Re: [PATCH] cpuidle: JZ4780: Add Ingenic JZ4780 cpuidle driver.

[Paul Cercueil]

Hi Zhou,

Le sam., juil. 24 2021 at 17:19:59 +0800, 周琰杰 (Zhou Yanjie) 
<zhouyanjie@xxxxxxxxxxxxxx> a écrit :
> The JZ4780 has a high overhead to executing a MIPS wait on SMP, as a
> core must flush out dirty cache lines from its data cache before doing
> so. This is because the core clock is gated during a wait and if the
> other core tries to access a dirty line from the waiting core's cache,
> it will lock up.
>
> To mitigate some of this impact, this driver provides a simple polling
> top level idle state, to try to avoid the cache flushing overhead when
> the wait will only be short. The second level state is implemented 
> with
> the MIPS wait instruction.
>
> This patch first found in the github repository of CI20, the original
> author is Alex Smith. Because there is a chance to cause kernel hang
> scenarios which can occur within hours or even within days, so this
> patch was abandoned, but now it is determined that this is not the
> problem caused by this patch, but caused by the cache driver. With
> the new Ingenic specific cache driver, it has been working properly
> on CI20 v1 for more than one week.
>
> Tested-by: H. Nikolaus Schaller <hns@xxxxxxxxxxxxx>
> Signed-off-by: Alex Smith <alex.smith@xxxxxxxxxx>
> Signed-off-by: 周琰杰 (Zhou Yanjie) <zhouyanjie@xxxxxxxxxxxxxx>
> ---
>  drivers/cpuidle/Kconfig.mips     |  8 +++++
>  drivers/cpuidle/Makefile         |  1 +
>  drivers/cpuidle/cpuidle-jz4780.c | 74 
> ++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 83 insertions(+)
>  create mode 100644 drivers/cpuidle/cpuidle-jz4780.c
>
> diff --git a/drivers/cpuidle/Kconfig.mips 
> b/drivers/cpuidle/Kconfig.mips
> index c3c011a..4a55d24 100644
> --- a/drivers/cpuidle/Kconfig.mips
> +++ b/drivers/cpuidle/Kconfig.mips
> @@ -16,3 +16,11 @@ config MIPS_CPS_CPUIDLE
>  	  Processing System (CPS) architecture. In order to make use of
>  	  the deepest idle states you will need to ensure that you are
>  	  also using the CONFIG_MIPS_CPS SMP implementation.
> +
> +config MIPS_JZ4780_CPUIDLE
> +	bool "CPU Idle driver for Ingenic JZ4780"
> +	depends on MACH_JZ4780 && SMP
> +	default y
> +	help
> +	  Select this option to enable CPU idle state management through
> +	  cpuidle for Ingenic JZ4780 platforms.
> diff --git a/drivers/cpuidle/Makefile b/drivers/cpuidle/Makefile
> index 26bbc5e..1dd372f 100644
> --- a/drivers/cpuidle/Makefile
> +++ b/drivers/cpuidle/Makefile
> @@ -29,6 +29,7 @@ obj-$(CONFIG_ARM_QCOM_SPM_CPUIDLE)	+= 
> cpuidle-qcom-spm.o
>  
> ###############################################################################
>  # MIPS drivers
>  obj-$(CONFIG_MIPS_CPS_CPUIDLE)		+= cpuidle-cps.o
> +obj-$(CONFIG_MIPS_JZ4780_CPUIDLE)	+= cpuidle-jz4780.o
>
>  
> ###############################################################################
>  # POWERPC drivers
> diff --git a/drivers/cpuidle/cpuidle-jz4780.c 
> b/drivers/cpuidle/cpuidle-jz4780.c
> new file mode 100644
> index 00000000..2025de4
> --- /dev/null
> +++ b/drivers/cpuidle/cpuidle-jz4780.c
> @@ -0,0 +1,74 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * JZ4780 CPU idle driver
> + * Copyright (C) 2015 Imagination Technologies
> + * Author: Alex Smith <alex.smith@xxxxxxxxxx>
> + * Copyright (c) 2020 周琰杰 (Zhou Yanjie) 
> <zhouyanjie@xxxxxxxxxxxxxx>
> + */
> +
> +#include <linux/cpuidle.h>
> +#include <linux/init.h>
> +#include <linux/sched.h>
> +#include <linux/sched/idle.h>
> +
> +#include <asm/idle.h>
> +#include <asm/mipsregs.h>
> +
> +/*
> + * The JZ4780 has a high overhead to entering just the basic MIPS 
> wait on SMP,
> + * due to the requirement to flush out dirty lines from the dcache 
> before
> + * waiting. Therefore, we try to mitigate this overhead by using a 
> simple
> + * polling loop for short waits.
> + */
> +static int jz4780_cpuidle_poll_enter(struct cpuidle_device *dev,
> +				     struct cpuidle_driver *drv, int index)
> +{
> +	if (!current_set_polling_and_test())
> +		while (!need_resched() && !(read_c0_cause() & read_c0_status() & 
> CAUSEF_IP))
> +			cpu_relax();
> +
> +	current_clr_polling();
> +	local_irq_enable();
> +
> +	return index;
> +}
> +
> +static struct cpuidle_driver jz4780_cpuidle_driver = {
> +	.name = "jz4780_cpuidle",
> +	.owner = THIS_MODULE,
> +	.states = {
> +		{
> +			.enter = jz4780_cpuidle_poll_enter,
> +			.exit_latency = 1,
> +			.target_residency = 1,
> +			.power_usage = UINT_MAX,
> +			.name = "poll",
> +			.desc = "polling loop",
> +		},
> +		{
> +			.enter = mips_cpuidle_wait_enter,
> +			.exit_latency = 50,
> +			.target_residency = 300,
> +			.power_usage = UINT_MAX,
> +			.name = "wait",
> +			.desc = "MIPS wait",
> +		},
> +	},
> +	.state_count = 2,
> +};
> +
> +static int __init jz4780_cpuidle_init(void)
> +{
> +	int ret;
> +
> +	ret = cpuidle_register(&jz4780_cpuidle_driver, NULL);

You're missing something here - you never check that the kernel is 
actually running on a JZ4780.

Cheers,
-Paul

> +	if (ret) {
> +		pr_err("Failed to register JZ4780 idle driver: %d\n", ret);
> +		return ret;
> +	}
> +
> +	pr_info("JZ4780 idle driver registered\n");
> +
> +	return 0;
> +}
> +device_initcall(jz4780_cpuidle_init);
> --
> 2.7.4