ACPI: RISC-V: Add LPI driver

Enable Low Power Idle (LPI) based cpuidle driver for RISC-V platforms.
It depends on SBI HSM calls for idle state transitions.

Signed-off-by: Sunil V L <[e-mail]>
Reviewed-by: Andrew Jones <[e-mail]>
Acked-by: Rafael J. Wysocki <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Palmer Dabbelt <[e-mail]>

drivers/acpi/riscv/Makefile

···
 # SPDX-License-Identifier: GPL-2.0-only
-obj-y 	+= rhct.o
+obj-y					+= rhct.o
+obj-$(CONFIG_ACPI_PROCESSOR_IDLE)	+= cpuidle.o

drivers/acpi/riscv/cpuidle.c

···
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2024, Ventana Micro Systems Inc
+ *	Author: Sunil V L <[e-mail]>
+ *
+ */
+
+#include <linux/acpi.h>
+#include <acpi/processor.h>
+#include <linux/cpu_pm.h>
+#include <linux/cpuidle.h>
+#include <linux/suspend.h>
+#include <asm/cpuidle.h>
+#include <asm/sbi.h>
+#include <asm/suspend.h>
+
+#define RISCV_FFH_LPI_TYPE_MASK	GENMASK_ULL(63, 60)
+#define RISCV_FFH_LPI_RSVD_MASK	GENMASK_ULL(59, 32)
+
+#define RISCV_FFH_LPI_TYPE_SBI	BIT_ULL(60)
+
+static int acpi_cpu_init_idle(unsigned int cpu)
+{
+	int i;
+	struct acpi_lpi_state *lpi;
+	struct acpi_processor *pr = per_cpu(processors, cpu);
+
+	if (unlikely(!pr || !pr->flags.has_lpi))
+		return -EINVAL;
+
+	if (!riscv_sbi_hsm_is_supported())
+		return -ENODEV;
+
+	if (pr->power.count <= 1)
+		return -ENODEV;
+
+	for (i = 1; i < pr->power.count; i++) {
+		u32 state;
+
+		lpi = &pr->power.lpi_states[i];
+
+		/*
+		 * Validate Entry Method as per FFH spec.
+		 * bits[63:60] should be 0x1
+		 * bits[59:32] should be 0x0
+		 * bits[31:0] represent a SBI power_state
+		 */
+		if (((lpi->address & RISCV_FFH_LPI_TYPE_MASK) != RISCV_FFH_LPI_TYPE_SBI) ||
+		    (lpi->address & RISCV_FFH_LPI_RSVD_MASK)) {
+			pr_warn("Invalid LPI entry method %#llx\n", lpi->address);
+			return -EINVAL;
+		}
+
+		state = lpi->address;
+		if (!riscv_sbi_suspend_state_is_valid(state)) {
+			pr_warn("Invalid SBI power state %#x\n", state);
+			return -EINVAL;
+		}
+	}
+
+	return 0;
+}
+
+int acpi_processor_ffh_lpi_probe(unsigned int cpu)
+{
+	return acpi_cpu_init_idle(cpu);
+}
+
+int acpi_processor_ffh_lpi_enter(struct acpi_lpi_state *lpi)
+{
+	u32 state = lpi->address;
+
+	if (state & SBI_HSM_SUSP_NON_RET_BIT)
+		return CPU_PM_CPU_IDLE_ENTER_PARAM(riscv_sbi_hart_suspend,
+						   lpi->index,
+						   state);
+	else
+		return CPU_PM_CPU_IDLE_ENTER_RETENTION_PARAM(riscv_sbi_hart_suspend,
+							     lpi->index,
+							     state);
+}