Hi Andrej,

You mean the hardware floatpoint can be used in the Secure Partition?

That’s a good information, can you share us the compiler flags about float-point you are using? Thanks.

/Ken

From: Andrej Butok <andrey.butok@nxp.com>
Sent: Monday, June 1, 2020 2:46 PM
To: Ken Liu <Ken.Liu@arm.com>
Cc: tf-m@lists.trustedfirmware.org
Subject: RE: DSP instructions and FPU use

FYI: >>  Can you do some experiments on enabling hardware float point and see if it is working

In our SDK, the LPC55S HW Float point is enabled for all TFM projects (Kel, GCC/MCUx), and it works.

From: TF-M <tf-m-bounces@lists.trustedfirmware.org> On Behalf Of Ken Liu via TF-M
Sent: Monday, June 1, 2020 8:41 AM
To: tf-m@lists.trustedfirmware.org
Cc: nd <nd@arm.com>
Subject: Re: [TF-M] DSP instructions and FPU use

Hi Cindy,

The reason is we need to estimate the potential security risks after enabling hardware floating-point, so it is set as software FPU as default.

Can you do some experiments on enabling hardware float point and see if it is working, and then let's see the patch? That would be helpful for our estimation.

During bootup, we cleared the CONTROL.FPCA, and if you access hardware float point in a partition thread should work because it would re-invoke the FPCA bit and make everything work as usual. But as I mentioned, we need to estimate it and give a proper solution and then enable your patch.

For DSP, a similar reason is there, we need to take an estimation. But in theory, you can enable the things you have on the hardware, just be caution that the shared resources between S/NS can be the risk (and the resource sharing caused – co-work problem, the context save/load).

Thanks.

/Ken

From: TF-M <tf-m-bounces@lists.trustedfirmware.org> On Behalf Of Cindy Chaumont via TF-M
Sent: Friday, May 29, 2020 6:39 PM
To: tf-m@lists.trustedfirmware.org
Subject: [TF-M] DSP instructions and FPU use

Hello,

I am using the GNUARM compiler and LPCXpresso55S69-EVK dev board and I would like to use DSP instructions and FPU (in secure image).

About FPU, it seems there is no way to use the hardware floating-point support instead of the software support (see "-msoft-float" flag in CommonConfig.cmake file).

Is there a reason for that? Maybe some performance reasons?

About DSP, in CompilerGNUARMxy.cmake files, architecture definition is preferred to CPU type and, in my case, "-march=armv8-m.main" flags is chosen (without +dsp option). The solution I found is to only define ARM_CPU_TYPE (and not ARM_CPU_ARCHITECTURE) to use "-mcpu=cortex-m33" flag instead of "-march=armv8-m.main". So I can use DSP instructions. However, I am not sure if this is the best solution. Maybe an option could be added to allow or not the use of DSP instructions?

Thank you in advance for the answer,

Best regards,

Cindy