Hi Andrzej

I think recent patch: https://review.trustedfirmware.org/c/TF-A/trusted-firmware-a/+/3493  which is currently in review may be solution for your issue where SCU presence is being checked before accessing CLUSTERCFR_EL1 register.

Thanks
Manish Badarkhe

From: TF-A <tf-a-bounces@lists.trustedfirmware.org> on behalf of "Witkowski, Andrzej via TF-A" <tf-a@lists.trustedfirmware.org>
Reply to: "Witkowski, Andrzej" <andrzej.witkowski@intel.com>
Date: Monday, 1 June 2020 at 19:38
To: "tf-a@lists.trustedfirmware.org" <tf-a@lists.trustedfirmware.org>
Cc: "Witkowski, Andrzej" <andrzej.witkowski@intel.com>, "Lessnau, Adam" <adam.lessnau@intel.com>
Subject: [TF-A] Unhandled Exception at EL3 in BL31 for Neoverse N1 with direct connect of DSU

Hi,

I work on project which uses ARM CPU Neoverse N1 with direct connect of DSU.

I noticed the following error “Unhandled Exception at EL3” in BL31 bootloader after switching from ATF 2.1 to 2.2.

The root cause is that after invoking neoverse_n1_errata-report function in lib/cpus/aarch64/neoverse_n1.S file and reaching the line 525, the function check_errata_dsu_934 in lib/cpus/aarch64/dsu_helpers.S file is always invoked regardless of whether ERRATA_DSU_936184 is set to 0 or to 1.

In our case, ERRATA_DSU_936184 := 0.

Neoverse N1 with direct connect version of DSU doesn’t contain SCU/L3 cache and CLUSTERCFR_EL1 register.

The error “Unhandled Exception at EL3” appears in BL31 bootloader during attempt to read the CLUSTERCFR_EL1 register which doesn’t exist in our RTL HW.

Andrzej Witkowskie

Intel Technology Poland

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