[PATCH v12 07/10] qcom: cpuidle: Add cpuidle driver for QCOM cpus

Lina Iyer lina.iyer at linaro.org
Mon Dec 1 11:00:22 PST 2014

On Thu, Nov 27 2014 at 01:55 -0700, Daniel Lezcano wrote:
>On 11/27/2014 01:13 AM, Lina Iyer wrote:
>>Add cpuidle driver interface to allow cpus to go into idle states. Use
>>the cpuidle DT interface, common across ARM architectures, to provide
>>the idle state information to the cpuidle framework.
>>Supported modes at this time are Standby and Standalone Power Collapse.
>>Signed-off-by: Lina Iyer <lina.iyer at linaro.org>
>>Acked-by: Daniel Lezcano <daniel.lezcano at linaro.org>
>>Acked-by: Lorenzo Pieralisi <lorenzo.pieralisi at arm.com>
>>  .../bindings/arm/msm/qcom,idle-state.txt           | 81 ++++++++++++++++++++++
>>  drivers/cpuidle/Kconfig.arm                        |  7 ++
>>  drivers/cpuidle/Makefile                           |  1 +
>>  drivers/cpuidle/cpuidle-qcom.c                     | 78 +++++++++++++++++++++
>>  4 files changed, 167 insertions(+)
>>  create mode 100644 Documentation/devicetree/bindings/arm/msm/qcom,idle-state.txt
>>  create mode 100644 drivers/cpuidle/cpuidle-qcom.c
>>diff --git a/Documentation/devicetree/bindings/arm/msm/qcom,idle-state.txt b/Documentation/devicetree/bindings/arm/msm/qcom,idle-state.txt
>>new file mode 100644
>>index 0000000..ae1b07f
>>--- /dev/null
>>+++ b/Documentation/devicetree/bindings/arm/msm/qcom,idle-state.txt
>>@@ -0,0 +1,81 @@
>>+QCOM Idle States for cpuidle driver
>>+ARM provides idle-state node to define the cpuidle states, as defined in [1].
>>+cpuidle-qcom is the cpuidle driver for Qualcomm SoCs and uses these idle
>>+states. Idle states have different enter/exit latency and residency values.
>>+The idle states supported by the QCOM SoC are defined as -
>>+    * Standby
>>+    * Retention
>>+    * Standalone Power Collapse (Standalone PC or SPC)
>>+    * Power Collapse (PC)
>>+Standby: Standby does a little more in addition to architectural clock gating.
>>+When the WFI instruction is executed the ARM core would gate its internal
>>+clocks. In addition to gating the clocks, QCOM cpus use this instruction as a
>>+trigger to execute the SPM state machine. The SPM state machine waits for the
>>+interrupt to trigger the core back in to active. This triggers the cache
>>+hierarchy to enter standby states, when all cpus are idle. An interrupt brings
>>+the SPM state machine out of its wait, the next step is to ensure that the
>>+cache hierarchy is also out of standby, and then the cpu is allowed to resume
>>+Retention: Retention is a low power state where the core is clock gated and
>>+the memory and the registers associated with the core are retained. The
>>+voltage may be reduced to the minimum value needed to keep the processor
>>+registers active. The SPM should be configured to execute the retention
>>+sequence and would wait for interrupt, before restoring the cpu to execution
>>+state. Retention may have a slightly higher latency than Standby.
>>+Standalone PC: A cpu can power down and warmboot if there is a sufficient time
>>+between the time it enters idle and the next known wake up. SPC mode is used
>>+to indicate a core entering a power down state without consulting any other
>>+cpu or the system resources. This helps save power only on that core.  The SPM
>>+sequence for this idle state is programmed to power down the supply to the
>>+core, wait for the interrupt, restore power to the core, and ensure the
>>+system state including cache hierarchy is ready before allowing core to
>>+resume. Applying power and resetting the core causes the core to warmboot
>>+back into Elevation Level (EL) which trampolines the control back to the
>>+kernel. Entering a power down state for the cpu, needs to be done by trapping
>>+into a EL. Failing to do so, would result in a crash enforced by the warm boot
>>+code in the EL for the SoC. On SoCs with write-back L1 cache, the cache has to
>>+be flushed in s/w, before powering down the core.
