linux-kernel - Re: [PATCH v4 3/3] gpio: add support for the Diolan DLN-2 USB GPIO driver

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Message-ID: <20140918124611.GA26817@localhost>
Date:	Thu, 18 Sep 2014 14:46:11 +0200
From:	Johan Hovold <johan@...nel.org>
To:	Octavian Purdila <octavian.purdila@...el.com>
Cc:	Johan Hovold <johan@...nel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Linus Walleij <linus.walleij@...aro.org>,
	Alexandre Courbot <gnurou@...il.com>, wsa@...-dreams.de,
	Samuel Ortiz <sameo@...ux.intel.com>,
	Lee Jones <lee.jones@...aro.org>,
	Arnd Bergmann <arnd@...db.de>,
	Daniel Baluta <daniel.baluta@...el.com>,
	Laurentiu Palcu <laurentiu.palcu@...el.com>,
	linux-usb@...r.kernel.org, lkml <linux-kernel@...r.kernel.org>,
	linux-gpio@...r.kernel.org, linux-i2c@...r.kernel.org
Subject: Re: [PATCH v4 3/3] gpio: add support for the Diolan DLN-2 USB GPIO
 driver

On Thu, Sep 18, 2014 at 03:43:07PM +0300, Octavian Purdila wrote:
> On Thu, Sep 18, 2014 at 1:54 PM, Johan Hovold <johan@...nel.org> wrote:
> > On Tue, Sep 09, 2014 at 10:24:46PM +0300, Octavian Purdila wrote:

> > Either way, it looks like this could race with get_direction() if you
> > get a set_direction() while get_direction() is retrieving the direction
> > from the device.
> >
> > This would break gpio_get().
> >
> I don't think gpio_set_direction() and gpio_get() are allowed to race.

I wrote that set_direction() and get_direction() could race, which in
turn would break gpio_get() as you would be caching the wrong
direction setting.

But perhaps gpiolib prevents this from happening.

Johan
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