linux-kernel - Re: [PATCH v9 09/17] arm: tegra20: cpuidle: Handle case where secondary CPU hangs on entering LP2

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Message-ID: <20200221154318.GO10516@linaro.org>
Date:   Fri, 21 Feb 2020 16:43:18 +0100
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     Dmitry Osipenko <digetx@...il.com>
Cc:     Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Peter De Schrijver <pdeschrijver@...dia.com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Michał Mirosław <mirq-linux@...e.qmqm.pl>,
        Jasper Korten <jja2000@...il.com>,
        David Heidelberg <david@...t.cz>,
        Peter Geis <pgwipeout@...il.com>, linux-pm@...r.kernel.org,
        linux-tegra@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v9 09/17] arm: tegra20: cpuidle: Handle case where
 secondary CPU hangs on entering LP2

On Thu, Feb 13, 2020 at 02:51:26AM +0300, Dmitry Osipenko wrote:
> It is possible that something may go wrong with the secondary CPU, in that
> case it is much nicer to get a dump of the flow-controller state before
> hanging machine.
> 
> Acked-by: Peter De Schrijver <pdeschrijver@...dia.com>
> Tested-by: Peter Geis <pgwipeout@...il.com>
> Tested-by: Jasper Korten <jja2000@...il.com>
> Tested-by: David Heidelberg <david@...t.cz>
> Signed-off-by: Dmitry Osipenko <digetx@...il.com>
> ---
>  arch/arm/mach-tegra/cpuidle-tegra20.c | 47 +++++++++++++++++++++++++--
>  1 file changed, 45 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/arm/mach-tegra/cpuidle-tegra20.c b/arch/arm/mach-tegra/cpuidle-tegra20.c
> index 9672c619f4bc..bcc158b72e67 100644
> --- a/arch/arm/mach-tegra/cpuidle-tegra20.c
> +++ b/arch/arm/mach-tegra/cpuidle-tegra20.c
> @@ -83,14 +83,57 @@ static inline void tegra20_wake_cpu1_from_reset(void)
>  }
>  #endif
>  
> +static void tegra20_report_cpus_state(void)
> +{
> +	unsigned long cpu, lcpu, csr;
> +
> +	for_each_cpu(lcpu, cpu_possible_mask) {
> +		cpu = cpu_logical_map(lcpu);
> +		csr = flowctrl_read_cpu_csr(cpu);
> +
> +		pr_err("cpu%lu: online=%d flowctrl_csr=0x%08lx\n",
> +		       cpu, cpu_online(lcpu), csr);
> +	}
> +}
> +
> +static int tegra20_wait_for_secondary_cpu_parking(void)
> +{
> +	unsigned int retries = 3;
> +
> +	while (retries--) {
> +		ktime_t timeout = ktime_add_ms(ktime_get(), 500);

Oops I missed this one. Do not use ktime_get() in this code path, use jiffies.

> +
> +		/*
> +		 * The primary CPU0 core shall wait for the secondaries
> +		 * shutdown in order to power-off CPU's cluster safely.
> +		 * The timeout value depends on the current CPU frequency,
> +		 * it takes about 40-150us  in average and over 1000us in
> +		 * a worst case scenario.
> +		 */
> +		do {
> +			if (tegra_cpu_rail_off_ready())
> +				return 0;
> +
> +		} while (ktime_before(ktime_get(), timeout));

So this loop will aggresively call tegra_cpu_rail_off_ready() and retry 3
times. The tegra_cpu_rail_off_ready() function can be called thoushand of times
here but the function will hang 1.5s :/

I suggest something like:

	while (retries--i && !tegra_cpu_rail_off_ready()) 
		udelay(100);

So <retries> calls to tegra_cpu_rail_off_ready() and 100us x <retries> maximum
impact.

> +		pr_err("secondary CPU taking too long to park\n");
> +
> +		tegra20_report_cpus_state();
> +	}
> +
> +	pr_err("timed out waiting secondaries to park\n");
> +
> +	return -ETIMEDOUT;
> +}
> +
>  static bool tegra20_cpu_cluster_power_down(struct cpuidle_device *dev,
>  					   struct cpuidle_driver *drv,
>  					   int index)
>  {
>  	bool ret;
>  
> -	while (!tegra_cpu_rail_off_ready())
> -		cpu_relax();
> +	if (tegra20_wait_for_secondary_cpu_parking())
> +		return false;
>  
>  	ret = !tegra_pm_enter_lp2();
>  
> -- 
> 2.24.0
> 

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