linux-kernel - Re: [PATCH v2] gpiolib: allow poll(2) on gpio value

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Message-ID: <359ed6810907021437m4417d4bfhc3d49b19387dbf96@mail.gmail.com>
Date:	Fri, 3 Jul 2009 00:37:26 +0300
From:	Jani Nikula <ext-jani.1.nikula@...ia.com>
To:	David Brownell <david-b@...bell.net>
Cc:	Daniel Glöckner <dg@...ix.com>,
	Ben Nizette <bn@...sdigital.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] gpiolib: allow poll(2) on gpio value

On Thu, Jul 2, 2009 at 21:57, David Brownell<david-b@...bell.net> wrote:
> On Thursday 02 July 2009, Jani Nikula wrote:
>> > Looks pretty clean.  Comments from anyone else?
>>
>> I'd appreciate a kernel side interface to gpio_setup_irq functionality
>> as well; now gpio_export from kernel won't setup support for poll(2)
>> nor is there any possibility to do so.
>
> I don't understand what you mean by this... there's no
> file descriptor open at that time, so there's no poll()
> that could be done.

I'm trying to say that if you call gpio_export() to create a sysfs
node, a subsequent poll() in user space won't work because there is no
irq set up, and sysfs_notify_dirent() won't be called. The patch
doesn't provide an interface for setting that up from kernel after
gpio_export() call - it's only possible to set up edge triggering and
sysfs notify by writing to the "edge" node from user space. That may
well be deemed sufficient, at least for now, and can be fixed later if
need be.

BR,
Jani.
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