| Message ID | 1407945127-27554-4-git-send-email-lorenzo.pieralisi@arm.com |
|---|---|
| State | New |
| Headers | show |
On Wed, 13 Aug 2014, Lorenzo Pieralisi wrote: > On most common ARM systems, the low-power states a CPU can be put into are > not discoverable in HW and require device tree bindings to describe > power down suspend operations and idle states parameters. > > In order to enable DT based idle states and configure idle drivers, this > patch implements the bulk infrastructure required to parse the device tree > idle states bindings and initialize the corresponding CPUidle driver states > data. > > The parsing API accepts a start index that defines the first idle state > that should be initialized by the parsing code in order to give new and > legacy driver flexibility over which states should be parsed using the > new DT mechanism. > > The idle states list is obtained from the first cpu in the driver > cpumask, which implicitly means the parsing code expects idle states > (and related list of phandles) to be the same for all CPUs in the > CPUidle driver mask. The kernel does not check this assumption, it must > be enforced by the bootloader to ensure correct system behaviour. Can we make the kernel a little less reliant on bootloader to ensure correct system behaviour please? If assumptions are assumed by the kernel, it should at least print a warning and simply ignore the information when such assumption are not respected. > + /* > + * We get the idle states for the first logical cpu in the > + * driver mask. The kernel does not check idle states on all > + * cpus in the driver mask, they are assumed to be the same > + * by default. > + */ What if they're not? Nicolas -- To unsubscribe from this list: send the line "unsubscribe linux-pm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Wed, Aug 13, 2014 at 05:31:11PM +0100, Nicolas Pitre wrote: > On Wed, 13 Aug 2014, Lorenzo Pieralisi wrote: > > > On most common ARM systems, the low-power states a CPU can be put into are > > not discoverable in HW and require device tree bindings to describe > > power down suspend operations and idle states parameters. > > > > In order to enable DT based idle states and configure idle drivers, this > > patch implements the bulk infrastructure required to parse the device tree > > idle states bindings and initialize the corresponding CPUidle driver states > > data. > > > > The parsing API accepts a start index that defines the first idle state > > that should be initialized by the parsing code in order to give new and > > legacy driver flexibility over which states should be parsed using the > > new DT mechanism. > > > > The idle states list is obtained from the first cpu in the driver > > cpumask, which implicitly means the parsing code expects idle states > > (and related list of phandles) to be the same for all CPUs in the > > CPUidle driver mask. The kernel does not check this assumption, it must > > be enforced by the bootloader to ensure correct system behaviour. > > Can we make the kernel a little less reliant on bootloader to ensure > correct system behaviour please? If assumptions are assumed by the > kernel, it should at least print a warning and simply ignore the > information when such assumption are not respected. I think the check adds complexity (it means stashing the idle states phandles for the first cpu, loop through the cpus in the mask and compare the phandles to the ones stashed for the first cpu for all cpus in the driver mask) for not much. I was told that it is not up to the kernel to validate the DT, but if you want I can implement the check even though I really think it is overkill. > > + /* > > + * We get the idle states for the first logical cpu in the > > + * driver mask. The kernel does not check idle states on all > > + * cpus in the driver mask, they are assumed to be the same > > + * by default. > > + */ > > What if they're not? It boils down to detecting what CPUs share the same idle states and initialize dynamically a number of CPU idle drivers accordingly. It is doable on top of this patch which is usable on homogeneous machines as a starting point. I do not think it is a big issue to live with this limitation at the moment, given that it can be augmented when this code gets in the kernel. I did not want to add more complexity to this already complex patch series, that's the reason why I have not implemented the multiple driver (whose first target is obviously bL systems) approach from the beginning, and I think that's reasonable. Thanks, Lorenzo
