linux-kernel - Re: [PATCH v2 4/5] ARC: MCIP: Set an initial affinity value in idu_irq

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Date:   Wed, 26 Oct 2016 15:05:31 +0100
From:   Marc Zyngier <marc.zyngier@....com>
To:     Vineet Gupta <Vineet.Gupta1@...opsys.com>,
        Yuriy Kolerov <yuriy.kolerov@...opsys.com>,
        linux-snps-arc@...ts.infradead.org
Cc:     Alexey.Brodkin@...opsys.com, tglx@...utronix.de,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 4/5] ARC: MCIP: Set an initial affinity value in
 idu_irq_map

On 25/10/16 19:28, Vineet Gupta wrote:
> On 10/24/2016 05:46 AM, Yuriy Kolerov wrote:
>> Originally an initial distribution mode (its value resides in Device Tree)
>> for each common interrupt is set in idu_irq_xlate. This leads to the
>> following problems. idu_irq_xlate may be called several times during parsing
>> of the Device Tree and it is semantically wrong to configure an initial
>> distribution mode here. Also a value of affinity (CPUs bitmap) is not saved
>> to irq_desc structure for the virq - later (after parsing of the DT) kernel
>> sees that affinity is not set and sets a default value of affinity (all
>> cores in round robin mode). As a result a value of affinity from Device
>> Tree is ignored.
>>
>> To fix it I created a buffer for initial CPUs bitmaps from Device Tree.
>> In idu_irq_xlate those bitmaps are saved to the buffer. Then affinity
>> for virq is set manually in idu_irq_map. It works because idu_irq_xlate
>> is always called before idu_irq_map.
>>
>> Despite the fact that it works I think that it must be rewritten to
>> eliminate usage of the buffer and move all logic to idu_irq_map but
>> I do not know how to do it correctly.
>>
>> Signed-off-by: Yuriy Kolerov <yuriy.kolerov@...opsys.com>
>> ---
>>  arch/arc/kernel/mcip.c | 15 +++++++++++----
>>  1 file changed, 11 insertions(+), 4 deletions(-)
>>
>> diff --git a/arch/arc/kernel/mcip.c b/arch/arc/kernel/mcip.c
>> index 51a218c..090f0a1 100644
>> --- a/arch/arc/kernel/mcip.c
>> +++ b/arch/arc/kernel/mcip.c
>> @@ -12,12 +12,15 @@
>>  #include <linux/irq.h>
>>  #include <linux/spinlock.h>
>>  #include <linux/irqdomain.h>
>> +#include <linux/interrupt.h>
>> +#include <linux/cpumask.h>
>>  #include <asm/irqflags-arcv2.h>
>>  #include <asm/mcip.h>
>>  #include <asm/setup.h>
>>  
>>  static char smp_cpuinfo_buf[128];
>>  static int idu_detected;
>> +static unsigned long idu_cirq_to_dest[CONFIG_ARC_NUMBER_OF_INTERRUPTS];
>>  
>>  static DEFINE_RAW_SPINLOCK(mcip_lock);
>>  
>> @@ -232,9 +235,15 @@ static void idu_cascade_isr(struct irq_desc *desc)
>>  
>>  static int idu_irq_map(struct irq_domain *d, unsigned int virq, irq_hw_number_t hwirq)
>>  {
>> +	cpumask_t mask;
>> +
>>  	irq_set_chip_and_handler(virq, &idu_irq_chip, handle_level_irq);
>>  	irq_set_status_flags(virq, IRQ_MOVE_PCNTXT);
>>  
>> +	cpumask_clear(&mask);
>> +	cpumask_bits(&mask)[0] |= idu_cirq_to_dest[hwirq];
>> +	irq_set_affinity(virq, &mask);
>> +
>>  	return 0;
>>  }
>>  
>> @@ -252,8 +261,7 @@ static int idu_irq_xlate(struct irq_domain *d, struct device_node *n,
>>  	if (distri == 0) {
>>  		/* 0 - Round Robin to all cpus, otherwise 1 bit per core */
>>  		raw_spin_lock_irqsave(&mcip_lock, flags);
>> -		idu_set_dest(hwirq, BIT(num_online_cpus()) - 1);
>> -		idu_set_mode(hwirq, IDU_M_TRIG_LEVEL, IDU_M_DISTRI_RR);
>> +		idu_cirq_to_dest[hwirq] = BIT(num_online_cpus()) - 1;
>>  		raw_spin_unlock_irqrestore(&mcip_lock, flags);
>>  	} else {
>>  		/*
>> @@ -267,8 +275,7 @@ static int idu_irq_xlate(struct irq_domain *d, struct device_node *n,
>>  				hwirq, cpu);
>>  
>>  		raw_spin_lock_irqsave(&mcip_lock, flags);
>> -		idu_set_dest(hwirq, cpu);
>> -		idu_set_mode(hwirq, IDU_M_TRIG_LEVEL, IDU_M_DISTRI_DEST);
>> +		idu_cirq_to_dest[hwirq] = cpu;
>>  		raw_spin_unlock_irqrestore(&mcip_lock, flags);
>>  	}
>>
> 
> So I missed this part - you are not touching the hardware here at all - and so we
> don't really need the spin lock check. Nevertheless, as you said off list, this
> patch is more of a hack and we really need to find a saner way of doing this !
> 
> @Marc, @tglx any guidance here - changelog at the top has the motivation for this
> hack !

It definitely feels weird to encode the interrupt affinity in the DT
(the kernel and possible userspace usually know much better than the
firmware). What is the actual reason for storing the affinity there?

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...