[PATCH v2] ARM: stm32: Initialize TAMP_SMCR BKP..PROT fields on STM32MP15xx

[Marek Vasut]

In case of an OTP-CLOSED STM32MP15xx system, the CPU core 1 cannot be
released from endless loop in BootROM only by populating TAMP BKPxR 4
and 5 with magic and branch address and sending SGI0 interrupt from
core 0 to core 1 twice. TAMP_SMCR BKP..PROT fields must be initialized
as well to release the core 1 from endless loop during the second SGI0
handling on core 1. Initialize TAMP_SMCR to protect the first 16 backup
registers, the ones which contain the core 1 magic, branch address and
boot information.

This requirement seems to be undocumented, therefore it was necessary
to trace and analyze the STM32MP15xx BootROM using OpenOCD and objdump.
Ultimately, it turns out that a certain BootROM function reads out the
TAMP_SMCR register and tests whether the BKP..PROT fields are non-zero.
If they are zero, the BootROM code again waits for SGI0 using WFI, else
the execution moves forward until it reaches handoff to the TAMP BKPxR 5
branch address.

This fixes CPU core 1 release using U-Boot PSCI implementation on an
OTP-CLOSED system, i.e. system with fuse 0 bit 6 set.

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
---
V2: Fix up the BKPRWD/BKPWD mask typo
---
 arch/arm/mach-stm32mp/stm32mp1/stm32mp15x.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/arch/arm/mach-stm32mp/stm32mp1/stm32mp15x.c b/arch/arm/mach-stm32mp/stm32mp1/stm32mp15x.c
index dd99150fbc2..a2496361e01 100644
--- a/arch/arm/mach-stm32mp/stm32mp1/stm32mp15x.c
+++ b/arch/arm/mach-stm32mp/stm32mp1/stm32mp15x.c
@@ -14,6 +14,7 @@
 #include <asm/arch/sys_proto.h>
 #include <dm/device.h>
 #include <dm/uclass.h>
+#include <linux/bitfield.h>
 
 /* RCC register */
 #define RCC_TZCR		(STM32_RCC_BASE + 0x00)
@@ -41,6 +42,9 @@
 #define TZC_REGION_ID_ACCESS0	(STM32_TZC_BASE + 0x114)
 
 #define TAMP_CR1		(STM32_TAMP_BASE + 0x00)
+#define TAMP_SMCR		(STM32_TAMP_BASE + 0x20)
+#define TAMP_SMCR_BKPRWDPROT	GENMASK(7, 0)
+#define TAMP_SMCR_BKPWDPROT	GENMASK(23, 16)
 
 #define PWR_CR1			(STM32_PWR_BASE + 0x00)
 #define PWR_MCUCR		(STM32_PWR_BASE + 0x14)
@@ -136,6 +140,18 @@ static void security_init(void)
 	 */
 	writel(0x0, TAMP_CR1);
 
+	/*
+	 * TAMP: Configure non-zero secure protection settings. This is
+	 * checked by BootROM function 35ac on OTP-CLOSED device during
+	 * CPU core 1 release from endless loop. If secure protection
+	 * fields are zero, the core 1 is not released from endless
+	 * loop on second SGI0.
+	 */
+	clrsetbits_le32(TAMP_SMCR,
+			TAMP_SMCR_BKPRWDPROT | TAMP_SMCR_BKPWDPROT,
+			FIELD_PREP(TAMP_SMCR_BKPRWDPROT, 0x10) |
+			FIELD_PREP(TAMP_SMCR_BKPWDPROT, 0x10));
+
 	/* GPIOZ: deactivate the security */
 	writel(BIT(0), RCC_MP_AHB5ENSETR);
 	writel(0x0, GPIOZ_SECCFGR);
-- 
2.43.0