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

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Date:   Thu, 8 Jun 2017 09:12:39 +0200
From:   Boris Brezillon <boris.brezillon@...e-electrons.com>
To:     Masahiro Yamada <yamada.masahiro@...ionext.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

Le Thu, 8 Jun 2017 15:10:18 +0900,
Masahiro Yamada <yamada.masahiro@...ionext.com> a écrit :

> 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;
>         }
> 
> 

My bad, I didn't notice you were releasing the lock after calling
reinit_completion(). I still find this solution more complex than my
proposal, but I don't care that much.

> 
> 
> 
> > 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;

Well, it was just a precaution, in case some interrupts weren't cleared
during the previous test (for example if they were masked before the
event actually happened, which can occur if you have a timeout, but
the event is detected afterward).

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

Anyway, you seem confident that you're doing the right thing, so I'll
let you decide what is appropriate and redirect any bug report to you if
that happens :-P.