[PATCH] ARM: stm32: Report OTP-CLOSED instead of rev.? on closed STM32MP15xx

[Marek Vasut]

SoC revision is only accessible via DBUMCU IDC register,
which requires BSEC.DENABLE DBGSWENABLE bit to be set to
make the register accessible, otherwise an access to the
register triggers bus fault. As BSEC.DBGSWENABLE is zero
in case of an OTP-CLOSED system, do NOT set DBGSWENABLE
bit as this might open a brief window for timing attacks.
Instead, report that this system is OTP-CLOSED and do not
report any SoC revision to avoid confusing users. Use an
SEC/C abbreviation to avoid growing SOC_NAME_SIZE .

Signed-off-by: Marek Vasut <marex at denx.de>
---
Cc: Igor Opaniuk <igor.opaniuk at foundries.io>
Cc: Patrice Chotard <patrice.chotard at foss.st.com>
Cc: Patrick Delaunay <patrick.delaunay at foss.st.com>
Cc: Simon Glass <sjg at chromium.org
Cc: Simon Glass <sjg at chromium.org>
Cc: Tom Rini <trini at konsulko.com>
Cc: u-boot at dh-electronics.com
Cc: uboot-stm32 at st-md-mailman.stormreply.com
---
 arch/arm/mach-stm32mp/stm32mp1/stm32mp15x.c | 19 +++++++++++++++++--
 1 file changed, 17 insertions(+), 2 deletions(-)

diff --git a/arch/arm/mach-stm32mp/stm32mp1/stm32mp15x.c b/arch/arm/mach-stm32mp/stm32mp1/stm32mp15x.c
index afc56b02eea..dd99150fbc2 100644
--- a/arch/arm/mach-stm32mp/stm32mp1/stm32mp15x.c
+++ b/arch/arm/mach-stm32mp/stm32mp1/stm32mp15x.c
@@ -322,8 +322,23 @@ void get_soc_name(char name[SOC_NAME_SIZE])
 
 	get_cpu_string_offsets(&type, &pkg, &rev);
 
-	snprintf(name, SOC_NAME_SIZE, "STM32MP%s%s Rev.%s",
-		 soc_type[type], soc_pkg[pkg], soc_rev[rev]);
+	if (bsec_dbgswenable()) {
+		snprintf(name, SOC_NAME_SIZE, "STM32MP%s%s Rev.%s",
+			 soc_type[type], soc_pkg[pkg], soc_rev[rev]);
+	} else {
+		/*
+		 * SoC revision is only accessible via DBUMCU IDC register,
+		 * which requires BSEC.DENABLE DBGSWENABLE bit to be set to
+		 * make the register accessible, otherwise an access to the
+		 * register triggers bus fault. As BSEC.DBGSWENABLE is zero
+		 * in case of an OTP-CLOSED system, do NOT set DBGSWENABLE
+		 * bit as this might open a brief window for timing attacks.
+		 * Instead, report that this system is OTP-CLOSED and do not
+		 * report any SoC revision to avoid confusing users.
+		 */
+		snprintf(name, SOC_NAME_SIZE, "STM32MP%s%s SEC/C",
+			 soc_type[type], soc_pkg[pkg]);
+	}
 }
 
 static void setup_soc_type_pkg_rev(void)
-- 
2.43.0