>>+Power Collapse: This state is similar to the SPC mode, but distinguishes
>>+itself in that the cpu acknowledges and permits the SoC to enter deeper sleep
>>+modes. In a hierarchical power domain SoC, this means L2 and other caches can
>>+be flushed, system bus, clocks - lowered, and SoC main XO clock gated and
>>+voltages reduced, provided all cpus enter this state.  Since the span of low
>>+power modes possible at this state is vast, the exit latency and the residency
>>+of this low power mode would be considered high even though at a cpu level,
>>+this essentially is cpu power down. The SPM in this state also may handshake
>>+with the Resource power manager processor in the SoC to indicate a complete
>>+application processor subsystem shut down.
>>+The idle-state for QCOM SoCs are distinguished by the compatible property of
>>+the idle-states device node.
>>+The devicetree representation of the idle state should be -
>>+Required properties:
>>+- compatible: Must be one of -
>>+			"qcom,idle-state-stby",
>>+			"qcom,idle-state-ret",
>>+			"qcom,idle-state-spc",
>>+			"qcom,idle-state-pc",
>>+		and "arm,idle-state".
>>+Other required and optional properties are specified in [1].
>>+	idle-states {
>>+		CPU_SPC: spc {
>>+			compatible = "qcom,idle-state-spc", "arm,idle-state";
>>+			entry-latency-us = <150>;
>>+			exit-latency-us = <200>;
>>+			min-residency-us = <2000>;
>>+		};
>>+	};
>>+[1]. Documentation/devicetree/bindings/arm/idle-states.txt
>>diff --git a/drivers/cpuidle/Kconfig.arm b/drivers/cpuidle/Kconfig.arm
>>index 8c16ab2..e98993c 100644
>>--- a/drivers/cpuidle/Kconfig.arm
>>+++ b/drivers/cpuidle/Kconfig.arm
>>@@ -63,3 +63,10 @@ config ARM_MVEBU_V7_CPUIDLE
>>  	depends on ARCH_MVEBU
>>  	help
>>  	  Select this to enable cpuidle on Armada 370, 38x and XP processors.
>>+	bool "CPU Idle drivers for Qualcomm processors"
>>+	depends on ARCH_QCOM
>>+	select DT_IDLE_STATES
>>+	help
>>+	  Select this to enable cpuidle for QCOM processors
>>diff --git a/drivers/cpuidle/Makefile b/drivers/cpuidle/Makefile
>>index 4d177b9..6c222d5 100644
>>--- a/drivers/cpuidle/Makefile
>>+++ b/drivers/cpuidle/Makefile
>>@@ -17,6 +17,7 @@ obj-$(CONFIG_ARM_ZYNQ_CPUIDLE)		+= cpuidle-zynq.o
>>  obj-$(CONFIG_ARM_U8500_CPUIDLE)         += cpuidle-ux500.o
>>  obj-$(CONFIG_ARM_AT91_CPUIDLE)          += cpuidle-at91.o
>>  obj-$(CONFIG_ARM_EXYNOS_CPUIDLE)        += cpuidle-exynos.o
>>+obj-$(CONFIG_ARM_QCOM_CPUIDLE)		+= cpuidle-qcom.o
>>  ###############################################################################
>>  # MIPS drivers
>>diff --git a/drivers/cpuidle/cpuidle-qcom.c b/drivers/cpuidle/cpuidle-qcom.c
>>new file mode 100644
>>index 0000000..5e54d9d
>>--- /dev/null
>>+++ b/drivers/cpuidle/cpuidle-qcom.c
>>@@ -0,0 +1,78 @@
>>+ * Copyright (c) 2014, Linaro Limited.
>>+ *
>>+ * This program is free software; you can redistribute it and/or modify
>>+ * it under the terms of the GNU General Public License version 2 and
>>+ * only version 2 as published by the Free Software Foundation.
>>+ *
>>+ * This program is distributed in the hope that it will be useful,
>>+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
>>+ * GNU General Public License for more details.
>>+ *
>>+ */
>>+#include <linux/cpuidle.h>
>>+#include <linux/module.h>
>>+#include <linux/platform_device.h>
>>+#include <soc/qcom/pm.h>
>>+#include "dt_idle_states.h"
>>+static struct qcom_cpu_pm_ops *lpm_ops;
>>+static int qcom_cpu_stby(struct cpuidle_device *dev,
>>+				struct cpuidle_driver *drv, int index)
>>+	if (!lpm_ops->standby(NULL))
>>+		return -1;
>>+	return index;
>>+static int qcom_cpu_spc(struct cpuidle_device *dev,
>>+				struct cpuidle_driver *drv, int index)
>>+	if (!lpm_ops->spc(NULL))
>>+		return -1;
>>+	return index;
>Really ? the lpm_ops return NULL on error ?
>ret = lpm_ops->spc(NULL);
>if (ret)
>	return ret;
My sanity test on the device, did not reveal the insanity in my code :(

Sorry, will try to not repeat it.

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