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Subject[RFC PATCH 3/8] RISC-V: Add arch functions for non-retentive suspend entry/exit
Date
The hart registers and CSRs are not preserved in non-retentative
suspend state so we provide arch specific helper functions which
will save/restore hart context upon entry/exit to non-retentive
suspend state. These helper functions can be used by cpuidle
drivers for non-retentive suspend entry/exit.

Signed-off-by: Anup Patel <anup.patel@wdc.com>
---
arch/riscv/include/asm/suspend.h | 35 +++++++++
arch/riscv/kernel/Makefile | 2 +
arch/riscv/kernel/asm-offsets.c | 3 +
arch/riscv/kernel/suspend.c | 86 ++++++++++++++++++++++
arch/riscv/kernel/suspend_entry.S | 116 ++++++++++++++++++++++++++++++
5 files changed, 242 insertions(+)
create mode 100644 arch/riscv/include/asm/suspend.h
create mode 100644 arch/riscv/kernel/suspend.c
create mode 100644 arch/riscv/kernel/suspend_entry.S

diff --git a/arch/riscv/include/asm/suspend.h b/arch/riscv/include/asm/suspend.h
new file mode 100644
index 000000000000..63e9f434fb89
--- /dev/null
+++ b/arch/riscv/include/asm/suspend.h
@@ -0,0 +1,35 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (c) 2021 Western Digital Corporation or its affiliates.
+ */
+
+#ifndef _ASM_RISCV_SUSPEND_H
+#define _ASM_RISCV_SUSPEND_H
+
+#include <asm/ptrace.h>
+
+struct suspend_context {
+ /* Saved and restored by low-level functions */
+ struct pt_regs regs;
+ /* Saved and restored by high-level functions */
+ unsigned long scratch;
+ unsigned long tvec;
+ unsigned long ie;
+#ifdef CONFIG_MMU
+ unsigned long satp;
+#endif
+};
+
+/* Low-level CPU suspend entry function */
+int __cpu_suspend_enter(struct suspend_context *context);
+
+/* High-level CPU suspend which will save context and call finish() */
+int cpu_suspend(unsigned long arg,
+ int (*finish)(unsigned long arg,
+ unsigned long entry,
+ unsigned long context));
+
+/* Low-level CPU resume entry function */
+int __cpu_resume_enter(unsigned long hartid, unsigned long context);
+
+#endif
diff --git a/arch/riscv/kernel/Makefile b/arch/riscv/kernel/Makefile
index f6caf4d9ca15..d83038bf93b2 100644
--- a/arch/riscv/kernel/Makefile
+++ b/arch/riscv/kernel/Makefile
@@ -40,6 +40,8 @@ obj-$(CONFIG_SMP) += cpu_ops_spinwait.o
obj-$(CONFIG_MODULES) += module.o
obj-$(CONFIG_MODULE_SECTIONS) += module-sections.o

+obj-$(CONFIG_CPU_PM) += suspend_entry.o suspend.o
+
obj-$(CONFIG_FUNCTION_TRACER) += mcount.o ftrace.o
obj-$(CONFIG_DYNAMIC_FTRACE) += mcount-dyn.o

diff --git a/arch/riscv/kernel/asm-offsets.c b/arch/riscv/kernel/asm-offsets.c
index b79ffa3561fd..8259f5f16da8 100644
--- a/arch/riscv/kernel/asm-offsets.c
+++ b/arch/riscv/kernel/asm-offsets.c
@@ -10,6 +10,7 @@
#include <linux/sched.h>
#include <asm/thread_info.h>
#include <asm/ptrace.h>
+#include <asm/suspend.h>

void asm_offsets(void);

@@ -108,6 +109,8 @@ void asm_offsets(void)
OFFSET(PT_BADADDR, pt_regs, badaddr);
OFFSET(PT_CAUSE, pt_regs, cause);

