Re: [PATCH 0/6] introduce Arm FF-A support

Tom Rini
2022-04-13T16:46:18Z

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On Wed, Apr 13, 2022 at 03:20:23PM +0100, Abdellatif El Khlifi wrote:
> On Tue, Apr 12, 2022 at 08:28:42AM -0500, Rob Herring wrote:
> > On Tue, Apr 12, 2022 at 7:01 AM Tom Rini <trini@konsulko.com> wrote:
> > >
> > > On Tue, Apr 12, 2022 at 12:43:15PM +0100, Abdellatif El Khlifi wrote:
> > > > On Thu, Apr 07, 2022 at 08:58:11AM -0400, Tom Rini wrote:
> > > > > On Thu, Apr 07, 2022 at 01:54:24PM +0100, Abdellatif El Khlifi wrote:
> > > > > > On Wed, Apr 06, 2022 at 03:47:11PM -0400, Tom Rini wrote:
> > > > > > > On Tue, Mar 29, 2022 at 04:16:53PM +0100, abdellatif.elkhlifi@arm.com wrote:
> > > > > > > > From: Abdellatif El Khlifi <abdellatif.elkhlifi@arm.com>
> > > > > > > >
> > > > > > > > This patchset adds support for Arm FF-A (Arm Firmware Framework for Armv8-A v1.0).
> > > > > > > >
> > > > > > > > FF-A support is generic by design and can be used by any Arm platform.
> > > > > > > >
> > > > > > > > The features added are as follows:
> > > > > > > >
> > > > > > > > 1/ FF-A device driver
> > > > > > > > 2/ armffa command
> > > > > > > > 3/ FF-A Sandbox driver
> > > > > > > > 4/ FF-A Sandbox test cases
> > > > > > > > 5/ FF-A MM communication
> > > > > > > >
> > > > > > > >
> > > > > > > > The suggested design sees FF-A as a data bus allowing data exchange with the firmware
> > > > > > > > running under TrustZone HW (such as Optee). The same approach was followed in the
> > > > > > > > FF-A driver in Linux kernel (https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/firmware/arm_ffa/bus.c?h=v5.15#n211))
> > > > > > > >
> > > > > > > > u-boot boards using FF-A can provide a device tree node in a <board>-u-boot.dtsi file.
> > > > > > > > Since the node can not be hosted in Linux device tree, we suggest using u-boot device tree.
> > > > > > >
> > > > > > > Why can't the node be in the upstream tree? It should be, so that it
> > > > > > > can be shared between all users. Especially since there's in-Linux
> > > > > > > users?
> > > > > > >
> > > > > > > --
> > > > > > > Tom
> > > > > >
> > > > > > Linux already has an FF-A bus driver and doesn't use a device tree node for FF-A.
> > > > > >
> > > > > > The Linux driver registers FF-A as a bus:
> > > > > >
> > > > > > int arm_ffa_bus_init(void)
> > > > > > {
> > > > > > return bus_register(&ffa_bus_type);
> > > > > > }
> > > > > >
> > > > > > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/firmware/arm_ffa/bus.c?h=v5.15#n211
> > > > > >
> > > > > > So, there is no user for the node in Linux. That's why we suggest hosting the node in the u-boot device tree (a u-boot.dtsi file)
> > > > >
> > > > > OK, but you can still push it upstream as it's not required to have an
> > > > > in tree user.
> > > >
> > > > During the review of Corstone-1000 patchset, Rui Silva had a discussion with the Linux device tree maintainer
> > > > (Rob Herring). Rob is not in favour of an FFA node in the kernel device tree. This is why we are including the FFA node
> > > > in u-boot device tree (u-boot.dtsi files).
> >
> > Sigh. There is not a 'kernel device tree' and a 'u-boot device tree'.
> > There is only 1. For SystemReadyIR compliance, that is a hard
> > requirement.
> >
> > > I'm a bit confused now, can you please link to the kernel thread? Or
> > > Rob, can you chime in here please?
> >
> > The FFA DT binding was rejected in favor of making FFA discoverable.
> > The FFA spec was amended to address that. DT is only for what we
> > failed to make discoverable. For hardware, we're stuck with it. We
> > shouldn't repeat that for software interfaces.
> >
> > Rob
>
> Guys,
>
> Since we can not add an FFA node in the device tree, we will make FFA a discoverable bus.
> So, we will manually create the udevice, binding it to the driver and probing it.
> Manually means directly calling device_bind and device_probe APIs.
>
> Any thoughts about this approach ?

How is it both discoverable and doesn't have a device tree node, in the
kernel?

--
Tom

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