On Wed, 13 Aug 2014, Lorenzo Pieralisi wrote: > On Wed, Aug 13, 2014 at 05:31:11PM +0100, Nicolas Pitre wrote: > > On Wed, 13 Aug 2014, Lorenzo Pieralisi wrote: > > > > > On most common ARM systems, the low-power states a CPU can be put into are > > > not discoverable in HW and require device tree bindings to describe > > > power down suspend operations and idle states parameters. > > > > > > In order to enable DT based idle states and configure idle drivers, this > > > patch implements the bulk infrastructure required to parse the device tree > > > idle states bindings and initialize the corresponding CPUidle driver states > > > data. > > > > > > The parsing API accepts a start index that defines the first idle state > > > that should be initialized by the parsing code in order to give new and > > > legacy driver flexibility over which states should be parsed using the > > > new DT mechanism. > > > > > > The idle states list is obtained from the first cpu in the driver > > > cpumask, which implicitly means the parsing code expects idle states > > > (and related list of phandles) to be the same for all CPUs in the > > > CPUidle driver mask. The kernel does not check this assumption, it must > > > be enforced by the bootloader to ensure correct system behaviour. > > > > Can we make the kernel a little less reliant on bootloader to ensure > > correct system behaviour please? If assumptions are assumed by the > > kernel, it should at least print a warning and simply ignore the > > information when such assumption are not respected. > > I think the check adds complexity (it means stashing the idle states > phandles for the first cpu, loop through the cpus in the mask and compare > the phandles to the ones stashed for the first cpu for all cpus in the > driver mask) for not much. > > I was told that it is not up to the kernel to validate the DT, but if > you want I can implement the check even though I really think it is > overkill. DT validation is not the same as resiliance against messed-up DT content. If the kernel is going to boot regardless then this is fine. If the kernel is going to crash, or work suboptimally without returning a clue because some implicit assumptions are not respected then this is bad. And people _will_ mess up their DT from time to time. So if you tell me a messed-up DT won't bear much consequences then I'm fine with that. Nicolas
diff --git a/drivers/cpuidle/Kconfig b/drivers/cpuidle/Kconfig index 32748c3..8deb934 100644 --- a/drivers/cpuidle/Kconfig +++ b/drivers/cpuidle/Kconfig @@ -25,6 +25,9 @@ config CPU_IDLE_GOV_MENU bool "Menu governor (for tickless system)" default y +config DT_IDLE_STATES + bool + menu "ARM CPU Idle Drivers" depends on ARM source "drivers/cpuidle/Kconfig.arm" diff --git a/drivers/cpuidle/Makefile b/drivers/cpuidle/Makefile index 11edb31..002b653 100644 --- a/drivers/cpuidle/Makefile +++ b/drivers/cpuidle/Makefile @@ -4,6 +4,7 @@ obj-y += cpuidle.o driver.o governor.o sysfs.o governors/ obj-$(CONFIG_ARCH_NEEDS_CPU_IDLE_COUPLED) += coupled.o +obj-$(CONFIG_DT_IDLE_STATES) += dt_idle_states.o ################################################################################## # ARM SoC drivers diff --git a/drivers/cpuidle/dt_idle_states.c b/drivers/cpuidle/dt_idle_states.c new file mode 100644 index 0000000..207f8f7 --- /dev/null +++ b/drivers/cpuidle/dt_idle_states.c @@ -0,0 +1,140 @@ +/* + * DT idle states parsing code. + * + * Copyright (C) 2014 ARM Ltd. + * Author: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com> + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License version 2 as + * published by the Free Software Foundation. + */ + +#define pr_fmt(fmt) "DT idle-states: " fmt + +#include <linux/cpuidle.h> +#include <linux/cpumask.h> +#include <linux/errno.h> +#include <linux/kernel.h> +#include <linux/module.h> +#include <linux/of.h> +#include <linux/of_device.h> + +#include "dt_idle_states.h" + +static int init_state_node(struct cpuidle_state *idle_state, + struct device_node *state_node) +{ + int err; + + err = of_property_read_u32(state_node, "wakeup-latency-us", + &idle_state->exit_latency); + if (err) { + u32 entry_latency, exit_latency; + + err = of_property_read_u32(state_node, "entry-latency-us", + &entry_latency); + if (err) { + pr_debug(" * %s missing entry-latency-us property\n", + state_node->full_name); + return -EINVAL; + } + + err = of_property_read_u32(state_node, "exit-latency-us", + &exit_latency); + if (err) { + pr_debug(" * %s