[PATCH] ARM: stm32: Jump to ep on successful resume in PSCI suspend code

[Marek Vasut]

In case the system has resumed successfully, the PSCI suspend resume
code has to jump to the 'ep' successful resume entry point code path,
otherwise the code has to jump to content of the LR register, which
points to failed resume code path.

To implement this distinction, rewrite LR register stored on stack
with 'ep' value in case of a successful resume, which is really in
every case unless some catastrophic failure occurred during suspend.

Without this change, Linux counts every resume as failed in
/sys/power/suspend_stats/fail

Signed-off-by: Marek Vasut <marex at denx.de>
---
Cc: Patrice Chotard <patrice.chotard at foss.st.com>
Cc: Patrick Delaunay <patrick.delaunay at foss.st.com>
Cc: u-boot at dh-electronics.com
Cc: u-boot at lists.denx.de
Cc: uboot-stm32 at st-md-mailman.stormreply.com
---
 arch/arm/mach-stm32mp/psci.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/arch/arm/mach-stm32mp/psci.c b/arch/arm/mach-stm32mp/psci.c
index 8cdeb0ab3f2..4f2379df45f 100644
--- a/arch/arm/mach-stm32mp/psci.c
+++ b/arch/arm/mach-stm32mp/psci.c
@@ -703,6 +703,8 @@ void __secure psci_system_suspend(u32 __always_unused function_id,
 {
 	u32 saved_mcudivr, saved_pll3cr, saved_pll4cr, saved_mssckselr;
 	u32 gicd_addr = stm32mp_get_gicd_base_address();
+	u32 cpu = psci_get_cpu_id();
+	u32 sp = (u32)__secure_stack_end - (cpu << ARM_PSCI_STACK_SHIFT);
 	bool iwdg1_wake = false;
 	bool iwdg2_wake = false;
 	bool other_wake = false;
@@ -805,4 +807,16 @@ void __secure psci_system_suspend(u32 __always_unused function_id,
 
 	writel(SYSCFG_CMPENR_MPUEN, STM32_SYSCFG_BASE + SYSCFG_CMPENSETR);
 	clrbits_le32(STM32_SYSCFG_BASE + SYSCFG_CMPCR, SYSCFG_CMPCR_SW_CTRL);
+
+	/*
+	 * The system has resumed successfully. Rewrite LR register stored
+	 * on stack with 'ep' value, so that on return from this PSCI call,
+	 * the code would jump to that 'ep' resume entry point code path
+	 * instead of the previous 'lr' register content which (e.g. with
+	 * Linux) points to resume failure code path.
+	 *
+	 * See arch/arm/cpu/armv7/psci.S _smc_psci: for the stack layout
+	 * used here, SP-4 is PC, SP-8 is LR, SP-12 is R7, and so on.
+	 */
+	writel(ep, sp - 8);
 }
-- 
2.43.0