From: Johan Hovold <johan@kernel.org>
To: Octavian Purdila <octavian.purdila@intel.com>
Cc: Johan Hovold <johan@kernel.org>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Linus Walleij <linus.walleij@linaro.org>,
Alexandre Courbot <gnurou@gmail.com>,
wsa@the-dreams.de, Samuel Ortiz <sameo@linux.intel.com>,
Lee Jones <lee.jones@linaro.org>, Arnd Bergmann <arnd@arndb.de>,
Daniel Baluta <daniel.baluta@intel.com>,
Laurentiu Palcu <laurentiu.palcu@intel.com>,
linux-usb@vger.kernel.org, lkml <linux-kernel@vger.kernel.org>,
linux-gpio@vger.kernel.org, linux-i2c@vger.kernel.org
Subject: Re: [PATCH v4 3/3] gpio: add support for the Diolan DLN-2 USB GPIO driver
Date: Fri, 19 Sep 2014 09:11:39 +0200 [thread overview]
Message-ID: <20140919071139.GE26817@localhost> (raw)
In-Reply-To: <CAE1zotK7nb6VVp5a3n2_fnWZQHfizg4hFFy-ZVW5fzyFwmBMcA@mail.gmail.com>
On Thu, Sep 18, 2014 at 06:54:34PM +0300, Octavian Purdila wrote:
> On Thu, Sep 18, 2014 at 3:46 PM, Johan Hovold <johan@kernel.org> wrote:
> > 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@kernel.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.
> >
>
> OK, I now see the problem. I think doing this in get_direction() will
> fix the issue:
>
> if (!test_and_set_bit(offset, dln2->pin_dir_set))
> set/clear_bit(offset, dln2->pin_dir);
>
> because gpiolib calls get_direction() while requesting a pin and
> request cannot race with itself. Which means that get_direction() can
> not race with itself the first time it is called, when the set/clear
> operation will be run.
>
> And because we know that get_direction() is called first, we can even
> remove the set/clear operation from set_direction().
Why not simply fetch the direction in request() and get rid of the
pin_dir_set bitmask?
Johan
prev parent reply other threads:[~2014-09-19 7:14 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-09-09 19:24 [PATCH v4 0/3] mfd: add support for Diolan DLN-2 Octavian Purdila
2014-09-09 19:24 ` [PATCH v4 1/3] mfd: add support for Diolan DLN-2 devices Octavian Purdila
2014-09-16 23:21 ` Lee Jones
2014-09-17 7:25 ` Octavian Purdila
2014-09-17 7:38 ` Johan Hovold
2014-09-17 15:56 ` Lee Jones
2014-09-17 9:10 ` Johan Hovold
2014-09-17 15:46 ` Lee Jones
2014-09-18 11:31 ` Johan Hovold
2014-09-18 14:21 ` Johan Hovold
2014-09-09 19:24 ` [PATCH v4 2/3] i2c: add support for Diolan DLN-2 USB-I2C adapter Octavian Purdila
2014-09-17 9:44 ` Johan Hovold
2014-09-17 10:07 ` Octavian Purdila
2014-09-18 8:19 ` Johan Hovold
2014-09-18 8:49 ` Octavian Purdila
2014-09-18 9:13 ` Johan Hovold
2014-09-09 19:24 ` [PATCH v4 3/3] gpio: add support for the Diolan DLN-2 USB GPIO driver Octavian Purdila
2014-09-18 10:54 ` Johan Hovold
2014-09-18 12:43 ` Octavian Purdila
2014-09-18 12:46 ` Johan Hovold
2014-09-18 15:54 ` Octavian Purdila
2014-09-19 7:11 ` Johan Hovold [this message]
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