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SubjectRe: [PATCH v9 09/17] arm: tegra20: cpuidle: Handle case where secondary CPU hangs on entering LP2
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Hello Daniel,

21.02.2020 18:43, Daniel Lezcano пишет:
> 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@nvidia.com>
>> Tested-by: Peter Geis <pgwipeout@gmail.com>
>> Tested-by: Jasper Korten <jja2000@gmail.com>
>> Tested-by: David Heidelberg <david@ixit.cz>
>> Signed-off-by: Dmitry Osipenko <digetx@gmail.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.

Could you please explain what benefits jiffies have over the ktime_get()?

>> +
>> + /*
>> + * 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.
But udelay() also results into CPU spinning in a busy-loop, and thus,
what's the difference?

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