Re: [PATCH 2/2] configs: Add generic qcom_tfa_optee_defconfig

[Sumit Garg <sumit.garg@kernel.org>]

On Thu, Jan 08, 2026 at 05:41:42PM +0100, Casey Connolly wrote:
> 
> 
> On 29/12/2025 12:43, Sumit Garg wrote:
> > From: Sumit Garg <sumit.garg@oss.qualcomm.com>
> > 
> > Recently upstream TF-A/OP-TEE has started gaining support for Qcom
> > platforms. RB3Gen2 being the first one and more to come. U-Boot in
> > corresponding boot flow is packaged as a position independent executable.
> > 
> > So, lets add a generic U-Boot defconfig for Qcom platforms to support
> > TF-A/OP-TEE based TrustZone stack. Build command:
> > 
> > $ make qcom_tfa_optee_defconfig
> > $ make -j`nproc` DEVICE_TREE=qcom/qcs6490-rb3gen2
> 
> This would be better suited as a config fragment rather than a new
> defconfig imo.

That's fine with me to add it as a config fragment.

> 
> But more importantly, enabling OPTEE support in U-Boot doesn't imply
> that it will be used, just that it's supported.

There are real use-cases of OP-TEE in U-Boot for Qcom platforms like
secure EFI variables based on OP-TEE secure storage. Have a look here [1].

And sure there will be more such use-cases like fTPM, KASLR etc. can be
supported based on OP-TEE.

[1] lib/efi_loader/efi_variable_tee.c

> 
> So I think the more appropriate patch here would be to just enable
> OP-TEE in qcom_defconfig (assuming the binary size isn't significantly
> affected).

The OP-TEE driver in U-Boot itself is probed based on DT and it's not
only specific to Qcom platforms but every other platform using OP-TEE.

> 
> Considering the other patch is based on this assumption that if OP-TEE
> support is enabled then the board must be using it, a different approach
> is definitely needed.

Yeah that's true even with TF-A boot flow, there is possibility to boot
without OP-TEE as well. However, TF-A generally doesn't provide a
generic option to detect whether OP-TEE is running or not.

> 
> When I was looking into this last year I remember discussing this same
> issue from the Linux side, there is a good argument to be made that
> OP-TEE support in Linux shouldn't be based on the devicetree -
> particularly in the Qualcomm case where whether or not OP-TEE is used is
> a simple software change, nothing to do with hardware.

Sadly it's true for every other silicon vendor too. But OP-TEE support
based on DT has become an ABI unless migration for OP-TEE support based
on FF-A comes into picture.

> 
> So in general I'm not particularly keen on this approach, I think it
> /might/ be acceptable for U-Boot to have some fixup code to add the
> OP-TEE node if OP-TEE is in use with the idea of phasing that out in
> favour of runtime detection in the OS itself. I'd also expect that fixup
> code to go in the generic U-Boot DT fixup code that runs before we jump
> to the OS (like the EFI DT fixup function).

The EFI DT fixup code is already there based on U-Boot DT. Have a look
here:

boot/image-fdt.c:627:   fdt_ret = optee_copy_fdt_nodes(blob);

In general on Arm platforms there isn't any SMC bus to detect
dynamically if there is support for OP-TEE or not. That's why
platform bus was choosen for the U-Boot and Linux OP-TEE driver. It's
similar to how we have the SCM DT node for Qcom platforms.

FF-A bus tries to solve that problem to unify that approach for future
platform but U-Boot hasn't yet gained support for FF-A based OP-TEE
driver too.

Anyhow, this is the sanest way I can come up with to enable OP-TEE
support in a general way for all the Qcom platforms. This is aligned
with how OP-TEE support is detected for other silicon vendors too.

-Sumit

> 
> Kind regards,
> 
> > 
> > For more information refer here:
> > https://trustedfirmware-a.readthedocs.io/en/latest/plat/qti/rb3gen2.html
> > 
> > Signed-off-by: Sumit Garg <sumit.garg@oss.qualcomm.com>
> > ---
> >  configs/qcom_tfa_optee_defconfig | 7 +++++++
> >  1 file changed, 7 insertions(+)
> >  create mode 100644 configs/qcom_tfa_optee_defconfig
> > 
> > diff --git a/configs/qcom_tfa_optee_defconfig b/configs/qcom_tfa_optee_defconfig
> > new file mode 100644
> > index 00000000000..c398521770f
> > --- /dev/null
> > +++ b/configs/qcom_tfa_optee_defconfig
> > @@ -0,0 +1,7 @@
> > +# Configuration for building a generic U-Boot image
> > +# with support for TF-A/OP-TEE based Arm TrustZone stack.
> > +
> > +#include "qcom_defconfig"
> > +
> > +CONFIG_TEE=y
> > +CONFIG_OPTEE=y
> 
> -- 
> // Casey (she/her)
>