[U-Boot] [PATCH v2 3/4] image: fdt: copy possible optee nodes to a loaded devicetree

[Heiko Stübner]

Hi Patrick,

Am Mittwoch, 23. Oktober 2019, 09:10:52 CEST schrieb Patrick DELAUNAY:
> Hi Jens and Heiko,
> 
> > From: U-Boot <u-boot-bounces at lists.denx.de> On Behalf Of Jens Wiklander
> > Sent: mercredi 23 octobre 2019 08:46
> > 
> > On Tue, Oct 22, 2019 at 09:04:27PM +0200, Heiko Stuebner wrote:
> > > From: Heiko Stuebner <heiko.stuebner at theobroma-systems.com>
> > >
> > > The loading convention for optee or any other tee on arm64 is as bl32
> > > parameter to the trusted-firmware. So TF-A gets invoked with the TEE
> > > as
> > > bl32 and main u-boot as bl33. Once it has done its startup TF-A jumps
> > > into the bl32 for the TEE startup, returns to TF-A and then jumps to bl33.
> > >
> > > All of them get passed a devicetree as parameter and all components
> > > often get loaded from a FIT image.
> > >
> > > OP-TEE will create additional nodes in that devicetree namely a
> > > firmware node and possibly multiple reserved-memory nodes.
> > >
> > > While this devicetree is used in main u-boot, in most cases it won't
> > > be the one passed to the actual kernel. Instead most boot commands
> > > will load a new devicetree from somewhere like mass storage of the
> > > network, so if that happens u-boot should transfer the optee nodes to that new
> > devicetree.
> > >
> > > To make that happen introduce optee_copy_fdt_nodes() called from the
> > > dt setup function in image-fdt which after checking for the optee
> > > presence in the u-boot dt will make sure a optee node is present in
> > > the kernel dt and transfer any reserved-memory regions it can find.
> > >
> > > Signed-off-by: Heiko Stuebner <heiko.stuebner at theobroma-systems.com>
> > > ---
> > > changes in v2:
> > > - don't create a new optee firmware-node, but instead copy the
> > >   compatible+method properties from the old fdt blob.
> > >
> > >  common/image-fdt.c  |   8 +++
> > >  include/tee/optee.h |   9 +++
> > >  lib/optee/optee.c   | 132 ++++++++++++++++++++++++++++++++++++++++++++
> > >  3 files changed, 149 insertions(+)
> > >
> > [snip]
> 
> On STM32MP1 platform (armv7 with TF-A support), 
> we can use BL32 = OP-TEE or spmin provide by TF-A

That is the same I'm hoping to have at some point for the RK3288
soc I'm also working on :-D .

But why do you need different handling then? Except BL32 being baked
into the TF-A binary on arm32, shouldn't the loading patch be somewhat
similar (SPL -> TF-A -> OP-Tee -> U-Boot) so that OP-Tee also can insert its
nodes there?

(Haven't looked too deeply at this yet)

> So we are plan to have the same type of feature but with an inversed logical:
> 
> - Op-Tee nodes (firmwares and reserved) are present in kernel device tree
> - U-Boot deactivated these nodes when TEE is not present, with the next function called in ft_system_setup:

Having the OP-Tee nodes hard-coded in the devicetree in kernel sources
sounds somewhat counter intuitive to me.

For the firmware node it shouldn't matter much, except that there may
also be other TEEs other than OP-Tee that people may want to load.

But when the reserved memory is hard-coded in the kernel, you bind
yourself to one specific version of your TEE. I.e. what happens when
a future version of your platform support wants to move the memory
region OP-Tee wants to occupy. With OP-Tee handling the reservation
this should be somewhat transparent to bootloader and kernel, as
just the reserved-memory changes.


> static void stm32_fdt_disable_optee(void *blob)
> {
> 	int off, node;
> 
> 	off = fdt_node_offset_by_compatible(blob, -1, "linaro,optee-tz");
> 	if (off >= 0 && fdtdec_get_is_enabled(blob, off))
> 		fdt_status_disabled(blob, off);
> 
> 	/* Disabled "optee at ..." reserved-memory node */
> 	off = fdt_path_offset(blob, "/reserved-memory/");
> 	if (off < 0)
> 		return;
> 	for (node = fdt_first_subnode(blob, off);
> 	     node >= 0;
> 	     node = fdt_next_subnode(blob, node)) {
> 		if (!strncmp(fdt_get_name(blob, node, NULL), "optee@", 6))
> 			fdt_status_disabled(blob, node);
> 	}
> }
> 
> What is  the better for you ?
> 1/ Copy the U-Boot op-tee nodes in kernel device tree (where op-tee nodes was present)
> or 
> 2/ Deactivate the op-tee nodes in kernel device tree (where op-tee nodes are present)
> 
> The advantage of us is to upstream a Linux Kernel device tree with the correct op-tee nodes...

In any case, the copying we're doing here should not affect any present
OP-Tee nodes in the kernel dts and only proceed if both
(a) U-Boot dts does contain an OP-Tee node
(b) Kernel dts does _not yet_ contain an OP-Tee node

are valid.


Heiko

> > Looks good to me:
> > Reviewed-by: Jens Wiklander <jens.wiklander at linaro.org>
> > 
> > Cheers,
> > Jens
> 
> Patrick
>