linux-kernel - Re: [PATCH v5 10/23] mtd: nand: denali: rework interrupt handling

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Date:   Thu, 8 Jun 2017 15:10:18 +0900
From:   Masahiro Yamada <yamada.masahiro@...ionext.com>
To:     Boris Brezillon <boris.brezillon@...e-electrons.com>
Cc:     Cyrille Pitchen <cyrille.pitchen@...ev4u.fr>,
        Richard Weinberger <richard@....at>,
        Marek Vasut <marek.vasut@...il.com>,
        David Woodhouse <dwmw2@...radead.org>,
        Chuanxiao Dong <chuanxiao.dong@...el.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Dinh Nguyen <dinguyen@...nel.org>,
        linux-mtd@...ts.infradead.org,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Artem Bityutskiy <artem.bityutskiy@...ux.intel.com>,
        Jassi Brar <jaswinder.singh@...aro.org>,
        Brian Norris <computersforpeace@...il.com>,
        Enrico Jorns <ejo@...gutronix.de>
Subject: Re: [PATCH v5 10/23] mtd: nand: denali: rework interrupt handling

Hi Boris,


2017-06-07 22:57 GMT+09:00 Boris Brezillon <boris.brezillon@...e-electrons.com>:
> On Wed,  7 Jun 2017 20:52:19 +0900
> Masahiro Yamada <yamada.masahiro@...ionext.com> wrote:
>
>
>> -/*
>> - * This is the interrupt service routine. It handles all interrupts
>> - * sent to this device. Note that on CE4100, this is a shared interrupt.
>> - */
>> -static irqreturn_t denali_isr(int irq, void *dev_id)
>> +static uint32_t denali_wait_for_irq(struct denali_nand_info *denali,
>> +                                 uint32_t irq_mask)
>>  {
>> -     struct denali_nand_info *denali = dev_id;
>> +     unsigned long time_left, flags;
>>       uint32_t irq_status;
>> -     irqreturn_t result = IRQ_NONE;
>>
>> -     spin_lock(&denali->irq_lock);
>> +     spin_lock_irqsave(&denali->irq_lock, flags);
>>
>> -     /* check to see if a valid NAND chip has been selected. */
>> -     if (is_flash_bank_valid(denali->flash_bank)) {
>> -             /*
>> -              * check to see if controller generated the interrupt,
>> -              * since this is a shared interrupt
>> -              */
>> -             irq_status = denali_irq_detected(denali);
>> -             if (irq_status != 0) {
>> -                     /* handle interrupt */
>> -                     /* first acknowledge it */
>> -                     clear_interrupt(denali, irq_status);
>> -                     /*
>> -                      * store the status in the device context for someone
>> -                      * to read
>> -                      */
>> -                     denali->irq_status |= irq_status;
>> -                     /* notify anyone who cares that it happened */
>> -                     complete(&denali->complete);
>> -                     /* tell the OS that we've handled this */
>> -                     result = IRQ_HANDLED;
>> -             }
>> +     irq_status = denali->irq_status;
>> +
>> +     if (irq_mask & irq_status) {
>> +             spin_unlock_irqrestore(&denali->irq_lock, flags);
>> +             return irq_status;
>>       }
>> -     spin_unlock(&denali->irq_lock);
>> -     return result;
>> +
>> +     denali->irq_mask = irq_mask;
>> +     reinit_completion(&denali->complete);
>
> These 2 instructions should be done before calling
> denali_wait_for_irq() (for example in denali_reset_irq()), otherwise
> you might loose events if they happen between your irq_status read and
> the reinit_completion() call.

No.

denali->irq_lock avoids a race between denali_isr() and
denali_wait_for_irq().


The line
     denali->irq_status |= irq_status;
in denali_isr() accumulates all events that have happened
since denali_reset_irq().

If the interested IRQs have already happened
before denali_wait_for_irq(), it just return immediately
without using completion.

I do not mind adding a comment like below
if you think my intention is unclear, though.

        /* Return immediately if interested IRQs have already happend. */
        if (irq_mask & irq_status) {
                spin_unlock_irqrestore(&denali->irq_lock, flags);
                return irq_status;
        }





> You should also clear existing interrupts
> before launching your operation, otherwise you might wakeup on previous
> events.


I do not see a point in your suggestion.

denali_isr() reads out IRQ_STATUS(i) and immediately clears IRQ bits.

IRQ events triggered by previous events are accumulated in denali->irq_status.

denali_reset_irq() clears it.

        denali->irq_status = 0;


Again, denali->irq_lock avoids a race between denali_reset_irq() and
denali_irq(),
so this works correctly.


-- 
Best Regards
Masahiro Yamada