linux-kernel - Re: [PATCH v2 0/6] gpio: cdev: bail out of poll() if the device goes down

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Message-ID: <ZN9ySmxxdoLODcc9@smile.fi.intel.com>
Date:   Fri, 18 Aug 2023 16:29:46 +0300
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Bartosz Golaszewski <brgl@...ev.pl>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        Kent Gibson <warthog618@...il.com>, linux-gpio@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
Subject: Re: [PATCH v2 0/6] gpio: cdev: bail out of poll() if the device goes
 down

On Fri, Aug 18, 2023 at 02:06:21PM +0200, Bartosz Golaszewski wrote:
> On Fri, Aug 18, 2023 at 12:34 PM Andy Shevchenko
> <andriy.shevchenko@...ux.intel.com> wrote:
> >
> > On Thu, Aug 17, 2023 at 08:49:52PM +0200, Bartosz Golaszewski wrote:
> > > From: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
> > >
> > > Wake up all three wake queues (the one associated with the character
> > > device file, the one for V1 line events and the V2 line request one)
> > > when the underlying GPIO device is unregistered. This way we won't get
> > > stuck in poll() after the chip is gone as user-space will be forced to
> > > go back into a new system call and will see that gdev->chip is NULL.
> >
> > Why can't you use the global device unbind notifications and filter out
> > what you are interested in?
> 
> There's no truly global device unbind notification - only per-bus.
> GPIO devices can reside on any bus, there are no limitations and so
> we'd have to subscribe to all of them.

We have, but it requires a bit of code patching.
Look at device_platform_notify()/device_platform_notify_remove().

I noticed, btw, that platform_notify() and Co is a dead code :-)
Maybe it can be converted to a list and a manager of that list,
so specific cases can utilize it.

-- 
With Best Regards,
Andy Shevchenko