Subject: [PATCH v2 10/10] arm: zynq: Add cpuidle support

From: [email-masked] (Daniel Lezcano)
Date: Wed, 27 Mar 2013 11:07:16 +0100

On 03/26/2013 06:43 PM, Michal Simek wrote:
> Add support for cpuidle.
> 
> Signed-off-by: Michal Simek <[email-masked]>

Hi Michal,

at the first glance, the driver won't enter in the self refresh state.

If I am right, by checking:

/sys/devices/system/cpu/cpu0/cpuidle/state1/usage, it should be always zero.

Also, I see there is self refresh but you save the cpu context, so it is
cpu shutdown no ?

In this case, 3 states would be needed, WFI, self-refresh, powerdown, no ?

The comments below applies for this driver based on linux-pm-next.

https://git.kernel.org/cgit/linux/kernel/git/rafael/linux-pm.git/

> ---
> v2: Fix file header
> ---
>  arch/arm/mach-zynq/Makefile  |    1 +
>  arch/arm/mach-zynq/cpuidle.c |  133 ++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 134 insertions(+)
>  create mode 100644 arch/arm/mach-zynq/cpuidle.c
> 
> diff --git a/arch/arm/mach-zynq/Makefile b/arch/arm/mach-zynq/Makefile
> index 1b25d92..238b8f9 100644
> --- a/arch/arm/mach-zynq/Makefile
> +++ b/arch/arm/mach-zynq/Makefile
> @@ -7,4 +7,5 @@ obj-y				:= common.o slcr.o
>  CFLAGS_REMOVE_hotplug.o		=-march=armv6k
>  CFLAGS_hotplug.o 		=-Wa,-march=armv7-a -mcpu=cortex-a9
>  obj-$(CONFIG_HOTPLUG_CPU)	+= hotplug.o
> +obj-$(CONFIG_CPU_IDLE) 		+= cpuidle.o
>  obj-$(CONFIG_SMP)		+= headsmp.o platsmp.o
> diff --git a/arch/arm/mach-zynq/cpuidle.c b/arch/arm/mach-zynq/cpuidle.c
> new file mode 100644
> index 0000000..4ed8855
> --- /dev/null
> +++ b/arch/arm/mach-zynq/cpuidle.c
> @@ -0,0 +1,133 @@
> +/*
> + * Copyright (C) 2012-2013 Xilinx
> + *
> + * CPU idle support for Xilinx
> + *
> + * based on arch/arm/mach-at91/cpuidle.c
> + *
> + * This file is licensed under the terms of the GNU General Public
> + * License version 2.  This program is licensed "as is" without any
> + * warranty of any kind, whether express or implied.
> + *
> + * The cpu idle uses wait-for-interrupt and RAM self refresh in order
> + * to implement two idle states -
> + * #1 wait-for-interrupt
> + * #2 wait-for-interrupt and RAM self refresh
> + *
> + * Note that this code is only intended as a prototype and is not tested
> + * well yet, or tuned for the Xilinx Cortex A9. Also note that for a
> + * tickless kernel, high res timers must not be turned on. The cpuidle
> + * framework must also be turned on in the kernel.
> + */
> +
> +#include <linux/kernel.h>
> +#include <linux/init.h>
> +#include <linux/platform_device.h>
> +#include <linux/cpuidle.h>
> +#include <linux/io.h>
> +#include <linux/export.h>
> +#include <linux/clockchips.h>
> +#include <linux/cpu_pm.h>
> +#include <linux/clk.h>
> +#include <linux/err.h>
> +#include <asm/proc-fns.h>
> +
> +#define XILINX_MAX_STATES	1

You defined XILINX_MAX_STATES as 1, it should be 2.

> +static DEFINE_PER_CPU(struct cpuidle_device, xilinx_cpuidle_device);
> +
> +/* Actual code that puts the SoC in different idle states */
> +static int xilinx_enter_idle(struct cpuidle_device *dev,
> +		struct cpuidle_driver *drv, int index)
> +{
> +	struct timeval before, after;
> +	int idle_time;
> +
> +	local_irq_disable();

Remove this line, it is done by the caller.

> +	do_gettimeofday(&before);

Remove this line, that will be taken into account by the driver's
en_core_tk_irqen flag.