missing exit-latency-us property\n", + state_node->full_name); + return -EINVAL; + } + /* + * If wakeup-latency-us is missing, default to entry+exit + * latencies as defined in idle states bindings + */ + idle_state->exit_latency = entry_latency + exit_latency; + } + + err = of_property_read_u32(state_node, "min-residency-us", + &idle_state->target_residency); + if (err) { + pr_debug(" * %s missing min-residency-us property\n", + state_node->full_name); + return -EINVAL; + } + + idle_state->flags = CPUIDLE_FLAG_TIME_VALID; + if (of_property_read_bool(state_node, "local-timer-stop")) + idle_state->flags |= CPUIDLE_FLAG_TIMER_STOP; + /* + * TODO: + * replace with kstrdup and pointer assignment when name + * and desc become string pointers + */ + strncpy(idle_state->name, state_node->name, CPUIDLE_NAME_LEN - 1); + strncpy(idle_state->desc, state_node->name, CPUIDLE_DESC_LEN - 1); + return 0; +} + +/** + * dt_init_idle_driver() - Parse the DT idle states and initialize the + * idle driver states array + * @drv: Pointer to CPU idle driver to be initialized + * @start_idx: First idle state index to be initialized + * + * If DT idle states are detected and are valid the state count and states + * array entries in the cpuidle driver are initialized accordingly starting + * from index start_idx. + * + * Return: number of valid DT idle states parsed, <0 on failure + */ +int dt_init_idle_driver(struct cpuidle_driver *drv, unsigned int start_idx) +{ + struct cpuidle_state *idle_state; + struct device_node *state_node, *cpu_node; + int i; + unsigned int state_idx = start_idx; + + if (state_idx >= CPUIDLE_STATE_MAX) + return -EINVAL; + /* + * We get the idle states for the first logical cpu in the + * driver mask. The kernel does not check idle states on all + * cpus in the driver mask, they are assumed to be the same + * by default. + */ + cpu_node = of_cpu_device_node_get(cpumask_first(drv->cpumask)); + + for (i = 0; ; i++) { + int err; + + state_node = of_parse_phandle(cpu_node, "cpu-idle-states", i); + if (!state_node) + break; + + if (state_idx == CPUIDLE_STATE_MAX) { + pr_warn("State index reached static CPU idle driver states array size\n"); + break; + } + + idle_state = &drv->states[state_idx++]; + err = init_state_node(idle_state, state_node); + if (err) { + pr_err("Parsing idle state node %s failed with err %d\n", + state_node->full_name, err); + return err; + } + } + /* + * Update the driver state count only if some valid DT idle states + * were detected + */ + if (i) + drv->state_count = state_idx; + + /* + * Return the number of present and valid DT idle states, which can + * also be 0 on platforms with missing DT idle states or legacy DT + * configuration predating the DT idle states bindings. + */ + return i; +} +EXPORT_SYMBOL_GPL(dt_init_idle_driver); diff --git a/drivers/cpuidle/dt_idle_states.h b/drivers/cpuidle/dt_idle_states.h new file mode 100644 index 0000000..728c37c --- /dev/null +++ b/drivers/cpuidle/dt_idle_states.h @@ -0,0 +1,5 @@ +#ifndef __DT_IDLE_STATES +#define __DT_IDLE_STATES + +int dt_init_idle_driver(struct cpuidle_driver *drv, unsigned int start_idx); +#endif
On most common ARM systems, the low-power states a CPU can be put into are not discoverable in HW and require device tree bindings to describe power down suspend operations and idle states parameters. In order to enable DT based idle states and configure idle drivers, this patch implements the bulk infrastructure required to parse the device tree idle states bindings and initialize the corresponding CPUidle driver states data. The parsing API accepts a start index that defines the first idle state that should be initialized by the parsing code in order to give new and legacy driver flexibility over which states should be parsed using the new DT mechanism. The idle states list is obtained from the first cpu in the driver cpumask, which implicitly means the parsing code expects idle states (and related list of phandles) to be the same for all CPUs in the CPUidle driver mask. The kernel does not check this assumption, it must be enforced by the bootloader to ensure correct system behaviour. Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com> --- drivers/cpuidle/Kconfig | 3 + drivers/cpuidle/Makefile | 1 + drivers/cpuidle/dt_idle_states.c | 140 +++++++++++++++++++++++++++++++++++++++ drivers/cpuidle/dt_idle_states.h | 5 ++ 4 files changed, 149 insertions(+) create mode 100644 drivers/cpuidle/dt_idle_states.c create mode 100644 drivers/cpuidle/dt_idle_states.h