linux-kernel - Re: [PATCH v1] gpio: dwapb: mask/unmask IRQ when disable/enable it

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Date:   Sun, 6 Dec 2020 01:15:22 +0300
From:   Serge Semin <fancer.lancer@...il.com>
To:     luojiaxing <luojiaxing@...wei.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jason Cooper <jason@...edaemon.net>,
        Marc Zyngier <maz@...nel.org>
Cc:     Andy Shevchenko <andy.shevchenko@...il.com>,
        bgolaszewski@...libre.com, linus.walleij@...aro.org,
        linux-gpio@...r.kernel.org, linux-kernel@...r.kernel.org,
        linuxarm@...wei.com
Subject: Re: [PATCH v1] gpio: dwapb: mask/unmask IRQ when disable/enable it

On Tue, Dec 01, 2020 at 04:59:21PM +0800, luojiaxing wrote:
> 
> On 2020/11/30 19:22, Andy Shevchenko wrote:
> > On Mon, Nov 30, 2020 at 05:36:19PM +0800, Luo Jiaxing wrote:
> > > The mask and unmask registers are not configured in dwapb_irq_enable() and
> > > dwapb_irq_disable(). In the following situations, the IRQ will be masked by
> > > default after the IRQ is enabled:
> > > 
> > > mask IRQ -> disable IRQ -> enable IRQ
> > > 
> > > In this case, the IRQ status of GPIO controller is inconsistent with it's
> > > irq_data too. For example, in __irq_enable(), IRQD_IRQ_DISABLED and
> > > IRQD_IRQ_MASKED are both clear, but GPIO controller do not perform unmask.
> > Sounds a bit like a papering over the issue which is slightly different.
> > Can you elaborate more, why ->irq_mask() / ->irq_unmask() are not being called?
> 
> 
> Sure, The basic software invoking process is as follows:
> 
> Release IRQ:
> free_irq() -> __free_irq() -> irq_shutdown() ->__irq_disable()
> 
> Disable IRQ:
> disable_irq() -> __disable_irq_nosync() -> __disable_irq -> irq_disable ->
> __irq_disable()
> 
> As shown before, both will call __irq_disable(). The code of it is as
> follows:
> 
> if (irqd_irq_disabled(&desc->irq_data)) {
>     if (mask)
>         mask_irq(desc);
> 
> } else {
>         irq_state_set_disabled(desc);
>             if (desc->irq_data.chip->irq_disable) {
> desc->irq_data.chip->irq_disable(&desc->irq_data);
>                 irq_state_set_masked(desc);
>             } else if (mask) {
>                 mask_irq(desc);
>     }
> }
> 
> Because gpio-dwapb.c provides the hook function of irq_disable,
> __irq_disable() will directly calls chip->irq_disable() instead of
> mask_irq().
> 
> For irq_enable(), it's similar and the code is as follows:
> 
> if (!irqd_irq_disabled(&desc->irq_data)) {
>     unmask_irq(desc);
> } else {
>     irq_state_clr_disabled(desc);
>     if (desc->irq_data.chip->irq_enable) {
> desc->irq_data.chip->irq_enable(&desc->irq_data);
>         irq_state_clr_masked(desc);
>     } else {
>         unmask_irq(desc);
>     }
> }
> 
> Similarly, because gpio-dwapb.c provides the hook function of irq_enable,
> irq_enable() will directly calls chip->irq_enable() but does not call
> unmask_irq().
> 
> 
> Therefore, the current handle is as follows:
> 
> API of IRQ:        |   mask_irq()             | disable_irq()           
> |    enable_irq()
> 
> gpio-dwapb.c:  |   chip->irq_mask()   | chip->irq_diable()   |   
> chip->irq_enable()
> 
> I do not know why irq_enable() only calls chip->irq_enable(). However, the
> code shows that irq_enable() clears the disable and masked flags in the
> irq_data state.
> 
> Therefore, for gpio-dwapb.c, I thinks ->irq_enable also needs to clear the
> disable and masked flags in the hardware register.
> 

Hmm, that sounds like a problem, but the explanation is a bit unclear
to me. AFAICS you are saying that the only callbacks which are
called during the IRQ request/release are the irq_enable(), right? If
so then the only reason why we haven't got a problem reported due to
that so far is that the IRQs actually unmasked by default.

In anyway I'd suggest to join someone from the kernel IRQs-related
subsystem to this discussion to ask their opinion whether the IRQs
setup procedure is supposed to work like you say and the irq_enable
shall actually also unmask IRQs.

Thomas, Jason, Mark, could you give us your comment about the issue?

-Sergey

> 
> 
>