+ OFFSET(SUSPEND_CONTEXT_REGS, suspend_context, regs);
+
/*
* THREAD_{F,X}* might be larger than a S-type offset can handle, but
* these are used in performance-sensitive assembly so we can't resort
diff --git a/arch/riscv/kernel/suspend.c b/arch/riscv/kernel/suspend.c
new file mode 100644
index 000000000000..49dddec30e99
--- /dev/null
+++ b/arch/riscv/kernel/suspend.c
@@ -0,0 +1,86 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (c) 2021 Western Digital Corporation or its affiliates.
+ */
+
+#include <linux/ftrace.h>
+#include <asm/csr.h>
+#include <asm/suspend.h>
+
+static void suspend_save_csrs(struct suspend_context *context)
+{
+ context->scratch = csr_read(CSR_SCRATCH);
+ context->tvec = csr_read(CSR_TVEC);
+ context->ie = csr_read(CSR_IE);
+
+ /*
+ * No need to save/restore IP CSR (i.e. MIP or SIP) because:
+ *
+ * 1. For no-MMU (M-mode) kernel, the bits in MIP are set by
+ * external devices (such as interrupt controller, timer, etc).
+ * 2. For MMU (S-mode) kernel, the bits in SIP are set by
+ * M-mode firmware and external devices (such as interrupt
+ * controller, etc).
+ */
+
+#ifdef CONFIG_MMU
+ context->satp = csr_read(CSR_SATP);
+#endif
+}
+
+static void suspend_restore_csrs(struct suspend_context *context)
+{
+ csr_write(CSR_SCRATCH, context->scratch);
+ csr_write(CSR_TVEC, context->tvec);
+ csr_write(CSR_IE, context->ie);
+
+#ifdef CONFIG_MMU
+ csr_write(CSR_SATP, context->satp);
+#endif
+}
+
+int cpu_suspend(unsigned long arg,
+ int (*finish)(unsigned long arg,
+ unsigned long entry,
+ unsigned long context))
+{
+ int rc = 0;
+ struct suspend_context context = { 0 };
+
+ /* Finisher should be non-NULL */
+ if (!finish)
+ return -EINVAL;
+
+ /* Save additional CSRs*/
+ suspend_save_csrs(&context);
+
+ /*
+ * Function graph tracer state gets incosistent when the kernel
+ * calls functions that never return (aka finishers) hence disable
+ * graph tracing during their execution.
+ */
+ pause_graph_tracing();
+
+ /* Save context on stack */
+ if (__cpu_suspend_enter(&context)) {
+ /* Call the finisher */
+ rc = finish(arg, __pa_symbol(__cpu_resume_enter),
+ (ulong)&context);
+
+ /*
+ * Should never reach here, unless the suspend finisher
+ * fails. Successful cpu_suspend() should return from
+ * __cpu_resume_entry()
+ */
+ if (!rc)
+ rc = -EOPNOTSUPP;
+ }
+
+ /* Enable function graph tracer */
+ unpause_graph_tracing();
+
+ /* Restore additional CSRs */
+ suspend_restore_csrs(&context);
+
+ return rc;
+}
diff --git a/arch/riscv/kernel/suspend_entry.S b/arch/riscv/kernel/suspend_entry.S
new file mode 100644
index 000000000000..dee85c86e177
--- /dev/null
+++ b/arch/riscv/kernel/suspend_entry.S
@@ -0,0 +1,116 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (c) 2021 Western Digital Corporation or its affiliates.
+ */
+
+#include <linux/linkage.h>
+#include <asm/asm.h>
+#include <asm/asm-offsets.h>
+#include <asm/csr.h>
+
+ .text
+ .altmacro
+ .option norelax
+
+ENTRY(__cpu_suspend_enter)
+ /* Save registers (except A0 and T0-T6) */
+ REG_S ra, (SUSPEND_CONTEXT_REGS + PT_RA)(a0)
+ REG_S sp, (SUSPEND_CONTEXT_REGS + PT_SP)(a0)
+ REG_S gp, (SUSPEND_CONTEXT_REGS + PT_GP)(a0)
+ REG_S tp, (SUSPEND_CONTEXT_REGS + PT_TP)(a0)
