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Subject: Re: [PATCH V2] irqchip/loongson-pch-pic: Update interrupt
 registration policy
To: Christophe JAILLET <christophe.jaillet@wanadoo.fr>,
 chenhuacai@kernel.org, jiaxun.yang@flygoat.com, tglx@linutronix.de
Cc: linux-mips@vger.kernel.org, linux-kernel@vger.kernel.org,
 Baoqi Zhang <zhangbaoqi@loongson.cn>, Biao Dong <dongbiao@loongson.cn>
References: <20240316082141.26139-1-zhangtianyang@loongson.cn>
 <0fda46c7-87e1-41f1-b3f0-ee3d1a4ac601@wanadoo.fr>
From: Tianyang Zhang <zhangtianyang@loongson.cn>
Message-ID: <45b36854-fd80-a410-6cca-f3b776566de6@loongson.cn>
Date: Tue, 19 Mar 2024 19:26:26 +0800
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Hi Christophe

This part of the code is not a hotspot path. In fact, it may only be 
executed once at startup,

so some optimizations that we consider extreme can be omitted

Tianyang

在 2024/3/16 下午10:03, Christophe JAILLET 写道:
> Le 16/03/2024 à 09:21, Tianyang Zhang a écrit :
>> From: Baoqi Zhang <zhangbaoqi@loongson.cn>
>>
>> This patch remove the fixed mapping between the 7A interrupt source
>> and the HT interrupt vector, and replaced it with a dynamically
>> allocated approach.
>>
>> We introduce a mapping table in struct pch_pic, where each interrupt
>> source will allocate an index as a 'hwirq' from the table in the order
>> of application and set table value as interrupt source number. This 
>> hwirq
>> will be configured as its vector in the HT interrupt controller. For an
>> interrupt source, the validity period of the obtained hwirq will last 
>> until
>> the system reset
>>
>> This will be more conducive to fully utilizing existing vectors to
>> support more devices
>>
>> Signed-off-by: Baoqi Zhang <zhangbaoqi@loongson.cn>
>> Signed-off-by: Biao Dong <dongbiao@loongson.cn>
>> Signed-off-by: Tianyang Zhang <zhangtianyang@loongson.cn>
>> ---
>>   drivers/irqchip/irq-loongson-pch-pic.c | 77 ++++++++++++++++++++------
>>   1 file changed, 59 insertions(+), 18 deletions(-)
>>
>
> ...
>
>> @@ -171,6 +183,27 @@ static int pch_pic_domain_translate(struct 
>> irq_domain *d,
>>               return -EINVAL;
>>             *hwirq = fwspec->param[0] - priv->gsi_base;
>> +
>> +        raw_spin_lock_irqsave(&priv->pic_lock, flags);
>> +        /* Check pic-table to confirm if the hwirq has been assigned */
>> +        for (i = 0; i < priv->inuse; i++) {
>> +            if (priv->table[i] == *hwirq) {
>> +                *hwirq = i;
>> +                break;
>> +            }
>> +        }
>> +        if (i == priv->inuse) {
>> +            /* Assign a new hwirq in pic-table */
>> +            if (priv->inuse >= PIC_COUNT) {
>> +                pr_err("pch-pic domain has no free vectors\n");
>> + raw_spin_unlock_irqrestore(&priv->pic_lock, flags);
>> +                return -EINVAL;
>> +            }
>> +            priv->table[priv->inuse] = *hwirq;
>> +            *hwirq = priv->inuse++;
>> +        }
>> +        raw_spin_unlock_irqrestore(&priv->pic_lock, flags);
>
> Hi,
>
> not sure if it helps or if this is a hot path, but, IIUC, taking the 
> lock could be avoided with some code reordering and 'inuse' being an 
> atomic_t.
>
> IIUC, the lock is only needed to protect 'inuse' and 'table' is never 
> modified afterwards.
>
> Somehing like:
>
> > +        int cur_inuse;
>         ...
> > +        cur_inuse = atomic_read(&priv->inuse);
> > +        /* Check pic-table to confirm if the hwirq has been 
> assigned */
> > +        for (i = 0; i < cur_inuse; i++) {
> > +            if (priv->table[i] == *hwirq) {
> > +                *hwirq = i;
> > +                break;
> > +            }
> > +        }
> > +        if (i == cur_inuse) {
> > +            /* Assign a new hwirq in pic-table */
> > +            if (cur_inuse >= PIC_COUNT) {
> > +                pr_err("pch-pic domain has no free vectors\n");
> > +                return -EINVAL;
> > +            }
> > +            priv->table[cur_inuse] = *hwirq;
> > +            *hwirq = atomic_inc_return(&priv->inuse);
> > +        }
>
>
>> +
>>           if (fwspec->param_count > 1)
>>               *type = fwspec->param[1] & IRQ_TYPE_SENSE_MASK;
>>           else
>> @@ -194,6 +227,9 @@ static int pch_pic_alloc(struct irq_domain 
>> *domain, unsigned int virq,
>>       if (err)
>>           return err;
>>   +    /* Write vector ID */
>> +    writeb(priv->ht_vec_base + hwirq, priv->base + 
>> PCH_INT_HTVEC(hwirq_to_bit(priv, hwirq)));
>> +
>>       parent_fwspec.fwnode = domain->parent->fwnode;
>>       parent_fwspec.param_count = 1;
>>       parent_fwspec.param[0] = hwirq + priv->ht_vec_base;
>
> ...