linux-kernel - Re: [PATCH v9 09/26] arm64: Unmask PMR before going idle

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Message-ID: <6d9cd0ea-d487-bfb0-0461-1e0fcd24a7e1@arm.com>
Date:   Wed, 23 Jan 2019 08:56:20 +0000
From:   Julien Thierry <julien.thierry@....com>
To:     Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc:     linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        Mark Rutland <mark.rutland@....com>,
        Daniel Thompson <daniel.thompson@...aro.org>,
        Marc Zyngier <marc.zyngier@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Christoffer Dall <christoffer.dall@....com>,
        James Morse <james.morse@....com>,
        Joel Fernandes <joel@...lfernandes.org>
Subject: Re: [PATCH v9 09/26] arm64: Unmask PMR before going idle

On 22/01/2019 20:18, Ard Biesheuvel wrote:
> On Mon, 21 Jan 2019 at 16:36, Julien Thierry <julien.thierry@....com> wrote:
>>
>> CPU does not received signals for interrupts with a priority masked by
>> ICC_PMR_EL1. This means the CPU might not come back from a WFI
>> instruction.
>>
>> Make sure ICC_PMR_EL1 does not mask interrupts when doing a WFI.
>>
>> Since the logic of cpu_do_idle is becoming a bit more complex than just
>> two instructions, lets turn it from ASM to C.
>>
>> Signed-off-by: Julien Thierry <julien.thierry@....com>
>> Suggested-by: Daniel Thompson <daniel.thompson@...aro.org>
>> Cc: Catalin Marinas <catalin.marinas@....com>
>> Cc: Will Deacon <will.deacon@....com>
>> ---
>>  arch/arm64/kernel/process.c | 45 +++++++++++++++++++++++++++++++++++++++++++++
>>  arch/arm64/mm/proc.S        | 11 -----------
>>  2 files changed, 45 insertions(+), 11 deletions(-)
>>
>> diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
>> index 6d410fc..f05b63f 100644
>> --- a/arch/arm64/kernel/process.c
>> +++ b/arch/arm64/kernel/process.c
>> @@ -51,6 +51,7 @@
>>  #include <linux/thread_info.h>
>>
>>  #include <asm/alternative.h>
>> +#include <asm/arch_gicv3.h>
>>  #include <asm/compat.h>
>>  #include <asm/cacheflush.h>
>>  #include <asm/exec.h>
>> @@ -74,6 +75,50 @@
>>
>>  void (*arm_pm_restart)(enum reboot_mode reboot_mode, const char *cmd);
>>
>> +static inline void __cpu_do_idle(void)
>> +{
>> +       dsb(sy);
>> +       wfi();
>> +}
>> +
>> +static inline void __cpu_do_idle_irqprio(void)
> 
> Can we drop the 'inline's from all the function definitions in .c
> files? (not just in this patch)
> We tend to leave that to the compiler.
> 

Sure, I guess cpu_do_idle() isn't a performance critical path anyway.

Unless anyone argues against it, I'll drop these inlines for the next
version.

Thanks,

Julien

>> +{
>> +       unsigned long pmr;
>> +       unsigned long daif_bits;
>> +
>> +       daif_bits = read_sysreg(daif);
>> +       write_sysreg(daif_bits | PSR_I_BIT, daif);
>> +
>> +       /*
>> +        * Unmask PMR before going idle to make sure interrupts can
>> +        * be raised.
>> +        */
>> +       pmr = gic_read_pmr();
>> +       gic_write_pmr(GIC_PRIO_IRQON);
>> +
>> +       __cpu_do_idle();
>> +
>> +       gic_write_pmr(pmr);
>> +       write_sysreg(daif_bits, daif);
>> +}
>> +
>> +/*
>> + *     cpu_do_idle()
>> + *
>> + *     Idle the processor (wait for interrupt).
>> + *
>> + *     If the CPU supports priority masking we must do additional work to
>> + *     ensure that interrupts are not masked at the PMR (because the core will
>> + *     not wake up if we block the wake up signal in the interrupt controller).
>> + */
>> +void cpu_do_idle(void)
>> +{
>> +       if (system_uses_irq_prio_masking())
>> +               __cpu_do_idle_irqprio();
>> +       else
>> +               __cpu_do_idle();
>> +}
>> +
>>  /*
>>   * This is our default idle handler.
>>   */
>> diff --git a/arch/arm64/mm/proc.S b/arch/arm64/mm/proc.S
>> index 73886a5..3ea4f3b 100644
>> --- a/arch/arm64/mm/proc.S
>> +++ b/arch/arm64/mm/proc.S
>> @@ -55,17 +55,6 @@
>>
>>  #define MAIR(attr, mt) ((attr) << ((mt) * 8))
>>
>> -/*
>> - *     cpu_do_idle()
>> - *
>> - *     Idle the processor (wait for interrupt).
>> - */
>> -ENTRY(cpu_do_idle)
>> -       dsb     sy                              // WFI may enter a low-power mode
>> -       wfi
>> -       ret
>> -ENDPROC(cpu_do_idle)
>> -
>>  #ifdef CONFIG_CPU_PM
>>  /**
>>   * cpu_do_suspend - save CPU registers context
>> --
>> 1.9.1
>>
>>
>> _______________________________________________
>> linux-arm-kernel mailing list
>> linux-arm-kernel@...ts.infradead.org
>> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

-- 
Julien Thierry

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