Hi Dan,

In TF-A build system, there is no easy way to disable this flag only for BL2 at the moment. This flag can be either be enabled or disabled for all BL components of the platform.

This is a technical use case, and we have not encountered it as a priority item. Are you expecting performance gains if the FPU is enabled in BL2?

We would be interested in hearing more about the specific use case if you are willing discuss it in the open-forum.

Thanks,

Manish Badarkhe

From: Soby Mathew via TF-A <tf-a@lists.trustedfirmware.org>
Date: Wednesday, 25 May 2022 at 11:41
To: Bartus, Dan <Dan.Bartus@analog.com>, tf-a@lists.trustedfirmware.org <tf-a@lists.trustedfirmware.org>
Cc: Neely, Brian <Brian.Neely@analog.com>
Subject: [TF-A] Re: Floating point math

Hi Dan,

I am a bit rusty on the build system and someone from the core TF-A team will be able to advise on makefile changes. One more thing that you would need to do is set cptr_el3.tfp=0 & cpacr_el1.fpen=0b11  (TF-A disables FP by default at runtime).

Best Regards

Soby Mathew

From: Bartus, Dan <Dan.Bartus@analog.com>
Sent: 24 May 2022 18:03
To: Soby Mathew <Soby.Mathew@arm.com>; tf-a@lists.trustedfirmware.org
Cc: Neely, Brian <Brian.Neely@analog.com>
Subject: RE: Floating point math

Can u suggest a method to disable that flag in BL2 and no where else in platform.mk>?? Possibly using the an ifdef BL2_SOURCES?

From: Soby Mathew <Soby.Mathew@arm.com>
Sent: Tuesday, May 24, 2022 4:51 AM
To: Bartus, Dan <Dan.Bartus@analog.com>; tf-a@lists.trustedfirmware.org
Cc: Neely, Brian <Brian.Neely@analog.com>
Subject: RE: Floating point math

[External]

Hi Dan

Just my 2 cents,
Theoretically it should be possible to use FPU at BL2. BL2 does not context switch between worlds and hence all that is probably required is to enable compiler to use FP.  The current build system in TF-A may be a bit unwieldy because it may not allow remove C flags for a particular BL image , as I remember. The runtime firmware , BL31 should not use FP and hence any changes done to BL2 to enable it to use FP should not affect the BL31 compiler flags.

Best Regards

Soby Mathew

From: Bartus, Dan via TF-A <tf-a@lists.trustedfirmware.org>
Sent: 23 May 2022 21:50
To: tf-a@lists.trustedfirmware.org
Cc: Neely, Brian <Brian.Neely@analog.com>
Subject: [TF-A] Floating point math

We are using an arm ARCH-64  (A55) and we need to do some floating point math in BL2.  It seems this is not enabled. Is there a reason why I cannot do FP math (security issue?) and if I can, how do I enable it?

I am seeing this error when I use floats “-mgeneral-regs-only”

thanks