+ REG_S s0, (SUSPEND_CONTEXT_REGS + PT_S0)(a0)
+ REG_S s1, (SUSPEND_CONTEXT_REGS + PT_S1)(a0)
+ REG_S a1, (SUSPEND_CONTEXT_REGS + PT_A1)(a0)
+ REG_S a2, (SUSPEND_CONTEXT_REGS + PT_A2)(a0)
+ REG_S a3, (SUSPEND_CONTEXT_REGS + PT_A3)(a0)
+ REG_S a4, (SUSPEND_CONTEXT_REGS + PT_A4)(a0)
+ REG_S a5, (SUSPEND_CONTEXT_REGS + PT_A5)(a0)
+ REG_S a6, (SUSPEND_CONTEXT_REGS + PT_A6)(a0)
+ REG_S a7, (SUSPEND_CONTEXT_REGS + PT_A7)(a0)
+ REG_S s2, (SUSPEND_CONTEXT_REGS + PT_S2)(a0)
+ REG_S s3, (SUSPEND_CONTEXT_REGS + PT_S3)(a0)
+ REG_S s4, (SUSPEND_CONTEXT_REGS + PT_S4)(a0)
+ REG_S s5, (SUSPEND_CONTEXT_REGS + PT_S5)(a0)
+ REG_S s6, (SUSPEND_CONTEXT_REGS + PT_S6)(a0)
+ REG_S s7, (SUSPEND_CONTEXT_REGS + PT_S7)(a0)
+ REG_S s8, (SUSPEND_CONTEXT_REGS + PT_S8)(a0)
+ REG_S s9, (SUSPEND_CONTEXT_REGS + PT_S9)(a0)
+ REG_S s10, (SUSPEND_CONTEXT_REGS + PT_S10)(a0)
+ REG_S s11, (SUSPEND_CONTEXT_REGS + PT_S11)(a0)
+
+ /* Save CSRs */
+ csrr t0, CSR_EPC
+ REG_S t0, (SUSPEND_CONTEXT_REGS + PT_EPC)(a0)
+ csrr t0, CSR_STATUS
+ REG_S t0, (SUSPEND_CONTEXT_REGS + PT_STATUS)(a0)
+ csrr t0, CSR_TVAL
+ REG_S t0, (SUSPEND_CONTEXT_REGS + PT_BADADDR)(a0)
+ csrr t0, CSR_CAUSE
+ REG_S t0, (SUSPEND_CONTEXT_REGS + PT_CAUSE)(a0)
+
+ /* Return non-zero value */
+ li a0, 1
+
+ /* Return to C code */
+ ret
+END(__cpu_suspend_enter)
+
+ENTRY(__cpu_resume_enter)
+#ifdef CONFIG_MMU
+ /* Save A0 and A1 */
+ add t0, a0, zero
+ add t1, a1, zero
+
+ /* Enable MMU */
+ la a0, swapper_pg_dir
+ call relocate_enable_mmu
+
+ /* Restore A0 and A1 */
+ add a0, t0, zero
+ add a1, t1, zero
+#endif
+
+ /* Make A0 point to suspend context */
+ add a0, a1, zero
+
+ /* Restore CSRs */
+ REG_L t0, (SUSPEND_CONTEXT_REGS + PT_EPC)(a0)
+ csrw CSR_EPC, t0
+ REG_L t0, (SUSPEND_CONTEXT_REGS + PT_STATUS)(a0)
+ csrw CSR_STATUS, t0
+ REG_L t0, (SUSPEND_CONTEXT_REGS + PT_BADADDR)(a0)
+ csrw CSR_TVAL, t0
+ REG_L t0, (SUSPEND_CONTEXT_REGS + PT_CAUSE)(a0)
+ csrw CSR_CAUSE, t0
+
+ /* Restore registers (except A0 and T0-T6) */
+ REG_L ra, (SUSPEND_CONTEXT_REGS + PT_RA)(a0)
+ REG_L sp, (SUSPEND_CONTEXT_REGS + PT_SP)(a0)
+ REG_L gp, (SUSPEND_CONTEXT_REGS + PT_GP)(a0)
+ REG_L tp, (SUSPEND_CONTEXT_REGS + PT_TP)(a0)
+ REG_L s0, (SUSPEND_CONTEXT_REGS + PT_S0)(a0)
+ REG_L s1, (SUSPEND_CONTEXT_REGS + PT_S1)(a0)
+ REG_L a1, (SUSPEND_CONTEXT_REGS + PT_A1)(a0)
+ REG_L a2, (SUSPEND_CONTEXT_REGS + PT_A2)(a0)
+ REG_L a3, (SUSPEND_CONTEXT_REGS + PT_A3)(a0)
+ REG_L a4, (SUSPEND_CONTEXT_REGS + PT_A4)(a0)
+ REG_L a5, (SUSPEND_CONTEXT_REGS + PT_A5)(a0)
+ REG_L a6, (SUSPEND_CONTEXT_REGS + PT_A6)(a0)
+ REG_L a7, (SUSPEND_CONTEXT_REGS + PT_A7)(a0)
+ REG_L s2, (SUSPEND_CONTEXT_REGS + PT_S2)(a0)
+ REG_L s3, (SUSPEND_CONTEXT_REGS + PT_S3)(a0)
+ REG_L s4, (SUSPEND_CONTEXT_REGS + PT_S4)(a0)
+ REG_L s5, (SUSPEND_CONTEXT_REGS + PT_S5)(a0)
+ REG_L s6, (SUSPEND_CONTEXT_REGS + PT_S6)(a0)
+ REG_L s7, (SUSPEND_CONTEXT_REGS + PT_S7)(a0)
+ REG_L s8, (SUSPEND_CONTEXT_REGS + PT_S8)(a0)
+ REG_L s9, (SUSPEND_CONTEXT_REGS + PT_S9)(a0)
+ REG_L s10, (SUSPEND_CONTEXT_REGS + PT_S10)(a0)
+ REG_L s11, (SUSPEND_CONTEXT_REGS + PT_S11)(a0)
+
+ /* Return zero value */
+ add a0, zero, zero
+
+ /* Return to C code */
+ ret
+END(__cpu_resume_enter)
--
2.25.1
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