> +
> +	if (index == 0)
> +		/* Wait for interrupt state */
> +		cpu_do_idle();

Don't check the index, see in the driver initialization comment below
the defaul wfi state. You will have one state entering WFI and the
xilinx_enter_idle function entering with always index 1.

> +	else if (index == 1) {
> +		unsigned int cpu_id = smp_processor_id();
> +
> +		clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_ENTER, &cpu_id);

Remove this line, CPUIDLE_FLAG_TIMER_STOP will tell the cpuidle
framework to handle that.

> +		/* Devices must be stopped here */
> +		cpu_pm_enter();
> +
> +		/* Add code for DDR self refresh start */
> +
> +		cpu_do_idle();
> +		/*cpu_suspend(foo, bar);*/
> +
> +		/* Add code for DDR self refresh stop */
> +
> +		cpu_pm_exit();
> +
> +		clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_EXIT, &cpu_id);

Remove this line, CPUIDLE_FLAG_TIMER_STOP will tell the cpuidle
framework to handle that.

> +	}
> +
> +	do_gettimeofday(&after);
> +	local_irq_enable();
> +	idle_time = (after.tv_sec - before.tv_sec) * USEC_PER_SEC +
> +			(after.tv_usec - before.tv_usec);
> +
> +	dev->last_residency = idle_time;

Remove these lines about time computation, that is handled by the caller.

> +	return index;
> +}
> +
> +static struct cpuidle_driver xilinx_idle_driver = {
> +	.name = "xilinx_idle",
> +	.owner = THIS_MODULE,
> +	.state_count = XILINX_MAX_STATES,
> +	/* Wait for interrupt state */
> +	.states[0] = {
> +		.enter = xilinx_enter_idle,
> +		.exit_latency = 1,
> +		.target_residency = 10000,
> +		.flags = CPUIDLE_FLAG_TIME_VALID,
> +		.name = "WFI",
> +		.desc = "Wait for interrupt",
> +	},
> +	/* Wait for interrupt and RAM self refresh state */
> +	.states[1] = {
> +		.enter = xilinx_enter_idle,
> +		.exit_latency = 10,
> +		.target_residency = 10000,
> +		.flags = CPUIDLE_FLAG_TIME_VALID,
> +		.name = "RAM_SR",
> +		.desc = "WFI and RAM Self Refresh",
> +	},
> +};

static struct cpuidle_driver xilinx_idle_driver = {
	.name = "xilinx_idle",
	.owner = THIS_MODULE,
        .states = {
                ARM_CPUIDLE_WFI_STATE,
                {
                        .enter            = xilinx_enter_idle,
                        .exit_latency     = 10,
                        .target_residency = 10000,
                        .flags            = CPUIDLE_FLAG_TIME_VALID,
                                            CPUIDLE_FLAG_TIMER_STOP,
                        .name             = "RAM_SR",
                        .desc             = "WFI and RAM Self Refresh",
                },
        },
        .safe_state_index = 0,
	.state_count = XILINX_MAX_STATES,
};

> +/* Initialize CPU idle by registering the idle states */
> +static int xilinx_init_cpuidle(void)
> +{
> +	unsigned int cpu;
> +	struct cpuidle_device *device;
> +	int ret;
> +
> +	ret = cpuidle_register_driver(&xilinx_idle_driver);
> +	if (ret) {
> +		pr_err("Registering Xilinx CpuIdle Driver failed.\n");
> +		return ret;
> +	}
> +
> +	for_each_possible_cpu(cpu) {
> +		device = &per_cpu(xilinx_cpuidle_device, cpu);
> +		device->state_count = XILINX_MAX_STATES;

This is initialization is done from the cpuidle_register_device. As
drv->state_count == device->state_count.

> +		device->cpu = cpu;
> +		ret = cpuidle_register_device(device);
> +		if (ret) {
> +			pr_err("xilinx_init_cpuidle: Failed registering\n");
> +			return ret;
> +		}
> +	}
> +
> +	pr_info("Xilinx CpuIdle Driver started\n");
> +	return 0;
> +}
> +device_initcall(xilinx_init_cpuidle);
> 

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