linux-kernel - Re: [PATCH] arc: Mask individual IRQ lines during core INTC init

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Date:   Thu, 24 Aug 2017 15:11:02 -0700
From:   Vineet Gupta <Vineet.Gupta1@...opsys.com>
To:     Alexandru Gagniuc <alex.g@...ptrum.com>,
        Alexey Brodkin <Alexey.Brodkin@...opsys.com>,
        <linux-snps-arc@...ts.infradead.org>
CC:     <linux-kernel@...r.kernel.org>,
        Eugeniy Paltsev <Eugeniy.Paltsev@...opsys.com>
Subject: Re: [PATCH] arc: Mask individual IRQ lines during core INTC init

On 08/10/2017 12:10 PM, Alexandru Gagniuc wrote:
> On 08/10/2017 08:07 AM, Alexey Brodkin wrote:
>> ARC cores on reset have all interrupt lines of built-in INTC enabled.
>> Which means once we globally enable interrupts (very early on boot)
>> faulty hardware blocks may trigger an interrupt that Linux kernel
>> cannot handle yet as corresponding handler is not yet installed.
>>
>> In that case system falls in "interrupt storm" and basically never
>> does anything useful except entering and exiting generic IRQ handling
>> code.
>>
>> One real example of that kind of problematic hardware is DW GMAC which
>> also has interrupts enabled on reset and if Ethernet PHY informs GMAC
>> about link state, GMAC immediately reports that upstream to ARC core
>> and here we are.
>>
>> Now with that change we mask all individual IRQ lines making entire
>> system more fool-proof.

FWIW, hsdk doesn't boot to prompt with this patch !

I was queuing up hsdk support and ran into this !

-Vineet

>>
>> Signed-off-by: Alexey Brodkin <abrodkin@...opsys.com>
>> Cc: Eugeniy Paltsev <paltsev@...opsys.com>
>> Cc: Alexandru Gagniuc <alex.g@...ptrum.com>
> 
> Tested-by: Alexandru Gagniuc <alex.g@...ptrum.com>
> 
>> ---
>>  arch/arc/kernel/intc-arcv2.c   |  3 +++
>>  arch/arc/kernel/intc-compact.c | 14 +++++++++++++-
>>  2 files changed, 16 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/arc/kernel/intc-arcv2.c b/arch/arc/kernel/intc-arcv2.c
>> index f928795fd07a..cf90714a676d 100644
>> --- a/arch/arc/kernel/intc-arcv2.c
>> +++ b/arch/arc/kernel/intc-arcv2.c
>> @@ -75,10 +75,13 @@ void arc_init_IRQ(void)
>>       * Set a default priority for all available interrupts to prevent
>>       * switching of register banks if Fast IRQ and multiple register banks
>>       * are supported by CPU.
>> +     * Also disable all IRQ lines so faulty external hardware won't
>> +     * trigger interrupt that kernel is not ready to handle.
>>       */
>>      for (i = NR_EXCEPTIONS; i < irq_bcr.irqs + NR_EXCEPTIONS; i++) {
>>          write_aux_reg(AUX_IRQ_SELECT, i);
>>          write_aux_reg(AUX_IRQ_PRIORITY, ARCV2_IRQ_DEF_PRIO);
>> +        write_aux_reg(AUX_IRQ_ENABLE, 0);
>>      }
>>
>>      /* setup status32, don't enable intr yet as kernel doesn't want */
>> diff --git a/arch/arc/kernel/intc-compact.c b/arch/arc/kernel/intc-compact.c
>> index 7e608c6b0a01..cef388025adf 100644
>> --- a/arch/arc/kernel/intc-compact.c
>> +++ b/arch/arc/kernel/intc-compact.c
>> @@ -27,7 +27,7 @@
>>   */
>>  void arc_init_IRQ(void)
>>  {
>> -    int level_mask = 0;
>> +    int level_mask = 0, i;
>>
>>         /* Is timer high priority Interrupt (Level2 in ARCompact jargon) */
>>      level_mask |= IS_ENABLED(CONFIG_ARC_COMPACT_IRQ_LEVELS) << TIMER0_IRQ;
>> @@ -40,6 +40,18 @@ void arc_init_IRQ(void)
>>
>>      if (level_mask)
>>          pr_info("Level-2 interrupts bitset %x\n", level_mask);
>> +
>> +    /*
>> +     * Disable all IRQ lines so faulty external hardware won't
>> +     * trigger interrupt that kernel is not ready to handle.
>> +     */
>> +    for (i = TIMER0_IRQ; i < NR_CPU_IRQS; i++) {
>> +        unsigned int ienb;
>> +
>> +        ienb = read_aux_reg(AUX_IENABLE);
>> +        ienb &= ~(1 << i);
>> +        write_aux_reg(AUX_IENABLE, ienb);
>> +    }
>>  }
>>
>>  /*
>>
>