > On Thu, 2 Nov 2023 at 17:29, Jens Wiklander <jens.wiklander@...aro.org> wrote:
> > >
> > > Hi Sumit,
> > >
> > > On Mon, Oct 30, 2023 at 11:32:47AM +0530, Sumit Garg wrote:
> > > > Hi Jens,
> > > >
> > > > On Thu, 26 Oct 2023 at 13:34, Jens Wiklander <jens.wiklander@...aro.org> wrote:
> > > > >
> > > > > Hi all,
> > > > >
> > > > > This patchset adds support for using FF-A notifications as a delivery
> > > > > mechanism of asynchronous notifications from OP-TEE running in the secure
> > > > > world. Support for asynchronous notifications via the SMC ABI was added in
> > > > > [1], here we add the counterpart needed when using the the FF-A ABI.
> > > > >
> > > > > Support for FF-A notifications is added with [2] and this patch set is based
> > > > > on Sudeeps tree at [3].
> > > >
> > > > It's good to see FF-A notifications support coming through. The good
> > > > aspect here is that FF-A uses a common secure world SGI for
> > > > notifications and doesn't have to deal with platform specific reserved
> > > > SPI for notifications.
> > > >
> > > > From OP-TEE point of view I think most of the secure SGI donation base
> > > > would be common, so can we switch the SMC ABI to use this donated
> > > > secure world SGI for notifications too?
> > >
> > > The SMC ABI driver picks up the interrupt used for notification from
> > > device-tree, so there's a chance that it just works if a donated SGI is
> > > supplied instead. We'll need some changes in the secure world side of
> > > OP-TEE, but they wouldn't affect the ABI.
> >
> > AFAIK, a secure world donated SGIs doesn't support IRQ mapping via DT.
> > The FF-A driver explicitly creates that mapping here [1].
>
> That looks a lot like what platform_get_irq() does via of_irq_get().
>

There is GIC_SPI or GIC_PPI but nothing like GIC_SGI in DT bindings [1].

[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/include/dt-bindings/interrupt-controller/arm-gic.h

> > Moreover
> > it's better to detect it via an SMC call rather than hard coded via DT
> > as FF-A driver does.
>
> Typo? I guess you mean that you prefer that way the FF-A driver does it
> rather than having it set in the DT.

Yeah sorry about that. We shouldn't use DT if OP-TEE features are discoverable.

>
> Assuming that you only care about "arm,gic-v3". The SGI will likely
> always be the same so it shouldn't be too hard to keep the correct
> configuration in DT.

See above, DT looks like it does not support SGI.

>
> >
> > So the ABI should dynamically detect if there is a donated SGI then
> > use it otherwise fallback to SPI/PPI detection via DT. This would make
> > the notifications feature platform agnostic and we can drop legacy DT
> > methods from optee-os entirely but still need to maintain them in the
> > kernel for backwards compatibility.
>
> We care about compatibility in both directions so we'd need to keep it
> in OP-TEE too, but perhaps under a config flag.

Isn't it just supported on Qemu right now in OP-TEE? I hope dropping a
feature won't be a problem there compared with the maintenance burden.

-Sumit

>
> Thanks,
> Jens
>
> >
> > [1] https://git.kernel.org/pub/scm/linux/kernel/git/sudeep.holla/linux.git/tree/drivers/firmware/arm_ffa/driver.c?h=ffa-updates-6.7#n1283
> > [2] https://git.kernel.org/pub/scm/linux/kernel/git/sudeep.holla/linux.git/tree/drivers/firmware/arm_ffa/driver.c?h=ffa-updates-6.7#n1275
> >
> > -Sumit
> >
> > >
> > > Cheers,
> > > Jens
> > >
> > > >
> > > > -Sumit
> > > >
> > > > >
> > > > > [1] https://lore.kernel.org/lkml/20211103090255.998070-1-jens.wiklander@linaro.org/
> > > > > [2] https://lore.kernel.org/linux-arm-kernel/20231005-ffa_v1-1_notif-v4-0-cddd3237809c@arm.com/
> > > > > [3] https://git.kernel.org/pub/scm/linux/kernel/git/sudeep.holla/linux.git/tag/?h=ffa-updates-6.7
> > > > >     commit bcefd1bf63b1 ("firmware: arm_ffa: Upgrade the driver version to v1.1")
> > > > >
> > > > > Thanks,
> > > > > Jens
> > > > >
> > > > > Jens Wiklander (2):
> > > > >   optee: provide optee_do_bottom_half() as a common function
> > > > >   optee: ffa_abi: add asynchronous notifications
> > > > >
> > > > >  drivers/tee/optee/call.c          | 31 ++++++++++-
> > > > >  drivers/tee/optee/ffa_abi.c       | 91 ++++++++++++++++++++++++++++++-
> > > > >  drivers/tee/optee/optee_ffa.h     | 28 ++++++++--
> > > > >  drivers/tee/optee/optee_private.h |  9 ++-
> > > > >  drivers/tee/optee/smc_abi.c       | 36 ++----------
> > > > >  5 files changed, 153 insertions(+), 42 deletions(-)
> > > > >
> > > > >
> > > > > base-commit: bcefd1bf63b1ec9bb08067021cf47f0fad96f395
> > > > > --
> > > > > 2.34.1
> > > > >