linux-kernel - Re: [PATCH 08/22] gpiolib: cdev: complete the irq/thread timestamp handshake

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Message-ID: <20200625100126.GA18788@sol>
Date:   Thu, 25 Jun 2020 18:01:26 +0800
From:   Kent Gibson <warthog618@...il.com>
To:     Bartosz Golaszewski <bgolaszewski@...libre.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        linux-gpio <linux-gpio@...r.kernel.org>,
        Linus Walleij <linus.walleij@...aro.org>
Subject: Re: [PATCH 08/22] gpiolib: cdev: complete the irq/thread timestamp
 handshake

On Thu, Jun 25, 2020 at 11:44:30AM +0200, Bartosz Golaszewski wrote:
> On Wed, Jun 24, 2020 at 4:08 PM Kent Gibson <warthog618@...il.com> wrote:
> >
> > On Wed, Jun 24, 2020 at 04:00:42PM +0200, Bartosz Golaszewski wrote:
> > > wt., 23 cze 2020 o 06:02 Kent Gibson <warthog618@...il.com> napisał(a):
[ snip ]
> >
> > I'm not totally sure myself, as my understanding of how interrupts are
> > shared in the kernel is pretty sketchy, but my concern is that if we
> > are sharing the irq then whoever we are sharing with may release the irq
> > and we go from nested to unnested.  Or vice versa.  Not sure if that is
> > valid, but that was my concern, and it seemed like a minor change to
> > cover it just in case.
> >
> 
> It's my understanding that a shared interrupt must be explicitly
> requested as shared by all previous users or request_irq() will fail.
> In this case: we call request_threaded_irq() without the IRQF_SHARED
> flag so it's never a shared interrupt. Even if someone previously
> requested it as shared - our call will simply fail.
> 

OK.  Is there a reason not to share the interrupt?

> I still think that resetting the timestamp is fine because it's not
> being set to 0 in hardirq context. We just need a different
> explanation.
> 

Or just drop it?

Cheers,
Kent.